JP2009016384A - Control method of illumination device, and driving method of liquid crystal display device assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method of an illumination device capable of compensating for irreversible temporal variation in forward voltage value V<SB>f</SB>of a light emitting element. <P>SOLUTION: In the control method of the illumination device including the light emitting element 22, a light emitting element driving control circuit 90 which supplies a current to the light emitting element 22 and measures a forward voltage value of the light emitting element 22, and a temperature measuring means 70 of measuring ambient temperature in a circumference of the light emitting element 22, the light emitting element driving control circuit 90 measures an initial forward voltage value V<SB>f-0</SB>and the temperature measuring means 70 measures initial ambient temperature T<SB>0</SB>when the illumination device is started up, and the light emitting element driving control circuit 90 measures a forward voltage value V<SB>f-0</SB>when the illumination device is in operation, thereby determining driving conditions of the light emitting element 22 based upon the initial forward voltage value V<SB>f-0</SB>, forward voltage value V<SB>f</SB>, and initial ambient temperature T<SB>0</SB>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for controlling an illumination device and a method for driving a liquid crystal display device assembly.

  In the liquid crystal display device, the liquid crystal material itself does not emit light. Therefore, for example, a direct type planar light source device (backlight) that illuminates the display area of the liquid crystal display device is disposed on the back surface of the display area. In the color liquid crystal display device, one pixel is composed of, for example, three subpixels of a red light emitting subpixel, a green light emitting subpixel, and a blue light emitting subpixel. Then, the liquid crystal cell constituting each pixel or each sub-pixel is operated as a kind of light shutter (light valve), that is, by controlling the light transmittance of each pixel or each sub-pixel. An image is displayed by controlling the light transmittance of illumination light (for example, white light) emitted from the light source device.

  Conventionally, a planar light source device in a liquid crystal display device assembly illuminates the entire display area with uniform and constant brightness. However, the planar light source device has a configuration different from such a planar light source device, that is, a plurality of planar light source devices. For example, Japanese Unexamined Patent Application Publication No. 2005-017324 discloses a planar light source device having a configuration in which the distribution of illuminance in a plurality of display area units constituting a liquid crystal display device is changed. The planar light source unit disclosed in JP 2005-017324 includes a red light emitting diode, a green light emitting diode, and a blue light emitting diode. Then, illumination light is emitted from white light with high color purity obtained by mixing red light emitted from the red light emitting diode, green light emitted from the green light emitting diode, and blue light emitted from the blue light emitting diode. It is said.

By the way, the light emitting diode generates heat during driving. Even when driving under the same conditions, the forward voltage characteristic ( _Vf characteristic) fluctuates as a result of heat generation, and the light output from the light emitting diode decreases, but the reduction rate is red. Different for light emitting diode, green light emitting diode, and blue light emitting diode. Therefore, white light as illumination light is obtained by mixing the light of each color emitted from the red light emitting diode, green light emitting diode, and blue light emitting diode. The chromaticity and white balance of this white light (color Variations in temperature).

  That is, in a light emitting diode used in a planar light source device, a current of about several hundred mA to 1 A is supplied and heat of about several watts is released. Therefore, the temperature of the light emitting diode rises considerably. For example, in a light emitting diode having a thermal resistance value of 10 ° C./W, when 2 watts of heat is released, the temperature of the light emitting diode is 20 ° C. higher than the ambient temperature (referred to as ambient temperature). . As described above, the temperature rise due to the heat generation of the light emitting diode itself and the fluctuation of the ambient temperature affect the light emitting characteristics of the light emitting diode.

  10A, 10B, and 11 show the ambient temperature dependence of the light emission intensity of the light emitting diode. Here, the blue light emitting diode and the green light emitting diode are made of InGaN light emitting diodes, and the red light emitting diode is made of an AlGaInP light emitting diode. Although any color has an ambient temperature dependency, the ambient temperature dependency of a red light emitting diode is particularly remarkable. FIG. 12 shows the ambient temperature dependency of the light emission amount and the dominant wavelength of the blue light emitting diode. As the ambient temperature increases, the light emission amount decreases linearly, and the dominant wavelength linearly changes to the longer wavelength side. . Such an ambient temperature dependency of the light emitting diode causes variations in color temperature and luminance, and uneven temperature in the planar light source device causes uneven color and uneven luminance in the liquid crystal display device.

  Therefore, in the technique disclosed in Japanese Patent Application Laid-Open No. 2005-017324, the amount of drive current detected by the drive current detection unit is fed back to the drive control unit, and the result of comparison between the amount of returned drive current and a predetermined amount of current. Based on the above, the white balance of the display image is controlled by changing the drive control signal to control the light emission amounts of the three color light emitting devices.

On the other hand, controlling the surface light source device based on the method described below is disclosed, for example, in JP-A-11-109317. That is, the maximum luminance of the light source constituting the planar light source device is set to Y _max, and the maximum value (specifically, for example, 100%) of the light transmittance (aperture ratio) of the pixel in the display area is set to Lt _max . Further, when the light source constituting the planar light source device has the maximum luminance Y _max , the light transmittance (aperture ratio) of each pixel for obtaining the display luminance y ₀ in the display area is Lt ₀ . Then, in this case, the light source luminance Y ₀ of the light source constituting the planar light source device is
Y ₀ · Lt _max = Y _max · Lt ₀
It may be controlled so as to satisfy In addition, the conceptual diagram of such control is shown to (A) and (B) of FIG. Here, the light source luminance Y ₀ is changed for each frame in the image display of the liquid crystal display device.

JP 2005-017324 A JP-A-11-109317 JP 2005-115350 A

By the way, as described above, the forward voltage characteristic ( _Vf characteristic) of the light emitting diode not only reversibly changes due to heat generation during driving, but also changes over time due to long-term energization and storage. In addition, an irreversible change in the light emission amount of the light emitting element is often observed.

The variation with time of the forward voltage value V _f of the light emitting diode aged with a constant current is shown. FIG. 15 shows the amount of light emission, and FIGS. Here, FIG. 14A shows the relationship between the lighting time and the forward voltage value V _f (relative value), and FIG. 14B shows the case where it is stored in an environment of 85 ° C. The relationship between the storage time and the forward voltage value V _f (relative value) is shown, and FIG. 15 shows the relationship between the storage time and the light emission amount (relative value) when stored in an environment of 85 ° C. . In either case, the forward voltage value V _f varies on the order of several percent over several thousand hours. Further, FIG. 16A shows a graph in which the relationship between the forward current value _If and the forward voltage value _Vf is measured, and FIG. 16B shows the junction temperature _Tj and the forward voltage value _Vf. The graph which measured the relationship with is shown. When determining the forward current value I _f to a certain value, V _f can be expressed by a linear function of T _j. From FIG. 16B, the temperature coefficient of the forward voltage value V _f with respect to the junction temperature T _j is about −0.1% / ° C. Therefore, if the forward voltage value V _f irreversibly fluctuates, for example, by 2% over a long period of aging, it is mistaken for a change in the junction temperature T _j as much as 20 ° C.

  In addition, the irreversible change in the light emission amount of the light emitting element is mainly caused by, for example, discoloration or coloring of the filler or cap resin used for assembling the light emitting element.

  A projector having a temperature measuring device provided with a junction temperature calculating means is known from JP-A-2005-115350. However, this Japanese Patent Application Laid-Open No. 2005-115350 does not mention anything about the forward voltage characteristics of the light emitting diodes fluctuating with time and dealing with the fluctuations with time.

Accordingly, a first object of the present invention is to provide a method for controlling an illuminating device and a method for driving a liquid crystal display device assembly that can compensate for irreversible temporal variation of the forward voltage value V _f of the light emitting element. is there. A second object of the present invention is to provide a method for controlling an illumination device and a method for driving a liquid crystal display device assembly that can compensate for an irreversible change in the light emission amount of a light emitting element.

The control method of the lighting device according to the first aspect of the present invention for achieving the first object is as follows.
(A) a light emitting element,
(B) a light emitting element drive control circuit for supplying a current to the light emitting element and measuring a forward voltage value of the light emitting element;
(C) a temperature measuring means for measuring the ambient temperature around the light emitting element;
A control method for a lighting device comprising:
At the start of the lighting device, the initial forward voltage value V _f-0 is measured by the light emitting element drive control circuit, and the initial ambient temperature T ₀ is measured by the temperature measuring means.
During the operation of the lighting device, the forward voltage value V _f is measured by the light emitting element drive control circuit, and based on the initial forward voltage value V _f-0 , the forward voltage value V _f and the initial ambient temperature T ₀ , The driving condition of the light emitting element is determined.

The method for controlling the lighting device according to the second aspect of the present invention to achieve the second object is as follows.
(A) a light emitting element, and
(B) a light emitting element drive control circuit for supplying a current to the light emitting element and measuring the light emission amount and the forward voltage value of the light emitting element;
A control method for a lighting device comprising:
When the lighting device is started up, the light emission element drive control circuit measures the initial light emission amount P ₀ and the initial forward voltage value V _f-0 ,
During operation of the lighting device, the forward voltage value V _f is measured by the light emitting element drive control circuit, and the light emitting element is based on the initial light emission amount P ₀ , the initial forward voltage value V _f-0 and the forward voltage value V _f. The driving condition is determined.

A method for driving a liquid crystal display device assembly according to the first aspect of the present invention for achieving the first object is as follows.
(A) a liquid crystal display device, and
(B) a planar light source device for illuminating the liquid crystal display device from the back surface;
A method of driving a liquid crystal display device assembly comprising:
The planar light source device
(A) a light emitting element,
(B) a light emitting element drive control circuit for supplying a current to the light emitting element and measuring a forward voltage value of the light emitting element;
(C) a temperature measuring means for measuring the ambient temperature around the light emitting element;
It has
At the time of starting the surface light source device, the initial forward voltage value V _f-0 is measured by the light emitting element drive control circuit, and the initial ambient temperature T ₀ is measured by the temperature measuring means.
During the operation of the planar light source device, the forward voltage value V _f is measured by the light emitting element drive control circuit, and the initial forward voltage value V _f-0 , the forward voltage value V _f and the initial ambient temperature T ₀ are set. Based on this, the driving condition of the light emitting element is determined.

The method for driving the liquid crystal display device assembly according to the second aspect of the present invention for achieving the second object is as follows.
(A) a liquid crystal display device, and
(B) a planar light source device for illuminating the liquid crystal display device from the back surface;
A method of driving a liquid crystal display device assembly comprising:
The planar light source device
(A) a light emitting element, and
(B) a light emitting element drive control circuit for supplying a current to the light emitting element and measuring the light emission amount and the forward voltage value of the light emitting element;
It has
When starting the planar light source device, the light emission element drive control circuit measures the initial light emission amount P ₀ and the initial forward voltage value V _f-0 ,
During operation of the planar light source device, the forward voltage value V _f is measured by the light emitting element drive control circuit, and based on the initial light emission amount P ₀ , the initial forward voltage value V _f-0 and the forward voltage value V _f , The driving condition of the light emitting element is determined.

The lighting device control method or the liquid crystal display device driving method according to the first aspect or the second aspect of the present invention (hereinafter, these may be collectively referred to simply as “the method of the present invention”). )
A timer,
The time from the end of operation of the lighting device (planar light source device) to the next start-up is measured with a timer, and if the measured time is less than a predetermined time, the next startup of the lighting device (planar light source device) In the raising, based on the initial forward voltage value V _f-0 and the initial atmospheric temperature T ₀ which were obtained during the operation of the previous lighting device (planar light source device), or alternatively, the previous lighting device (planar shape) The driving condition of the light emitting element can be determined based on the initial light emission amount P ₀ and the initial forward voltage value V _f-0 obtained during the operation of the light source device. By providing the timer in this way, the initial forward voltage value V _f can be obtained in a state where the left-handed time has not elapsed since the end of the operation of the illumination device (planar light source device) and the light-emitting element has not cooled sufficiently. _-0 or alternatively, the initial light emission amount P ₀ and the initial forward voltage value V _f-0 are measured, and the accurate initial forward voltage value V _f-0 , or the initial light emission amount P ₀ and the initial forward voltage value are measured. It is possible to reliably prevent the occurrence of a problem that the directional voltage value V _f-0 is not measured. The predetermined time may be determined by measuring the temperature change of the light emitting element from the end of the operation of the lighting device (planar light source device) to the ambient temperature.

In the method of the present invention including the above preferred embodiment, the initial forward voltage value V _f-0 and the forward voltage value V _f are controlled by the light emitting element drive control circuit during the operation of the illumination device (planar light source device). And a driving current for driving the light emitting element is determined based on the value of the initial ambient temperature T ₀ , or based on the initial light emission amount P ₀ , the initial forward voltage value V _f-0 and the forward voltage value V _f. In addition, the light emitting element can be driven with the determined driving current. In this case, in the light emitting element drive control circuit, a value of T ₀ − (V _f −V _f−0 ) / B (where B is a constant) is obtained, or P ₀ − (V _f −V _{f −0} ) × (D / B) (where B and D are constants), and the drive current can be determined based on the obtained values.

  Furthermore, in the control method of the illumination device of the present invention including the above-described preferred embodiment, it is preferable that the transmissive liquid crystal display device is illuminated from the back by the illumination device.

In general, when forming the light emitting element from a light emitting diode (LED), light emission characteristics of the light emitting diode is determined by the junction temperature T _j, the junction temperature T _j is very strong correlation between the forward voltage value V _f. Therefore, when the forward voltage value V _f is measured, the light emission characteristic can be known through the junction temperature T _j . The junction temperature T _j , the forward voltage value V _f, and the forward current value _If are related by the following formula. However, V _f >> 0. The junction temperature T _j is also referred to as a junction temperature and refers to the temperature of a semiconductor pn junction.

_{I f = a · exp [-} (E g -e · V f) / kT j] (A)
Therefore,
V _f = (E _g / e) − (k · T _j / e) × ln (a / I _f ) (B)
It becomes. However,
E _g : band gap energy (unit: eV)
e: unit charge (unit: C)
k: Boltzmann constant a: constant.

Therefore, when “B” is a constant, the following formula (C) can be obtained by modifying the formula (B).
V _f = A−B · T _j (C)
However,
A≡E _g / e
B≡ (k / e) × ln (a / I _f )
It is.

When the lighting device or the planar light source device is started up, the light emitting element is usually equal to the ambient temperature. In a state where such a light emitting element is not in a light emitting state, a reference pulse having a predetermined constant current value, that is, having a predetermined initial driving current value I ₀ is supplied to the light emitting element. Specifically, a predetermined initial drive current value I ₀ (for example, 200 mA) is allowed to flow through the light emitting element for a predetermined time (for example, 5 microseconds). Under such conditions, the junction temperature T _j of the light emitting element does not increase. Therefore, the ambient temperature (initial ambient temperature T ₀ ) at this time can be regarded as the junction temperature T _j .

In the lighting device control method or the liquid crystal display device driving method according to the first aspect of the present invention, the forward voltage value (initial forward voltage value V _f-0 ) at this time is measured. At the time of starting up such an illumination device (planar light source device), the initial forward voltage value V _f-0 is measured by the light emitting element drive control circuit, and the initial ambient temperature T ₀ is also measured by the temperature measuring means. The measurement operation is sometimes referred to as “reference measurement mode”. By this kind of calibration operation, the value of the coefficient “A” can be obtained from the equation (C). The forward voltage value V _f varies irreversibly due to the aging of the light emitting element, and this is due to the variation of the value of the coefficient “A” in the following equation (D). Therefore, by obtaining the value of the coefficient “A” in the equation (D) by the calibration operation, the light emitting element in the operation of the illumination device or the planar light source device (sometimes referred to as “normal light emission mode”). The light emission state can be compensated.

A = V _f-0 + B · T ₀ (D)

Further, at various atmospheric temperatures, an operation is performed such that various light emitting element driving currents flow for a predetermined time (for example, 5 microseconds) with respect to the light emitting elements having the same temperature as the atmospheric temperature. The relationship between _j , the forward voltage value _Vf, and the light emitting element driving current (see, for example, (A) and (B) in FIG. 16) is obtained in advance, and further, the value of the constant “B” is obtained.

On the other hand, the forward voltage value V _f is measured during operation of the illumination device or the planar light source device, that is, in the normal light emission mode. And from formula (C) and formula (D), junction temperature _Tj can be obtained based on the following formula (E).

T _j = T ₀ − (V _f −V _f−0 ) / B (E)

Based on the junction temperature T _j thus obtained or the values of the initial forward voltage value V _f-0 , the forward voltage value V _f and the initial ambient temperature T ₀ , the junction temperature previously obtained is further determined. Based on the relationship between T _j , the forward voltage value V _f, and the light emitting element driving current, the driving condition of the light emitting element, for example, the driving current for driving the light emitting element can be determined. And a light emitting element is light-emitted by driving a light emitting element based on this determined drive condition. In addition, the above operation is performed by the light emitting element drive control circuit as described above.

The light emission amount P (T _j ) can be expressed by a linear function of the junction temperature T _j of the light emitting element as shown in the following formula (F-1) (see FIG. 12). Further, assuming that the light emission amount obtained when a current is passed through the light emitting element based on the reference pulse is the initial light emission amount P ₀ , P ₀ can be expressed as the following formula (F-2). “C” and “D” are constants, and the constant “D” is a value obtained in advance.

P (T _j ) = C + D · T _j (F−1)
P ₀ = C + D · T ₀ (F-2)

  And the following formula | equation (F-3) is obtained from a formula (F-1) and a formula (F-2).

_{P (T j) -P 0 =} D (T j -T 0) (F-3)

  Furthermore, the following formula (G) can be obtained from the formula (F-3) and the formula (E).

P (T _j ) = P ₀ − (D / B) (V _f −V _f−0 ) (G)

In the lighting device control method or the liquid crystal display device assembly driving method according to the second aspect of the present invention, the initial light emission amount P ₀ and the initial forward voltage value are set by the light emitting element drive control circuit when the lighting device is started up. Measure _Vf-0 . Such an operation may be referred to as a “reference measurement mode”.

Further, at various atmospheric temperatures, an operation is performed such that various light emitting element driving currents flow for a predetermined time (for example, 5 microseconds) with respect to the light emitting elements having the same temperature as the atmospheric temperature. The relationship among _j , the forward voltage value _Vf , the light emission amount, and the light emitting element driving current is obtained in advance, and further, the value of the constant “D” is obtained.

On the other hand, the forward voltage value V _f is measured during operation of the illumination device or the planar light source device, that is, in the normal light emission mode. Then, the light emission amount P (T _j ) can be obtained based on the formula (G). Based on the light emission amount P (T _j ) at the junction temperature T _j thus obtained, or the initial light emission amount P ₀ , the initial forward voltage value V _f-0 and the forward voltage value V _f , Based on the obtained relationship between the junction temperature T _j , the forward voltage value V _f , the light emitting element driving current, and the light emission amount, the driving condition of the light emitting element, for example, the driving current for driving the light emitting element is determined. Can do. And a light emitting element is light-emitted by driving a light emitting element based on this determined drive condition. In addition, the above operation is performed by the light emitting element drive control circuit as described above.

  In the method of the present invention including the above-described preferred configurations and forms, a plurality of light emitting elements may be driven at the same time under the same driving conditions and under certain driving conditions. Alternatively, a plurality of light emitting elements may be partially driven (divided driving). That is, in an illuminating device or a planar light source device (hereinafter, these may be collectively referred to as “planar light source device etc.”), the display area of the liquid crystal display device is P × Q virtual display area units. It is composed of P × Q planar light source units corresponding to these P × Q display area units when it is assumed to be divided into two, and the light emission states of the P × Q planar light source units are individually controlled. It is good also as a form made.

  In the method of the present invention including the preferred configuration described above, the light emitting element can be composed of, for example, a light emitting diode (LED). In this case, a red light emitting diode that emits red light, a green light emitting diode that emits green light, and a blue light emitting diode that emits blue light can be configured as a set to obtain white light. White light can also be obtained by light emission of a light emitting diode that emits white light by combining an ultraviolet or blue light emitting diode and phosphor particles. Depending on the case, a light emitting diode that emits a fourth color other than red, green, blue, fifth color,... May be further provided.

  When the light emitting element is composed of a light emitting diode, for example, a red light emitting diode that emits red with a wavelength of 640 nm, for example, a green light emitting diode that emits green with a wavelength of 530 nm, and a blue light emitting diode that emits blue with a wavelength of 450 nm, for example, are assembled. As a combination of these, specifically, (one red light emitting diode, one green light emitting diode, one blue light emitting diode), (one red light emitting diode, two green light emitting diodes, one Blue light emitting diodes), (two red light emitting diodes, two green light emitting diodes, one blue light emitting diode), and the like.

  The light emitting diode constituting the light emitting element may have a so-called face-up structure or a flip chip structure. That is, the light-emitting diode includes a substrate and a light-emitting layer formed on the substrate, and may have a structure in which light is emitted from the light-emitting layer to the outside, or light from the light-emitting layer passes through the substrate. It is good also as a structure radiate | emitted outside. More specifically, the light emitting diode (LED) includes, for example, a first compound semiconductor layer having a first conductivity type (for example, n-type) formed on a substrate, and an active layer formed on the first compound semiconductor layer. A first electrode having a stacked structure of a second compound semiconductor layer having a second conductivity type (for example, p-type) formed on the active layer and electrically connected to the first compound semiconductor layer; A second electrode electrically connected to the two-compound semiconductor layer is provided. The layer constituting the light emitting diode may be made of a known compound semiconductor material depending on the emission wavelength.

  In the present invention, the planar light source device or the like may include a light diffusing plate or an optical function sheet in a portion facing the liquid crystal display device. Here, examples of the optical function sheet include a light diffusion sheet, a prism sheet, and a polarization conversion sheet including a reflective polarizing film having a multilayer structure. At least one of these sheets may be attached. Examples of the material constituting the light diffusion plate or the light diffusion sheet include polycarbonate resin (PC), polystyrene resin (PS), and methacrylic resin. A planar light source device or the like includes a housing. The housing may be made of, for example, plastic or metal, and has a kind of opening as a whole, a box having four side surfaces and one bottom surface. (A rectangular parallelepiped) member. And this opening part opposes a liquid crystal display device. A light emitting element may be attached to the bottom surface of the housing.

  When the plurality of light emitting elements are partially driven (divided drive), a partition wall may be provided between the planar light source unit and the planar light source unit. Specific examples of the material constituting the partition include polymethyl methacrylate resin (PMMA), polycarbonate resin (PC), polyarylate resin (PAR), polyethylene terephthalate resin (PET), acrylic resin, ABS resin, and glass. It can be mentioned, and it can be set as a transparent structure or an opaque structure with respect to the light radiate | emitted from the light emitting element with which the planar light source unit was equipped. A light diffusion reflection function may be imparted to the partition wall surface, or a specular reflection function may be imparted. In order to impart a light diffusing and reflecting function to the partition wall surface, irregularities may be formed on the partition wall surface based on a sandblasting method, or a film (light diffusion film) having irregularities may be attached to the partition wall surface. In addition, in order to impart a specular reflection function to the partition wall surface, a light reflection film may be attached to the partition wall surface, or a light reflection layer may be formed on the partition wall surface by plating, for example.

  The liquid crystal display device is preferably a transmissive liquid crystal display device having a display area composed of pixels arranged in a two-dimensional matrix. The transmissive liquid crystal display device includes, for example, a front panel having a transparent first electrode, a rear panel having a transparent second electrode, and a liquid crystal material disposed between the front panel and the rear panel. Consists of. The liquid crystal display device may be a monochrome liquid crystal display device or a color liquid crystal display device.

  More specifically, the front panel includes, for example, a first substrate made of, for example, a glass substrate or a silicon substrate, and a transparent first electrode (also called a common electrode, for example, ITO provided on the inner surface of the first substrate. And a polarizing plate (polarizing film / polarizing sheet) provided on the outer surface of the first substrate. Further, in the transmissive color liquid crystal display device, a color filter covered with an overcoat layer made of acrylic resin or epoxy resin is provided on the inner surface of the first substrate. Examples of the color filter arrangement pattern include a delta arrangement, a stripe arrangement, a diagonal arrangement, and a rectangle arrangement. The front panel further has a configuration in which a transparent first electrode is formed on the overcoat layer. An alignment film is formed on the transparent first electrode. On the other hand, the rear panel more specifically includes, for example, a second substrate made of a glass substrate or a silicon substrate, a switching element formed on the inner surface of the second substrate, and conduction / non-conduction by the switching element. A transparent second electrode to be controlled (also called a pixel electrode, made of, for example, ITO) and a polarizing plate (polarizing film / polarizing sheet) provided on the outer surface of the second substrate are configured. An alignment film is formed on the entire surface including the transparent second electrode. Various members and liquid crystal materials constituting the liquid crystal display device including these transmissive color liquid crystal display devices can be formed of known members and materials. Examples of the switching element include a three-terminal element such as a MOS type FET and a thin film transistor (TFT) formed on a single crystal silicon semiconductor substrate, and a two-terminal element such as an MIM element, a varistor element, and a diode.

  An area where the transparent first electrode and the transparent second electrode overlap and includes a liquid crystal cell corresponds to one pixel (pixel) or one sub-pixel (sub-pixel). In the transmissive color liquid crystal display device, the red light emitting sub-pixel (which may be referred to as sub-pixel [R]) constituting each pixel (pixel) transmits red light with the liquid crystal cell constituting the region. The green light emitting subpixel (sometimes referred to as subpixel [G]) is composed of a combination of a liquid crystal cell constituting the region and a color filter that transmits green light. The blue light-emitting subpixel (sometimes referred to as subpixel [B]) is composed of a combination of a liquid crystal cell that forms the region and a color filter that transmits blue light. The arrangement pattern of the sub-pixel [R], sub-pixel [G], and sub-pixel [B] matches the arrangement pattern of the color filter described above. The pixel is not limited to a configuration in which three types of sub-pixels [R, G, B], which are a sub-pixel [R], a sub-pixel [G], and a sub-pixel [B], are configured as one set. For example, a set of these three types of sub-pixels [R, G, B] plus one or more types of sub-pixels (for example, one sub-pixel that emits white light to improve brightness) To expand the color reproduction range, one set including sub-pixels that emit complementary colors to expand the color reproduction range, one set including sub-pixels that emit yellow to expand the color reproduction range It can also be composed of a set of subpixels that emit yellow and cyan.

  Here, the light transmittance (also referred to as aperture ratio) Lt of the pixel or sub-pixel, the luminance (display luminance) y of the display area corresponding to the pixel or sub-pixel, and the luminance (light source luminance) of the planar light source unit Y is defined as follows:

Y ₁ ... Is the maximum luminance of the light source luminance, for example, and may be hereinafter referred to as the light source luminance and the first specified value.
Lt ₁ ... Is the maximum value of the light transmittance (aperture ratio) of the pixels or sub-pixels in the display area unit, for example, and may be hereinafter referred to as light transmittance / first specified value.
Lt ₂ ... In the display area unit / input signal maximum value x _U which is the maximum value among the values of the input signals input to the liquid crystal display device driving circuit for driving all the pixels constituting the display area unit. The light transmittance (aperture ratio) of the pixel or sub-pixel when it is assumed that a control signal corresponding to an input signal having a value equal to _−max is supplied to the pixel or sub-pixel. Sometimes called a specified value. In addition, 0 ≦ Lt ₂ ≦ Lt ₁
y ₂ ... When the light source luminance is the light source luminance and the first specified value Y ₁ and the light transmittance (aperture ratio) of the pixel or sub-pixel is assumed to be the light transmittance and the second specified value Lt ₂ The display brightness obtained in the following is sometimes referred to as “display brightness / second prescribed value”.
Y ₂ ... ・ In the display area unit ・ Assuming that a control signal corresponding to an input signal having a value equal to the input signal maximum value x _U-max is supplied to the pixel or sub-pixel, Assuming that the light transmittance (aperture ratio) of the sub-pixel is corrected to the light transmittance / first prescribed value Lt ₁ , the luminance of the pixel or the sub-pixel is set to the display luminance / second prescribed value (y ₂ ). The light source brightness of the planar light source unit. However, the light source luminance Y ₂ may be corrected in consideration of the influence of the light source luminance of each planar light source unit on the light source luminance of other planar light source units.

When the planar light source device is partially driven (divided drive), it is assumed that a control signal corresponding to an input signal having a value equal to the input signal maximum value x _U-max in the display area unit is supplied to the pixel. The luminance of the light emitting elements constituting the planar light source unit corresponding to the display area unit is driven so that the luminance (light transmittance, display luminance at the first predetermined value Lt ₁ , second predetermined value y ₂ ) is obtained. Specifically, for example, the display luminance y ₂ can be obtained when the light transmittance (aperture ratio) of the pixel or the sub-pixel is set to, for example, the light transmittance / the first specified value Lt _1. In this way, the light source luminance Y ₂ may be controlled (for example, decreased). That is, for example, the light source luminance Y ₂ of the planar light source unit may be controlled for each image display frame so as to satisfy the following expression (1). Note that Y ₂ ≦ Y ₁ .

Y ₂ · Lt ₁ = Y ₁ · Lt ₂ (1)

When expressed in pixels arranged in a two-dimensional matrix the number M ₀ × N ₀ of _{(pixels) (M 0, N 0)} , the value of (M _0, N _0), specifically, VGA ( 640,480), S-VGA (800,600), XGA (1024,768), APRC (1152,900), S-XGA (1280,1024), U-XGA (1600,1200), HD-TV ( 1920, 1080), Q-XGA (2048, 1536), (1920, 1035), (720, 480), (1280, 960), etc. It is not limited to these values. Further, the relationship between the value of (M ₀ , N ₀ ) and the value of (P, Q) is not limited, but can be exemplified in Table 1 below. Examples of the number of pixels constituting one display area unit include 20 × 20 to 320 × 240, preferably 50 × 50 to 200 × 200. The number of pixels in the display area unit may be constant or different.

  The liquid crystal display device includes a liquid crystal display device driving circuit including a known circuit such as a timing controller. The luminance of the display area (display luminance) and the luminance of the planar light source unit (light source luminance) are controlled for each image display frame. Note that the number of image information (images per second) sent as electrical signals to the liquid crystal display device driving circuit per second is the frame frequency (frame rate), and the inverse of the frame frequency is the frame time (unit: second).

  The light emitting element drive control circuit and the liquid crystal display device drive circuit itself can be constituted by known circuits. The light emitting element drive control circuit may be composed of, for example, a light emitting element drive circuit, a light emitting element drive power supply, an arithmetic circuit, a storage device (memory), a forward voltage measurement circuit, a resistor, a light detection means, and the like. By connecting a resistor in series with the light emitting element, the forward current when a forward current is passed through the light emitting element can be measured. In addition, a forward voltage value can be obtained by measuring a potential difference between both ends of the light emitting element. Thermocouple, platinum resistance thermometer (platinum resistance thermometer), thermistor, IC temperature sensor (using transistor temperature characteristics), crystal thermometer (using crystal Y-cut) Can be illustrated. One temperature measuring unit may be provided for one light emitting element, one for a surface light source unit, or one for a whole surface light source device. Examples of the light detection means for measuring the amount of light emission include a known photo sensor such as a photodiode, a CCD device, and a CMOS sensor. One light detection means may be provided for one light emitting element, one for a planar light source unit, or one for a whole planar light source device or the like.

In the lighting device control method or the liquid crystal display device driving method according to the first aspect of the present invention, when the lighting device (planar light source device) is started up, the light emitting element drive control circuit serves as a reference measurement mode. The initial forward voltage value V _f-0 is measured, and at the same time, the initial ambient temperature T ₀ is measured by the temperature measuring means. That is, during the initial operation of the illumination device (planar light source device), a kind of calibration operation is performed in a state where the temperature of the light emitting element itself is equal to the ambient temperature. Then, during normal operation of the illumination device (planar light source device), as the normal light emission mode, the forward voltage value V _f is measured by the light emitting element drive control circuit, and the initial forward voltage value V _f-0 , the forward direction is measured. Based on the voltage value V _f and the initial ambient temperature T ₀ , the driving conditions of the light emitting element are determined. Therefore, even _if an irreversible temporal variation of the forward voltage value V _f occurs, a kind of calibration operation is performed during the initial operation of the illumination device (planar light source device), so that the illumination device (planar light source device) In the normal operation, an operation state in which the irreversible temporal variation of the forward voltage value V _f is compensated can be obtained. Therefore, it is possible to suppress fluctuations in color temperature and luminance due to irreversible temporal fluctuations in the forward voltage value _Vf , and to control color irregularities, luminance irregularities, color deviations, and luminance deviations in a liquid crystal display device with high accuracy. It becomes possible to do.

In the lighting device control method or the liquid crystal display device assembly driving method according to the second aspect of the present invention, when the lighting device (planar light source device) is started up, the light emitting element drive control circuit serves as a reference measurement mode. The initial light emission amount P ₀ and the initial forward voltage value V _f-0 are measured. That is, during the initial operation of the illumination device (planar light source device), a kind of calibration operation is performed in a state where the temperature of the light emitting element itself is equal to the ambient temperature. When the illumination device (planar light source device) is operated, the forward voltage value V _f is measured by the light emitting element drive control circuit as the normal light emission mode, and the initial light emission amount P ₀ and the initial forward voltage value V _f− are measured. _{Based on 0} and the forward voltage value _Vf , the driving condition of the light emitting element is determined. Therefore, even if an irreversible change in the amount of light emission occurs, a normal operation of the illumination device (planar light source device) is performed because a kind of calibration operation is performed during the initial operation of the illumination device (planar light source device). In some cases, an operating state in which an irreversible change in the light emission amount of the light emitting element is compensated can be obtained. Accordingly, variations in color temperature and luminance due to irreversible changes in the light emission amount of the light emitting element can be suppressed, and color unevenness, luminance unevenness, color shift, and brightness shift in a liquid crystal display device can be controlled with high accuracy. It becomes possible.

  Hereinafter, the present invention will be described based on examples with reference to the drawings.

  Example 1 relates to a method for controlling a lighting device and a method for driving a liquid crystal display device assembly according to the first aspect of the present invention. A circuit diagram of a liquid crystal display device assembly or a lighting device comprising a color liquid crystal display device and a planar light source device in Embodiment 1 or Embodiments 2 to 4 described later is shown in FIGS. Shown in B). A conceptual diagram including a light emitting element drive control circuit of the liquid crystal display device assembly is shown in FIG. 2, and a conceptual diagram of the light emitting element drive control circuit is shown in FIG. Furthermore, FIG. 4A schematically shows the arrangement and arrangement of light emitting elements and the like in the surface light source devices of Example 1 or Examples 2 to 4 described later, and a color liquid crystal display device and FIG. 4B shows a schematic partial cross-sectional view of a liquid crystal display device assembly including a planar light source device. FIG. 5 shows a schematic partial cross-sectional view of the color liquid crystal display device. In FIGS. 1A and 1B, the signal flow is indicated by a single line segment, and the current flow is indicated by a double line segment.

The liquid crystal display device assembly of Example 1 or Example 2 to Example 4 to be described later is
(A) a liquid crystal display device (more specifically, a transmissive color liquid crystal display device 10 having a display region composed of pixels arranged in a two-dimensional matrix), and
(B) a planar light source device 20 for illuminating the color liquid crystal display device 10 from the back surface;
It has.

And the planar light source device 20 of Example 1 or the illuminating device 20 of Example 1 (hereinafter referred to as the planar light source device 20) is:
(A) Light emitting element 22,
(B) a light emitting element drive control circuit 90 for supplying a current to the light emitting element 22 and measuring the forward voltage value of the light emitting element 22, and
(C) temperature measuring means 70 for measuring the ambient temperature around the light emitting element 22;
It has.

  Here, the planar light source device 20 of the first embodiment or the second to fourth embodiments described later includes a plurality of planar light source units 21 each composed of a plurality of light emitting elements 22. One temperature measuring means 70 is provided for the plurality of light emitting elements 22 (specifically, for one planar light source unit 21). The configuration and structure of the planar light source device are not limited to such a configuration and structure, and various modifications can be made.

  Specifically, when the display area 11 of the color liquid crystal display device 10 is assumed to be divided into P × Q virtual display area units 12, P × corresponding to these P × Q display area units 12. A planar light source device 20 is constituted by Q planar light source units 21, and the light emission states of the P × Q planar light source units 21 are individually controlled. That is, a so-called partial driving method (divided driving method) in which the plurality of light emitting elements 22 are partially driven (divided driving) is employed. However, the present invention is not limited to such a surface light source device, and a method of driving a plurality of light emitting elements simultaneously under the same driving conditions may be employed.

  In Example 1 or Example 2 to Example 4 described later, a light emitting diode (LED) is used as the light emitting element 22 constituting the planar light source device 20. The light emitting element as the light source includes a red light emitting element (red light emitting diode) 22R that emits red (for example, dominant wavelength 640 nm), a green light emitting element (green light emitting diode) 22G that emits green (for example, dominant wavelength 530 nm), and , And a blue light emitting element (blue light emitting diode) 22B that emits blue light (for example, dominant wavelength 450 nm). The combination of light emitting elements constituting one planar light source unit 21 (sometimes referred to as light source 21A) is, for example, (one red light emitting element 22R, two green light emitting elements 22G, and one blue light emitting element 22B). ).

  Hereinafter, the transmissive color liquid crystal display device 10, the planar light source device 20, the light emitting element drive control circuit 90, etc. in Embodiment 1 or Embodiments 2 to 4 described later will be described with reference to FIGS. (A) and (B) will be described with reference to FIG.

As shown in the conceptual diagram of FIG. 2, the transmissive color liquid crystal display device 10 has a total of M ₀ × N ₀ , M ₀ pieces along the first direction and N ₀ pieces along the second direction. Are provided with a display region 11 arranged in a two-dimensional matrix. Here, it is assumed that the display area 11 is divided into P × Q virtual display area units 12. Each display area unit 12 is composed of a plurality of pixels. Specifically, for example, the image display resolution satisfies the HD-TV standard, and the number M ₀ × N ₀ of pixels (pixels) arranged in a two-dimensional matrix is expressed as (M ₀ , N ₀ ). For example, (1920, 1080). In addition, a display area 11 (indicated by a one-dot chain line in FIG. 2) composed of pixels arranged in a two-dimensional matrix is divided into P × Q virtual display area units 12 (indicated by a dotted line). ing. The value of (P, Q) is (19, 12), for example. However, in order to simplify the drawing, the number of display area units 12 (and planar light source units 21) in FIG. 2 is different from this value. Each display area unit 12 is composed of a plurality of (M × N) pixels, and the number of pixels constituting one display area unit 12 is, for example, about 10,000. Each pixel is configured as a set of a plurality of sub-pixels that emit different colors. More specifically, each pixel has three types of red light emitting subpixel (subpixel [R]), green light emitting subpixel (subpixel [G]), and blue light emitting subpixel (subpixel [B]). Of sub-pixels (sub-pixels). The transmissive color liquid crystal display device 10 is line-sequentially driven. More specifically, the color liquid crystal display device 10 includes scan electrodes (extending along the first direction) and data electrodes (extending along the second direction) that intersect in a matrix. Then, a scanning signal is input to the scanning electrode to select and scan the scanning electrode, and an image is displayed based on the data signal (a signal based on the control signal) input to the data electrode to constitute one screen.

  As shown in the schematic partial cross-sectional view of FIG. 5, the color liquid crystal display device 10 includes a front panel 50 having a transparent first electrode 54, a rear panel 60 having a transparent second electrode 64, and The liquid crystal material is disposed between the front panel 50 and the rear panel 60.

  The front panel 50 includes, for example, a first substrate 51 made of a glass substrate and a polarizing film 56 provided on the outer surface of the first substrate 51. A color filter 52 covered with an overcoat layer 53 made of acrylic resin or epoxy resin is provided on the inner surface of the first substrate 51, and a transparent first electrode (also called a common electrode) is formed on the overcoat layer 53. (Made of, for example, ITO) 54 is formed, and an alignment film 55 is formed on the transparent first electrode 54. On the other hand, the rear panel 60 more specifically includes, for example, a second substrate 61 made of a glass substrate, and switching elements (specifically, thin film transistors and TFTs) formed on the inner surface of the second substrate 61. 62, a transparent second electrode (also referred to as a pixel electrode, made of, for example, ITO) 64 whose conduction / non-conduction is controlled by the switching element 62, and a polarizing film 66 provided on the outer surface of the second substrate 61, It is composed of An alignment film 65 is formed on the entire surface including the transparent second electrode 64. The front panel 50 and the rear panel 60 are joined to each other at their outer peripheral portions via a sealing material (not shown). Note that the switching element 62 is not limited to a TFT, and may be composed of, for example, an MIM element. Reference numeral 67 in the drawing is an insulating layer provided between the switching element 62 and the switching element 62.

  Since various members and liquid crystal materials constituting these transmissive color liquid crystal display devices can be composed of well-known members and materials, detailed description thereof is omitted.

  As described above, the direct-type planar light source device (backlight) 20 includes P × Q planar light source units 21 corresponding to P × Q virtual display area units 12, and each planar light source. The unit 21 illuminates the display area unit 12 corresponding to the planar light source unit 21 from the back side. The light emitting elements 22 provided in the planar light source unit 21 are individually controlled. However, the light source luminance of the planar light source unit 21 is not affected by the light emitting state of the light emitting elements 22 provided in the other planar light source units 21. Although the planar light source device 20 is located below the color liquid crystal display device 10, the color liquid crystal display device 10 and the planar light source device 20 are separately displayed in FIG. The arrangement and arrangement of light emitting elements and the like in the planar light source device 20 are schematically shown in FIG. 4A, and a schematic one of the liquid crystal display device assembly comprising the color liquid crystal display device 10 and the planar light source device 20 is shown. A partial cross-sectional view is shown in FIG. The light emitting element 22 is driven based on a pulse width modulation (PWM) control method. The luminance of the planar light source unit 21 is increased / decreased by duty ratio increasing / decreasing control in the pulse width modulation control of the light emitting elements 22 constituting the planar light source unit 21.

  As shown in the schematic partial cross-sectional view of the liquid crystal display device assembly in FIG. 4B, the planar light source device 20 includes a casing 31 having an outer frame 33 and an inner frame 34. Yes. The end of the transmissive color liquid crystal display device 10 is held by the outer frame 33 and the inner frame 34 so as to be sandwiched between the spacers 35A and 35B. A guide member 36 is disposed between the outer frame 33 and the inner frame 34 so that the color liquid crystal display device 10 sandwiched between the outer frame 33 and the inner frame 34 does not shift. A light diffusing plate 41 is attached to the inner frame 34 via a spacer 35C and a bracket member 37 inside and above the casing 31. On the light diffusion plate 41, an optical function sheet group such as a light diffusion sheet 42, a prism sheet 43, and a polarization conversion sheet 44 is laminated.

  A reflection sheet 45 is provided inside and below the housing 31. Here, the reflection sheet 45 is disposed so that the reflection surface thereof faces the light diffusion plate 41, and is attached to the bottom surface 32 </ b> A of the housing 31 via an attachment member (not shown). The reflection sheet 45 can be composed of, for example, a silver-enhanced reflection film having a structure in which a silver reflection film, a low refractive index film, and a high refractive index film are sequentially laminated on a sheet base material. The reflection sheet 45 reflects light emitted from the plurality of light emitting elements 22 or light reflected by the side surface 32B of the housing 31 or the partition wall 23 shown in FIG. Thus, red light, green light, and blue light emitted from the red light emitting element 22R that emits red light, the green light emitting element 22G that emits green light, and the blue light emitting element 22B that emits blue light are mixed, and the color purity is high. White light can be obtained as illumination light. The illumination light is emitted from the planar light source unit 21 through the light diffusion plate 41, passes through the optical function sheet group such as the light diffusion sheet 42, the prism sheet 43, and the polarization conversion sheet 44, and the color liquid crystal display device 10 is moved to the back surface. Illuminate from.

  In the vicinity of the bottom surface 32 </ b> A of the housing 31, photodiodes that are the light detection means 71 (71 </ b> R, 71 </ b> G, 71 </ b> B) are arranged. The light detection means measures the light emission amount (luminance) and chromaticity of the light emitting elements 22R, 22G, and 22B.

  As shown in FIGS. 2 and 3, the driving circuit for driving the planar light source device 20 and the color liquid crystal display device 10 based on an input signal from the outside (display circuit) is based on the pulse width modulation control method. Light source device control circuit 80 and light emitting device drive control circuit 90 for performing on / off control of the red light emitting element 22, the green light emitting element 22G, and the blue light emitting element 22B constituting the planar light source device 20, and a liquid crystal display device The driving circuit 85 is configured.

  The planar light source device control circuit 80 includes an arithmetic circuit 81 and a storage device (memory) 82. On the other hand, the light emitting element drive control circuit 90 includes an initial pulse generation circuit 91, a timer 92, a switch 93, a light emitting element drive circuit 94, a forward voltage measuring circuit 95, a light emitting element drive power source (constant current source) 96, and a switching circuit including FETs. A control switch 97 (97R, 97G, 97B) composed of elements, a resistor 98 (98R, 98G, 98B), and light detection means 71 (71R, 71G, 71B) are configured. These circuits and the like constituting the planar light source device control circuit 80 and the light emitting element drive control circuit 90 can be known circuits. On the other hand, a liquid crystal display device driving circuit 85 for driving the color liquid crystal display device 10 is configured by a known circuit such as a timing controller 86. The color liquid crystal display device 10 is provided with a gate driver, a source driver, and the like (not shown) for driving a switching element 62 composed of a TFT constituting a liquid crystal cell.

Hereinafter, the control method of the illumination device or the driving method of the liquid crystal display device assembly according to the first embodiment will be described. In the first embodiment, the forward voltage value V _f associated with the long-time aging of the light emitting element 22 will be described. Compensates for irreversible fluctuations. In the first embodiment, as a method for controlling the luminance of the light emitting element 22 to be constant, a method for controlling the number of pulses when the light emitting element 22 is driven based on the PWM control method is employed.

In the control method of the illumination device or the driving method of the liquid crystal display device assembly of the first embodiment, the calibration operation is first performed when the planar light source device 20 is started up, that is, in the reference measurement mode. That is, the initial forward voltage value V _f-0 is measured by the light emitting element drive control circuit 90, and the initial ambient temperature T ₀ is measured by the temperature measuring means.

Specifically, as shown in FIG. 1A, immediately after the planar light source device 20 is powered on, a reference pulse is applied to the light emitting element 22 before starting the illumination of the liquid crystal display device. When the planar light source device 20 is started up, the light emitting element 22 is equal to the ambient temperature (initial ambient temperature T ₀ ). The time length of the reference pulse is set to such a length that the heat generation of the light emitting device can be ignored. Specifically, the reference pulse has an initial drive current value I ₀ of, for example, 200 mA, and the time length is, for example, 5 microseconds. By applying such a reference pulse, the temperature of the light emitting element 22 does not increase. Accordingly, the ambient temperature (initial ambient temperature T ₀ ) at this time can be regarded as the junction temperature T _j .

More specifically, as shown in FIG. 1A, the initial pulse generation circuit 91 and the light emitting element driving circuit 94 are connected by a switch 93. An initial pulse is generated in the initial pulse generation circuit 91, and the initial pulse is sent to the light emitting element driving circuit 94. Based on the initial pulse, the light emitting element drive circuit 94 determines the on time t _ON and the off time t _OFF of the light emitting element 22. A current flowing through the light emitting element 22 obtained by a combination of the on time t _ON and the off time t _OFF is a reference pulse. On the other hand, the light emitting element driving circuit 94 sends a signal to the light emitting element driving power source 96 to flow the initial driving current value I ₀ . From the light emitting element driving power source 96, an initial driving current value I ₀ (specifically, for example, 200 mA) for driving the light emitting element 22 is supplied. Then, under the control of the light emitting element driving circuit 94, the control switch 97 is turned on / off based on the on time t _ON and the off time t _OFF . The total sum of the on time t _ON and the off time t _OFF is, for example, 5 microseconds. Then, the value of the potential difference across the light emitting element 22 based on the initial drive current value I ₀ at this time is measured by the forward voltage measurement circuit 95 as the initial forward voltage value V _f-0 , and the initial forward voltage value V _f-0 is sent to the light emitting element driving circuit 94. In addition, the ambient temperature (initial ambient temperature T ₀ ) at this time is measured by the temperature measuring means 70. The temperature measurement data is also sent to the light emitting element driving circuit 94. Thus, in the light emitting element driving circuit 94, the value of the coefficient “A” in the equation (D) can be obtained. The value of the constant “B” obtained in advance is stored in the storage device 82. Then, the obtained value of the coefficient “A” is stored in the storage device 82. The forward voltage value V _f varies irreversibly due to the aging of the light emitting element 22. Such an irreversible variation is caused by variation in the value of the coefficient “A” in the equation (D). Therefore, the value of the coefficient “A” in the equation (D) is obtained by the calibration operation, so that the light emission state of the light emitting element 22 during the operation of the planar light source device 20 (in the normal light emission mode) is compensated. Can do. The above operation is performed on the red light emitting element 22R, the green light emitting element 22G, and the blue light emitting element 22B, and the value of the coefficient “A” in each of the red light emitting element 22R, the green light emitting element 22G, and the blue light emitting element 22B is obtained. .

When the planar light source device 20 is in operation (in the normal light emission mode), the forward voltage value V _f is measured by the light emitting element drive control circuit 90 as shown in FIG. Based on the value V _f-0 , the forward voltage value V _f, and the initial ambient temperature T ₀ , the driving condition of the light emitting element 22 is determined. Specifically, the drive current for driving the light emitting element 22 is determined. Then, the light emitting element 22 is driven with the determined drive current.

Specifically, at the start of the operation of the planar light source device 20, for example, the light emitting element 22 is driven by the initial drive current value I ₀ at the same level as that at the time of calibration. The amount of light corresponding to the drive current value I ₀ is output. Then, when the operation of the planar light source device 20 is continued and the initial drive current value I ₀ continues to flow through the light emitting element 22, the temperature of the light emitting element 22 rises due to the heat generation of the light emitting element 22, and the junction temperature T _j Rises. As a result, the light emission characteristics of the light emitting element 22 vary. Specifically, in the light emitting element 22, the amount of light emission decreases, and the dominant wavelength changes to the long wavelength side. Therefore, the value of the potential difference across the light emitting element 22 based on the initial drive current value I ₀ is measured in the forward voltage measurement circuit 95 as a forward voltage V _f, the forward voltage V _f emitting element driving circuit 94 Is sent out. In addition, the ambient temperature T at this time is measured by the temperature measuring means 70 for reference, and the temperature measurement data is sent to the light emitting element driving circuit 94. Thus, in the light emitting element driving circuit 94, the value of the formula (E), that is,
T _j = T ₀ − (V _f −V _f−0 ) / B (E)
(Where B is a constant determined in advance), and the driving current is determined based on the determined value. Specifically, in the light emitting element driving circuit 94, the value of the junction temperature T _j can be obtained based on the formula (E). Based on the value of the junction temperature T _j, the light emission amount and the dominant wavelength are obtained in advance so as to obtain the same light emission amount and dominant wavelength as when the initial drive current value I ₀ was passed through the light emitting element 22 at the start of the operation of the planar light source device 20. The driving current for driving the light emitting element 22 based on the relationship between the junction temperature T _j , the forward voltage value V _f, and the light emitting element driving current (these relationships are stored in the storage device 82). And the light emitting element 22 is driven with the determined drive current. The difference between the ambient temperature T and the junction temperature T _j is determined by the product of the thermal resistance value of the light emitting element 22 and the amount of heat generated. Therefore, by measuring the normal thermal resistance value in advance and storing it in the storage device 82, for example, by measuring the atmospheric temperature T, it is possible to detect an abnormality.

More specifically, as shown in FIG. 1B, a pulse width modulation output signal (described later) is sent from the planar light source device control circuit 80 to the light emitting element driving circuit 94 via the switch 93. In the light emitting element driving circuit 94, the on time t _ON and the off time t _{OFF of} the light emitting element 22 are determined based on the pulse width modulation output signal. A driving current for driving the light emitting element 22 is added to the on time t _ON and the off time t _OFF . Specifically, the on-time t _ON and the off-time t _OFF are increased based on the determined drive current (more specifically, the integrated value of the drive current) to be passed through the light emitting element 22 described above. The value of current supplied from the light emitting element driving power supply 96 for driving the light emitting element 22 is an initial driving current value I ₀ . Then, under the control of the light emitting element driving circuit 94, the control switch 97 is turned on / off based on the on time t _ON and the off time t _OFF (Total _ON '), and the light emitting element 22 emits light. The control of Total _ON ′ may be performed for each image display frame, or may be performed for each predetermined number of image display frames. This state is shown in FIG. By increasing the duty ratio as the junction temperature T _j increases, the luminance of the light emitting element 22 can be controlled to be constant. In FIG. 6, Δt _W represents the time length of the reference measurement mode, Δt _L represents the time length of one image display frame, and Δt _s measured the forward voltage value V _f in the normal light emission mode. It indicates it is _{time, Δt p0, Δt p1, Δt} p2, Δt p3 denotes a period during which the light emitting element 22 is emitting light (the sum total total _oN on-time t _oN and oFF time t _oFF ').

  Hereinafter, the normal light emission operation of the planar light source device 20, that is, the light emission operation in the normal light emission mode of the planar light source unit 21 will be described.

  By the way, the display area 11 composed of pixels arranged in a two-dimensional matrix is divided into P × Q display area units. This state is expressed by “row” and “column”. It can be said that the display area unit is divided into rows × P columns. The display area unit 12 is composed of a plurality of (M × N) pixels. When this state is expressed by “row” and “column”, it is composed of pixels of N rows × M columns. I can say. Further, the red light emitting subpixel (subpixel [R]), the green light emitting subpixel (subpixel [G]), and the blue light emitting subpixel (subpixel [B]) are collectively collected as “subpixel [ R, G, B] ”and may be referred to as“ sub-pixel ”for controlling the operation of the sub-pixel [R, G, B] (specifically, for example, controlling the light transmittance (aperture ratio)). The red light emitting subpixel / control signal, the green light emitting subpixel / control signal, and the blue light emitting subpixel / control signal input to [R, G, B] are collectively referred to as “control signal [R, G, B] ”, and is inputted from the outside to the planar light source device control circuit 80 and the liquid crystal display device driving circuit 85 in order to drive the sub-pixels [R, G, B] constituting the display region unit. Collect the red light emitting subpixel / input signal, green light emitting subpixel / input signal, and blue light emitting subpixel / input signal together. Which may force signals [R, G, B] and "called.

As described above, each pixel includes a red light emitting subpixel (red light emitting subpixel, subpixel [R]), a green light emitting subpixel (green light emitting subpixel, subpixel [G]), and a blue light emitting subpixel ( The blue light emitting subpixel and the subpixel [B]) are configured as a set of three subpixels (subpixels). In the following description, it is assumed that the luminance control (gradation control) of each of the sub-pixels [R, G, B] is 8-bit control, and is performed in 2 ⁸ steps from 0 to 255. Therefore, the value of the input signal [R, G, B] input to the liquid crystal display device drive circuit 85 to drive each of the sub-pixels [R, G, B] in each pixel constituting each display area unit 12. x _R, x _G, each x _B, takes a value of 2 ⁸ steps. Further, pulse width modulation output signal values S _R , S _G , S _B for controlling the respective light emission times of the red light emitting element 22R, the green light emitting element 22G and the blue light emitting element 22B constituting each planar light source unit 21. also takes a value of 2 ⁸ steps of 0 to 255. However, the present invention is not limited to this. For example, 10-bit control can be performed in 2 ¹⁰ stages from 0 to 1023. In this case, if an 8-bit numerical expression is multiplied by, for example, 4 times Good.

A control signal for controlling the light transmittance Lt of each pixel is supplied from the liquid crystal display device driving circuit 85 to each pixel. Specifically, a control signal [R, G, B] for controlling the light transmittance Lt of each of the sub-pixels [R, G, B] is transmitted to each of the sub-pixels [R, G, B]. Supplied from the drive circuit 85. That is, in the liquid crystal display device driving circuit 85, the control signals [R, G, B] are generated from the input signals [R, G, B], and the control signals [R, G, B] are subpixels. [R, G, B] are supplied (output). Since the light source luminance Y ₂ which is the luminance of the planar light source unit 21 is changed for each image display frame, the control signal [R, G, B] is, for example, the value of the input signal [R, G, B]. Values X _R-corr , X _G-corr , and X _B-corr obtained by performing correction (compensation) based on changes in the light source luminance Y _{2 with} respect to the values obtained by raising x _R , x _G , and x _B to the power of 2.2 Have. Then, the control signal [R, G, B] is sent from the timing controller 86 constituting the liquid crystal display device driving circuit 85 to the gate driver and source driver of the color liquid crystal display device 10 by a known method. Based on [R, G, B], the switching element 62 constituting each subpixel is driven, and a desired voltage is applied to the transparent first electrode 54 and the transparent second electrode 64 constituting the liquid crystal cell. The light transmittance (aperture ratio) Lt of the sub-pixel is controlled. Here, the larger the values X _R-corr , X _G-corr , and X _B-corr of the control signal [R, G, B], the light transmittance (aperture ratio) Lt of the sub-pixel [R, G, B]. And the value of the luminance (display luminance y) of the display area corresponding to the sub-pixel [R, G, B] increases. That is, an image composed of light passing through the sub-pixels [R, G, B] (usually a kind of dot) is bright.

The display brightness y and the light source brightness Y ₂ are controlled for each image display frame, each display area unit, and each planar light source unit in the image display of the color liquid crystal display device 10. The operation of the color liquid crystal display device 10 and the operation of the planar light source device 20 within one image display frame are synchronized. The number of image information (images per second) sent to the liquid crystal display device drive circuit 85 as electrical signals per second is the frame frequency (frame rate), and the inverse of the frame frequency is the frame time (unit: second).

  Hereinafter, the driving method of the liquid crystal display device assembly in Example 1 or Examples 2 to 4 to be described later will be described with reference to FIGS. FIG. 7 is a flowchart for explaining a driving method of the liquid crystal display device assembly according to the first embodiment.

In Embodiment 1 or Embodiments 2 to 4 to be described later, a control signal for controlling the light transmittance Lt of each pixel is supplied from the liquid crystal display device driving circuit 85 to each pixel. More specifically, a control signal [R, G, B] that controls the light transmittance Lt of each of the sub-pixels [R, G, B] is supplied to each of the sub-pixels [R, G, B] constituting each pixel. B] is supplied from the liquid crystal display device driving circuit 85. In each of the planar light source units 21, input signals [input to the drive circuits 80 and 85 to drive all the pixels (sub-pixels [R, G, B]) constituting each display area unit 12 [ The control signal corresponding to the input signal having a value equal to the in _- display area unit input signal maximum value x _U-max that is the maximum value among the values x _R , x _G , x _B of R, G, B] So that the brightness (light transmittance, display brightness at the first specified value Lt ₁ , second specified value y ₂ ) of the pixel (sub-pixel [R, G, B]) is assumed to be supplied to The luminance of the light source 21A constituting the planar light source unit 21 corresponding to the display area unit 12 is controlled by the planar light source device control circuit 80 and the light emitting element drive control circuit 90. Specifically, for example, the light source luminance Y ₂ is obtained so that the display luminance y ₂ can be obtained when the light transmittance (aperture ratio) of the pixel or the sub-pixel is, for example, the light transmittance · the first specified value Lt _1. May be controlled (for example, decreased). That is, for example, the light source luminance Y ₂ of the planar light source unit 21 may be controlled for each image display frame so as to satisfy the following expression (1). Note that Y ₂ ≦ Y ₁ .

Y ₂ · Lt ₁ = Y ₁ · Lt ₂ (1)

[Step-100]
An input signal [R, G, B] and a clock signal CLK for one image display frame sent from a known display circuit such as a scan converter are input to the planar light source device control circuit 80 and the liquid crystal display device drive circuit 85. (See FIG. 2). Note that the input signals [R, G, B] are output signals from the image pickup tube, for example, when the input light quantity to the image pickup tube is y ′, and are output from, for example, a broadcasting station and the light transmittance Lt of the pixel. Is an input signal that is also input to the liquid crystal display device driving circuit 85, and can be expressed by a function of the input light quantity y ′ to the power of 0.45. The values x _R , x _G , x _B of the input signals [R, G, B] for one image display frame input to the surface light source device control circuit 80 constitute the surface light source device control circuit 80. The data is temporarily stored in the storage device 82. Further, the values x _R , x _G , x _B of the input signals [R, G, B] for one image display frame inputted to the liquid crystal display device driving circuit 85 are also stored in the liquid crystal display device driving circuit 85. (Not shown) once stored.

[Step-110]
Next, in the arithmetic circuit 81 constituting the surface light source device control circuit 80, the value of the input signal [R, G, B] stored in the storage device 82 is read, and the (p, q) th [however, first , P = 1, q = 1] for driving the sub-pixels [R, G, B] in all the pixels constituting the (p, q) -th display region unit 12 In the display circuit unit, the input signal maximum value x _U-max , which is the maximum value among the values x _R , x _G , x _B of the input signals [R, G, B], is obtained by the arithmetic circuit 81. Then, the display area unit / input signal maximum value x _U-max is stored in the storage device 82. This step is executed for all of m = 1, 2,..., M, n = 1, 2,..., N, that is, for M × N pixels.

For example, when x _R is a value corresponding to “110”, x _G is a value corresponding to “150”, and x _B is a value corresponding to “50”, x _U-max is “150”. Is a value corresponding to.

This operation is repeated from (p, q) = (1, 1) to (P, Q), and the display area unit internal input signal maximum value x _U-max in all the display area units 12 is stored in the storage device 82. Remember.

[Step-120]
Then, the control signal [R, G, B] corresponding to the input signal [R, G, B] having a value equal to the maximum value x _U-max in the display area unit is sub-pixel [R, G, B]. ] Corresponding to the display area unit 12 so that the brightness (light transmittance, display brightness at the first specified value Lt ₁ , second specified value y ₂ ) is obtained by the planar light source unit 21. The light source luminance Y ₂ of the planar light source unit 21 is increased or decreased under the control of the light emitting element drive control circuit 90. Specifically, the light source luminance Y ₂ may be controlled for each image display frame and for each planar light source unit so as to satisfy the following expression (1). More specifically, the luminance of the light emitting element 22 is controlled based on the equation (2) that is the light source luminance control function g (x _nol-max ), and the light source luminance Y ₂ is set so as to satisfy the equation (1). Control is sufficient. A conceptual diagram of such control is shown in FIGS. 9A and 9B. However, as will be described later, correction based on the influence of the other planar light source unit 21 is performed on the light source luminance Y ₂ as necessary. It should be noted that these relations regarding the control of the light source luminance Y ₂ , that is, the value of the control signal corresponding to the input signal having a value equal to the maximum value x _U-max in the display area unit and the input signal maximum value x _U-max . , The display luminance when assuming that such a control signal is supplied to the pixel (sub-pixel), the second specified value y ₂ , the light transmittance (aperture ratio) of each sub-pixel at this time [light transmittance / first 2 specified value Lt ₂ ], and a planar light source that provides display luminance and second specified value y ₂ when the light transmittance (aperture ratio) of each sub-pixel is set to light transmittance and first specified value Lt _1. The relationship of the brightness control parameters in the unit 21 may be obtained in advance and stored in the storage device 82 or the like.

Y ₂ · Lt ₁ = Y ₁ · Lt ₂ (1)
g (x _nol-max ) = a ₁ · (x _nol-max ) ^2.2 + a ₀ (2)

Here, input signals (input signals [R, G, B]) that are input to the liquid crystal display driving circuit 85 to drive the pixels (or the sub-pixels [R, G, B] constituting the pixels). ) _Is the maximum value x _max
x _nol-max ≡ x _U-max / x _max
And a ₁ and a ₀ are constants,
a ₁ + a ₀ = 1
0 <a ₀ <1, 0 <a ₁ <1
Can be expressed as For example,
a ₁ = 0.99
a ₀ = 0.01
And it is sufficient. The value x _R, x _G of the input signal [R, G, B], each x _B, and takes a value of 2 ⁸ steps, the value of x _max is a value corresponding to "255".

  By the way, in the planar light source device 20, for example, assuming brightness control of the planar light source unit 21 of (p, q) = (1, 1), other P × Q planar light source units. It may be necessary to consider the effects from 21. Since the influence that the planar light source unit 21 receives from the other planar light source units 21 is known in advance by the light emission profile of each planar light source unit 21, the difference can be calculated by back calculation, and as a result, the correction is performed. Is possible. The basic form of calculation will be described below.

The luminance (light source luminance Y ₂ ) required for the P × Q planar light source units 21 based on the requirements of the equations (1) and (2) is represented by a matrix [L _PxQ ]. Further, the luminance of a certain planar light source unit obtained when only a certain planar light source unit is driven and the other planar light source units are not driven is compared with P × Q planar light source units 21. Obtain in advance. Such luminance is represented by a matrix [L ′ _PxQ ]. Further, the correction coefficient is represented by a matrix [α _PxQ ]. Then, the relationship between these matrices can be expressed by the following equation (3-1). The correction coefficient matrix [α _PxQ ] can be obtained in advance.
[L _PxQ ] = [L ′ _PxQ ] · [α _PxQ ] (3-1)
Therefore, what is necessary is just to obtain | _require matrix [L' _PxQ ] from Formula (3-1). The matrix [L ′ _PxQ ] can be obtained from the inverse matrix operation. That is,
[L ′ _PxQ ] = [L _PxQ ] · [α _PxQ ] ⁻¹ (3-2)
Should be calculated. Then, the light source 21A (light emitting element 22) provided in each planar light source unit 21 may be controlled so that the luminance represented by the matrix [L ′ _PxQ ] can be obtained. The processing may be performed using information (data table) stored in a storage device (memory) (not shown). In the control of the light emitting element 22, the value of the matrix [L ′ _PxQ ] cannot take a negative value, and needless to say, the calculation result needs to be kept in a positive region. Therefore, the solution of equation (3-2) may not be an exact solution but an approximate solution.

As described above, the matrix [L _PxQ ] obtained based on the values of the equations (1) and (2) obtained in the arithmetic circuit 81 constituting the surface light source device control circuit 80, and the matrix [α _PxQ ] of the correction coefficient. ], As described above, the luminance matrix [L ′ _PxQ ] when it is assumed that the planar light source unit is driven alone is obtained, and further, 0 to 0 based on the conversion table stored in the storage device 82. Convert to a corresponding integer (value of the pulse width modulation output signal) in the range of 255. Thus, in the arithmetic circuit 81 constituting the planar light source device control circuit 80, the value S _R of the pulse width modulation output signal for controlling the light emission time of the red light emitting element 22R in the planar light source unit 21, the green light emitting element 22G The value S _G of the pulse width modulation output signal for controlling the light emission time and the value S _B of the pulse width modulation output signal for controlling the light emission time of the blue light emitting element 22B can be obtained.

[Step-130]
Next, the values S _R , S _G , and S _B of the pulse width modulation output signal obtained in the arithmetic circuit 81 constituting the planar light source device control circuit 80 are light emission provided corresponding to the planar light source unit 21. The data is sent to a storage device (not shown) of the element drive control circuit 90 and stored in this storage device. The clock signal CLK is also sent to the light emitting element drive control circuit 90 (see FIG. 3).

[Step-140]
Based on the values S _R , S _G , and S _B of the pulse width modulation output signal, the on time t _R-ON and the off time t _{R-OFF of} the red light emitting element 22R constituting the planar light source unit 21, the green light emitting element. The ON time t _G-ON and OFF time t _{G-OFF of} 22G and the ON time t _B-ON and OFF time t _{B-OFF of} the blue light emitting element 22B are determined in the light emitting element driving circuit 94. still,
t _R-ON + t _R-OFF = t _G-ON + t _G-OFF = t _B-ON + t _B-OFF = constant value t _Const
It is. The duty ratio in driving based on pulse width modulation of the light emitting diode is
t _ON / (t _ON + t _OFF ) = t _ON / t _Const
Can be expressed as

The signals corresponding to the on times t _R-ON , t _G-ON , t _B-ON of the red light emitting element 22R, the green light emitting element 22G, and the blue light emitting element 22B constituting the planar light source unit 21 are driven by the light emitting element. The control switches 97R, 97G, and 97B are turned on by the light emitting element drive circuit 94 based on the signal values corresponding to the on times t _R-ON , t _G-ON , and t _B-ON. Only t _R-ON , t _G-ON , and t _B-ON are turned on, and the LED driving current (forward current) from the light emitting element driving power supplies 96R, 96G, 96B flows to each light emitting element 22R, 22G, 22B. It is. As a result, each of the light emitting elements 22R, 22G, and 22B emits light for the on times t _R-ON , t _G-ON , and t _B-ON in one image display frame. Thus, each display area unit 12 is illuminated at a predetermined illuminance.

The states thus obtained are indicated by solid lines in FIGS. 8A and 8B, and FIG. 8A shows an input signal input to the liquid crystal display device driving circuit 85 to drive the sub-pixels. 9 is a diagram schematically showing a relationship between a value obtained by raising the value of x to the power of 2 (x′≡x ^2.2 ) and a duty ratio (= t _ON / t _Const ). FIG. It is a figure which shows typically the relationship between the value X of the control signal for controlling the light transmittance Lt, and the display brightness | luminance y.

[Step-150]
On the other hand, the values x _R , x _G , x _B of the input signals [R, G, B] input to the liquid crystal display device driving circuit 85 are sent to the timing controller 86, and are input to the timing controller 86. A control signal [R, G, B] corresponding to the input signal [R, G, B] is supplied (output) to the sub-pixel [R, G, B]. The values X _R and X _{G of the} control signal [R, G, B] generated by the timing controller 86 of the liquid crystal display device driving circuit 85 and supplied from the liquid crystal display device driving circuit 85 to the sub-pixels [R, G, B]. , X _B and the values x _R , x _G , x _{B of} the input signals [R, G, B] are expressed by the following equations (4-1), (4-2), and (4-3): There is a relationship. However, _{b1_R} , _{b0_R} , _{b1_G} , _{b0_G} , _{b1_B} , _{b0_B} are constants. Further, since the light source luminance Y ₂ of the planar light source unit 21 is changed for each image display frame, the control signal [R, G, B] basically sets the value of the input signal [R, G, B] to 2. A value obtained by performing correction (compensation) based on a change in the light source luminance Y _{2 with} respect to the squared value. That is, since the light source luminance Y ₂ for each image display frame is changed, the light source luminance Y ₂ (≦ Y ₁₎ control signal so that the display luminance · second specified value y ₂ obtained in [R, G, B] The values X _R , X _G , and X _B are determined and corrected (compensated) to control the light transmittance (aperture ratio) Lt of the pixel or sub-pixel. Here, the functions f _R , f _G , and f _B in the equations (4-1), (4-2), and (4-3) are functions obtained in advance for performing such correction (compensation). is there.

X _R = f _R (b 1 _—R · x _R ^2.2 + b 0 _—R ) (4-1)
X _G = f _G (b 1 _—G · x _G ^2.2 + b 0 _—G ) (4-2)
X _B = f _B (b 1 _—B · x _B ^2.2 + b 0 _—B ) (4-3)

  Thus, the image display operation in one image display frame is completed.

The second embodiment is a modification of the first embodiment. If the initial forward voltage value V _f-0 is measured in a state where the time to the left has not elapsed since the end of the operation of the surface light source device 20 and the light emitting element 22 is not sufficiently cooled, due to residual heat. If the light emitting element 22 is somewhat higher than the ambient temperature, the accurate initial forward voltage value V _f-0 may not be measured.

In the second embodiment, the planar light source device 20 further includes a timer 92. Then, the time from the end of the operation of the surface light source device 20 to the next start-up is measured by the timer 92, and when the measured time is equal to or less than a predetermined time (for example, 1 hour or less), the surface light source device 20 In the next start-up, the driving condition of the light emitting element 22 is determined based on the initial forward voltage value V _f-0 and the initial atmospheric temperature T ₀ which were obtained during the previous operation of the planar light source device 20. . Specifically, for example, a drive current for driving the light emitting element 22 is determined. Note that the initial forward voltage value V _f-0 and the initial ambient temperature T ₀ obtained in the previous reference measurement mode of the planar light source device 20 may be stored in the storage device 82.

Third Embodiment The third embodiment relates to a lighting device control method and a liquid crystal display device assembly driving method according to the second aspect of the present invention. The liquid crystal display device assembly of Example 3 is the same as the liquid crystal display device assembly of Example 1,
(A) a liquid crystal display device (more specifically, a transmissive color liquid crystal display device 10 having a display region composed of pixels arranged in a two-dimensional matrix), and
(B) a planar light source device 20 for illuminating the color liquid crystal display device 10 from the back surface;
It has.

And the planar light source device 20 of Example 3, or the illuminating device 20 of Example 3,
(A) Light-emitting element 22, and
(B) a light emitting element drive control circuit 90 for supplying current to the light emitting element 22 and measuring the light emission amount and forward voltage value of the light emitting element 22;
And further,
(C) temperature measuring means 70 for measuring the ambient temperature around the light emitting element 22;
It has. In the third embodiment, it is not essential to provide the temperature measuring means 70.

  Hereinafter, the control method of the illumination device or the driving method of the liquid crystal display device assembly of Example 31 will be described. In Example 3, the irreversible change in the light emission amount of the light emitting element 22 is compensated. Even in the third embodiment, as a method of controlling the luminance of the light emitting element 22 to be constant, a method of controlling the number of pulses when the light emitting element 22 is driven based on the PWM control method is employed.

In the control method of the illumination device or the driving method of the liquid crystal display device assembly according to the third embodiment, the calibration operation is first performed when the planar light source device 20 is started up, that is, in the reference measurement mode. That is, the light emitting element drive control circuit 90 measures the initial light emission amount P ₀ and the initial forward voltage value V _f-0 .

Specifically, as in the first embodiment, as shown in FIG. 1A, immediately after the planar light source device 20 is powered on, the reference pulse is emitted from the light emitting element prior to starting the illumination of the liquid crystal display device. 22 is applied. When the planar light source device 20 is started up, the light emitting element 22 is equal to the ambient temperature (initial ambient temperature T ₀ ). The time length of the reference pulse is set to such a length that the heat generation of the light emitting device can be ignored. Specifically, the reference pulse has an initial drive current value I ₀ of, for example, 200 mA, and the time length is, for example, 5 microseconds. By applying such a reference pulse, the temperature of the light emitting element 22 does not increase. Accordingly, the ambient temperature (initial ambient temperature T ₀ ) at this time can be regarded as the junction temperature T _j .

More specifically, as shown in FIG. 1A, the initial pulse generation circuit 91 and the light emitting element driving circuit 94 are connected by a switch 93. An initial pulse is generated in the initial pulse generation circuit 91, and the initial pulse is sent to the light emitting element driving circuit 94. Based on the initial pulse, the light emitting element drive circuit 94 determines the on time t _ON and the off time t _OFF of the light emitting element 22. A current flowing through the light emitting element 22 obtained by a combination of the on time t _ON and the off time t _OFF is a reference pulse. On the other hand, the light emitting element driving circuit 94 sends a signal to the light emitting element driving power source 96 to flow the initial driving current value I ₀ . From the light emitting element driving power source 96, an initial driving current value I ₀ (specifically, for example, 200 mA) for driving the light emitting element 22 is supplied. Then, under the control of the light emitting element driving circuit 94, the control switch 97 is turned on / off based on the on time t _ON and the off time t _OFF . The total sum of the on time t _ON and the off time t _OFF is, for example, 5 microseconds. Then, the value of the potential difference across the light emitting element 22 based on the initial drive current value I ₀ at this time is measured by the forward voltage measurement circuit 95 as the initial forward voltage value V _f-0 , and the initial forward voltage value V _f-0 is sent to the light emitting element driving circuit 94. At the same time, the ambient temperature (initial ambient temperature T ₀ ) at this time is measured by the temperature measuring means 70 for reference. The temperature measurement data is also sent to the light emitting element driving circuit 94. Further, the initial light emission amount P ₀ of the light emitting element 22 is measured by the light detecting means 71, and the light emission amount measurement data is also sent to the light emitting element driving circuit 94. The above operation is performed on the red light emitting element 22R, the green light emitting element 22G, and the blue light emitting element 22B, and the value of the coefficient “C” in each of the red light emitting element 22R, the green light emitting element 22G, and the blue light emitting element 22B is obtained. .

When the planar light source device 20 is operating (in the normal light emission mode), the forward voltage value V _f is measured by the light emitting element drive control circuit 90 as shown in FIG. ₀ , the driving condition of the light emitting element 22 is determined based on the initial forward voltage value V _f-0 and the forward voltage value V _f . Specifically, the drive current for driving the light emitting element 22 is determined. Then, the light emitting element 22 is driven with the determined drive current.

Specifically, at the start of the operation of the planar light source device 20, for example, the light emitting element 22 is driven by the initial drive current value I ₀ at the same level as that at the time of calibration. The amount of light corresponding to the drive current value I ₀ is output. Then, when the operation of the planar light source device 20 is continued and the initial drive current value I ₀ continues to flow through the light emitting element 22, the temperature of the light emitting element 22 rises due to the heat generation of the light emitting element 22, and the junction temperature T _j Rises. As a result, the light emission characteristics of the light emitting element 22 vary. Specifically, in the light emitting element 22, the amount of light emission decreases, and the dominant wavelength changes to the long wavelength side. Therefore, the value of the potential difference across the light emitting element 22 based on the initial drive current value I ₀ is measured in the forward voltage measurement circuit 95 as a forward voltage V _f, the forward voltage V _f emitting element driving circuit 94 Is sent out. In addition, the ambient temperature T at this time is measured by the temperature measuring means 70 for reference, and the temperature measurement data is sent to the light emitting element driving circuit 94. Thus, in the light emitting element driving circuit 94, the value of the formula (G), that is,
P (T _j ) = P ₀ − (D / B) (V _f −V _f−0 ) (G)
(B and D are constants obtained in advance), and the drive current is determined based on the obtained values. Specifically, in the light emitting element driving circuit 94, the value of the light emission amount P (T _j ) depending on the junction temperature T _j can be obtained based on the equation (G). Based on the value of the junction temperature T _j, the light emission amount and the dominant wavelength are obtained in advance so as to obtain the same light emission amount and dominant wavelength as when the initial drive current value I ₀ was passed through the light emitting element 22 at the start of the operation of the planar light source device 20. In order to drive the light emitting element 22 based on the relationship between the junction temperature T _j , the forward voltage value V _f , the light emitting element driving current, and the amount of light emission (the relation is stored in the storage device 82). , And the light emitting element 22 is driven with the determined drive current. The difference between the ambient temperature T and the junction temperature T _j is determined by the product of the thermal resistance value of the light emitting element 22 and the amount of heat generated. Therefore, by measuring the normal thermal resistance value in advance and storing it in the storage device 82, for example, by measuring the atmospheric temperature T, it is possible to detect an abnormality.

More specifically, as shown in FIG. 1B, a pulse width modulation output signal (described later) is sent from the planar light source device control circuit 80 to the light emitting element driving circuit 94 via the switch 93. In the light emitting element driving circuit 94, the on time t _ON and the off time t _{OFF of} the light emitting element 22 are determined based on the pulse width modulation output signal. A driving current for driving the light emitting element 22 is added to the on time t _ON and the off time t _OFF . Specifically, the on-time t _ON and the off-time t _OFF are increased based on the determined drive current (more specifically, the integrated value of the drive current) to be passed through the light emitting element 22 described above. Namely, the total value of the on-time t _ON based on the pulse width modulated output signal as a Total _ON, the total value of the on-time t _ON which determined drive current is taken into account for driving the light emitting element 22 and Total _ON ' Then
P (T _j ) × Total _ON '= P ₀ × Total _ON
There is a relationship. The value of current supplied from the light emitting element driving power supply 96 for driving the light emitting element 22 is an initial driving current value I ₀ . Then, under the control of the light emitting element driving circuit 94, the control switch 97 is turned on / off based on the on time t _ON and the off time t _OFF (Total _ON '), and the light emitting element 22 emits light. The control of Total _ON ′ may be performed for each image display frame, or may be performed for each predetermined number of image display frames. This state is as shown in FIG. By increasing the duty ratio as the junction temperature T _j increases, the luminance of the light emitting element 22 can be controlled to be constant.

The fourth embodiment is a modification of the third embodiment. The initial light emission amount P ₀ and the initial forward voltage value V _f-0 are measured in a state where the time to the left has not elapsed since the operation of the planar light source device 20 has not elapsed and the light emitting element 22 is not sufficiently cooled. Therefore, when the light emitting element 22 is somewhat higher than the ambient temperature due to the residual heat, the accurate initial light emission amount P ₀ and the initial forward voltage value V _f-0 may not be measured.

In the fourth embodiment, the planar light source device 20 further includes a timer 92. Then, the time from the end of the operation of the surface light source device 20 to the next start-up is measured by the timer 92, and when the measured time is equal to or less than a predetermined time (for example, 1 hour or less), the surface light source device 20 In the next start-up, the driving condition of the light emitting element 22 is determined based on the initial light emission amount P ₀ and the initial forward voltage value V _f-0 obtained during the previous operation of the planar light source device 20. . Specifically, for example, a drive current for driving the light emitting element 22 is determined. Note that the initial light emission amount P ₀ and the initial forward voltage value V _f-0 obtained in the previous reference measurement mode of the planar light source device 20 and the initial ambient temperature T ₀ are stored in the storage device 82. You just have to.

  Except for the above points, the control method of the lighting device and the driving method of the liquid crystal display device assembly of the fourth embodiment are the same as the control method of the lighting device and the driving method of the liquid crystal display device assembly of the third embodiment. Since it can, detailed explanation is omitted.

  As mentioned above, although this invention was demonstrated based on the preferable Example, this invention is not limited to these Examples. The configurations and structures of the transmissive color liquid crystal display device, the planar light source device, the planar light source unit, the liquid crystal display device assembly, various drive circuits, and temperature measuring means described in the embodiments are examples, and these are configured. The member, material, etc. to perform are also examples, and can be changed as appropriate. In the embodiments, the description has been made on the assumption that the display area of the liquid crystal display device is divided into P × Q virtual display area units. However, in some cases, the transmissive liquid crystal display device has P × Q. You may have the structure divided | segmented into the actual display area unit. Temperature control of the light emitting element 22 (cooling of the light emitting element 22 or the like) may be performed by monitoring the temperature of the light emitting diode with a temperature measuring unit and feeding back the result to the light emitting element drive control circuit. Furthermore, in Example 1 to Example 4, the white hue as the sum of the light emission amounts of the red light emitting element, the green light emitting element, and the blue light emitting element may be controlled.

The lighting device control method and the liquid crystal display device assembly driving method described in the first embodiment may be combined with the lighting device control method and the liquid crystal display device assembly driving method described in the third embodiment. . That is,
(A) Light emitting element 22,
(B) a light emitting element drive control circuit 90 for supplying current to the light emitting element 22 and measuring the light emission amount and forward voltage value of the light emitting element 22, and
(C) temperature measuring means 70 for measuring the ambient temperature around the light emitting element 22;
A control method of a lighting device (or a driving method of a liquid crystal display device assembly) comprising:
When the lighting device (planar light source device) is started up, the light emitting element drive control circuit 90 measures the initial forward voltage value V _f-0 and the initial light emission amount P ₀ , and at the same time, the temperature measuring means 70 performs the initial atmosphere. Measure the temperature T ₀
During operation of the illumination device (planar light source device), the forward voltage value _Vf is measured by the light emitting element drive control circuit 90, and the initial forward voltage value _Vf-0 , the forward voltage value _Vf , and the initial light emission amount. A method of determining the driving condition of the light emitting element 22 based on the values of P ₀ and the initial ambient temperature T ₀ may be adopted. Moreover, you may combine the control method of the illuminating device demonstrated in Example 2 or Example 4, and the drive method of a liquid crystal display device assembly in the method concerned.

FIGS. 1A and 1B are conceptual diagrams for explaining the illumination device or the planar light source device according to the first embodiment. FIG. 2 is a conceptual diagram of a liquid crystal display device assembly including a color liquid crystal display device, a planar light source device, a liquid crystal display device drive circuit, and a light emitting element drive control circuit suitable for use in the first embodiment. FIG. 3 is a conceptual diagram of a light-emitting element drive control circuit according to the first embodiment. FIG. 4 is a schematic partial cross-sectional view of the planar light source device and the color liquid crystal display device according to the first embodiment. FIG. 5 is a schematic partial cross-sectional view of the color liquid crystal display device according to the first embodiment. FIG. 6 is a graph schematically showing temporal changes in the forward voltage value and the like for explaining the illumination device or the planar light source device according to the first embodiment. FIG. 7 is a flowchart for explaining a driving method of the liquid crystal display device assembly of the first embodiment. FIG. 8A shows a value (x′≡x ^2.2 ) obtained by multiplying the value of the control signal input to the light emitting element drive control circuit to drive the subpixel by the power of 2.2 (x′≡x ^2.2 ) and the duty ratio (= t _ON / t _Const ) schematically shows the relationship between the control signal value X and the display luminance y for controlling the light transmittance of the sub-pixel. FIG. 9A and 9B are diagrams for explaining the relationship among the light source luminance of the planar light source device, the light transmittance (aperture ratio) of the pixel, and the display luminance in the display area in the first embodiment. It is a conceptual diagram. FIGS. 10A and 10B are graphs showing the ambient temperature dependence of the emission intensity of the blue light emitting diode and the green light emitting diode made of InGaN light emitting diodes, respectively. FIG. 11 is a graph showing the ambient temperature dependence of the emission intensity of a red light emitting diode made of an AlGaInP-based light emitting diode. FIG. 12 is a graph showing the ambient temperature dependence of the light emission amount and the dominant wavelength of the blue light emitting diode. 13A and 13B are diagrams for explaining the relationship among the light source luminance of the planar light source device, the light transmittance (aperture ratio) of the pixel, and the display luminance in the display area in the conventional technique. It is a conceptual diagram. FIGS. 14A and 14B show the temporal variation of the forward voltage value V _f of the light-emitting diodes aged with a constant current. Specifically, FIG. shows the relationship between the direction voltage V _f (relative value), the relationship between the storage time and the forward voltage V _f relative value when stored at 85 ° C environment (B) of FIG. 14 Show. FIG. 15 is a graph showing the relationship between storage time and light emission amount (relative value) when stored in an environment of 85 ° C. FIG. 16A is a graph in which the relationship between the forward current value _If and the forward voltage value _Vf is measured, and FIG. 16B shows the junction temperature _Tj and the forward voltage value _Vf. It is the graph which measured the relationship with.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Color liquid crystal display device, 11 ... Display area, 12 ... Display area unit, 20 ... Planar light source device (illumination device), 21 ... Planar light source unit, 22, 22R, 22G, 22B ... light emitting diode, 23 ... partition, 31 ... housing, 32A ... bottom of housing, 32B ... side of housing, 33 ... outer frame, 34 ... Inner frame, 35A, 35B ... spacer, 36 ... guide member, 37 ... bracket member, 41 ... light diffusion plate, 42 ... light diffusion sheet, 43 ... prism sheet, 44 ... Polarization conversion sheet, 45 ... Reflection sheet, 50 ... Front panel, 51 ... First substrate, 52 ... Color filter, 53 ... Overcoat layer, 54 ... Transparent first electrode (common electrode), 55 Alignment film, 56 ... polarizing plate (polarizing film / polarizing sheet), 60 ... rear panel, 61 ... second substrate, 62 ... switching element, 64 ... transparent second electrode, 65 ... Alignment film, 66, 66 '... Polarizing plate (polarizing film / polarizing sheet), 67 ... Insulating layer, 70 ... Temperature measuring means, 71, 71R, 71G, 71B ... Light Detection means, 80 ... planar light source device control circuit, 81 ... arithmetic circuit, 82 ... storage device (memory), 85 ... liquid crystal display device drive circuit, 86 ... timing controller, 90 ..Light emitting element drive control circuit, 91... Initial pulse generation circuit, 92... Timer, 93... Switch, 94. 96R, 96G, 96B ... Light emitting device driver Power (constant current source), 97,97R, 97G, 97B ··· control switch, 98,98R, 98G, 98B ··· resistor

Claims (12)

(A) a light emitting element,
(B) a light emitting element drive control circuit for supplying a current to the light emitting element and measuring a forward voltage value of the light emitting element;
(C) a temperature measuring means for measuring the ambient temperature around the light emitting element;
A control method for a lighting device comprising:
At the start of the lighting device, the initial forward voltage value V _f-0 is measured by the light emitting element drive control circuit, and the initial ambient temperature T ₀ is measured by the temperature measuring means.
During the operation of the lighting device, the forward voltage value V _f is measured by the light emitting element drive control circuit, and based on the initial forward voltage value V _f-0 , the forward voltage value V _f and the initial ambient temperature T ₀ , A method for controlling a lighting device, comprising: determining a driving condition of a light emitting element. A timer,
If the time from the end of operation of the lighting device to the next start-up is measured with a timer and the measured time is less than or equal to the predetermined time, the next start-up of the lighting device will be performed during the previous operation of the lighting device. The lighting device control method according to claim 1, wherein the driving condition of the light emitting element is determined based on the initial forward voltage value V _f−0 and the initial ambient temperature T _{0 obtained} in step 1. During the operation of the lighting device, the light emitting element drive control circuit generates a drive current for driving the light emitting element based on the initial forward voltage value V _f-0 , the forward voltage value V _f and the initial ambient temperature T _0. The method of controlling a lighting device according to claim 1, wherein the light emitting element is driven by the determined drive current. In the light emitting element drive control circuit, a value of T ₀ − (V _f −V _f−0 ) / B (where B is a constant) is obtained, and the drive current is determined based on the obtained value. The control method of the illuminating device of Claim 3.   The illuminating device control method according to claim 1, wherein the transmissive liquid crystal display device is illuminated from the back by the illuminating device. (A) a light emitting element, and
(B) a light emitting element drive control circuit for supplying a current to the light emitting element and measuring the light emission amount and the forward voltage value of the light emitting element;
A control method for a lighting device comprising:
When the lighting device is started up, the light emission element drive control circuit measures the initial light emission amount P ₀ and the initial forward voltage value V _f-0 ,
During operation of the lighting device, the forward voltage value V _f is measured by the light emitting element drive control circuit, and the light emitting element is based on the initial light emission amount P ₀ , the initial forward voltage value V _f-0 and the forward voltage value V _f. A control method for an illuminating device, wherein the driving condition is determined. A timer,
If the time from the end of operation of the lighting device to the next start-up is measured with a timer and the measured time is less than or equal to the predetermined time, the next start-up of the lighting device will be performed during the previous operation of the lighting device. The lighting device control method according to claim 6, wherein a driving condition of the light emitting element is determined based on the initial light emission amount P ₀ and the initial forward voltage value V _{f−0 obtained} in the step. During the operation of the lighting device, the light emitting element drive control circuit determines a driving current for driving the light emitting element based on the initial light emission amount P ₀ , the initial forward voltage value V _f-0 and the forward voltage value V _f. The method of controlling a lighting device according to claim 6, wherein the light emitting element is driven with the determined driving current. In the light emitting element drive control circuit, a value of P ₀ − (V _f −V _f−0 ) × (D / B) (where B and D are constants) is obtained, and the drive current is determined based on the obtained values. The method for controlling the lighting device according to claim 8.   The illuminating device control method according to claim 6, wherein the transmissive liquid crystal display device is illuminated from the back by the illuminating device. (A) a liquid crystal display device, and
(B) a planar light source device for illuminating the liquid crystal display device from the back surface;
A method of driving a liquid crystal display device assembly comprising:
The planar light source device
(A) a light emitting element,
(B) a light emitting element drive control circuit for supplying a current to the light emitting element and measuring a forward voltage value of the light emitting element;
(C) a temperature measuring means for measuring the ambient temperature around the light emitting element;
It has
At the time of starting the surface light source device, the initial forward voltage value V _f-0 is measured by the light emitting element drive control circuit, and the initial ambient temperature T ₀ is measured by the temperature measuring means.
During the operation of the planar light source device, the forward voltage value V _f is measured by the light emitting element drive control circuit, and the initial forward voltage value V _f-0 , the forward voltage value V _f and the initial ambient temperature T ₀ are set. A driving method for a liquid crystal display device assembly, wherein a driving condition for a light emitting element is determined based on the driving condition. (A) a liquid crystal display device, and
(B) a planar light source device for illuminating the liquid crystal display device from the back surface;
A method of driving a liquid crystal display device assembly comprising:
The planar light source device
(A) a light emitting element, and
(B) a light emitting element drive control circuit for supplying a current to the light emitting element and measuring the light emission amount and the forward voltage value of the light emitting element;
It has
When starting the planar light source device, the light emission element drive control circuit measures the initial light emission amount P ₀ and the initial forward voltage value V _f-0 ,
During operation of the planar light source device, the forward voltage value V _f is measured by the light emitting element drive control circuit, and based on the initial light emission amount P ₀ , the initial forward voltage value V _f-0 and the forward voltage value V _f , A driving method of a liquid crystal display device assembly, wherein driving conditions of a light emitting element are determined.

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