JPH08304827A - Lighting device for liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide a lighting device for a liquid crystal display device turning off only a relevant tube or a block containing the tube and turning off no all tubes when one tube among plural light source tubes constituting the lighting device is dead. CONSTITUTION: This device is provided with plural lighting circuits 10 provided with a life detection circuit 12 for detecting the life of a hot cathode tube 13 and a turn-off circuit 11 turning off the hot cathode tube 13 according to the output of the life detection circuit 12. Then, by independently controlling at least one answering hot cathode tube 13 with these lighting circuits 10, when the matter that answering one hot cathode tube 13 runs out is detected by the life detection circuit 12, the supply of a turn-on voltage to the hot cathode tube 13 is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device for a liquid crystal display device using a plurality of hot cathode tubes.

[0002]

2. Description of the Related Art A liquid crystal display device has a display panel in which a nematic liquid crystal or a smectic liquid crystal is interposed between a pair of substrates. In particular, a chiral smectic liquid crystal or a chiral nematic liquid crystal is used, and if a pixel can maintain a display state (alignment state of liquid crystal molecules) for at least one frame scanning period, a large-screen display panel with a diagonal of 15 inches or more can be obtained. It can be created relatively easily.

With the increase in screen size, it has become necessary to use a plurality of lamps, which are light sources, in an illumination device called a backlight. Therefore, the present inventors have manufactured a lighting device for a liquid crystal display device using a hot cathode tube. By the way, when an illumination device is manufactured using a hot cathode tube in this way, the hot cathode tube causes filament breakage at the end of its life, causing abnormal heat generation in the vicinity of the electrode at the end of the tube, causing deformation of other components. Come and go

Therefore, a safety measure at the end of the life of the tube is indispensable. As a safety measure at the end of the life of the tube, an increase in the lighting voltage of the tube at the end of the life is detected, and a temperature fuse or thermistor is arranged near the electrode of the tube. Then, I tried to provide a life detecting means such as detecting the temperature at the time of abnormal heat generation. Then, when the life is detected, the operation of the inverter is stopped to turn off all the tubes of the lighting device.

[0005]

However, in the above-described life detection control in the conventional hot cathode tube lighting device, the operation of the inverter stops when one of the tubes forming the lighting device reaches the end of its life. By turning off all the tubes, the liquid crystal display device equipped with this lighting device,
When the user used the display, the display screen suddenly went black and it became impossible to continue working.

According to the present invention, when one of the plurality of light source tubes constituting the illuminating device has reached the end of its life, only the corresponding tube or a block including the tube is turned off and all the lamps are turned off. It is an object of the present invention to provide a lighting device for a liquid crystal display device that does not have such a problem.

[0007]

Means for Solving the Problems The present invention which achieves the above-mentioned object is an illumination device used in a liquid crystal display device having a liquid crystal display panel and an illumination means provided on the back side of the liquid crystal display panel, At least one hot cathode tube, and a life detection circuit for detecting the life of the hot cathode tube;
A plurality of lighting circuits each having an extinguishing circuit for extinguishing the hot cathode tube according to the output of the life detecting circuit, each lighting circuit independently controlling the corresponding at least one hot cathode tube; Is a lighting device for a liquid crystal display device.

Each illumination circuit may detect the life of one corresponding hot cathode tube and stop the supply of the lighting voltage to the corresponding one hot cathode tube.

On the other hand, if each lighting circuit detects the life of at least one of the corresponding hot cathode tubes and stops the supply of the lighting voltage to the corresponding hot cathode tubes, It is preferable because the system becomes more compact.

As the life detecting circuit, if a voltage detecting circuit for detecting and detecting the lighting voltage of the hot cathode tube and a comparing circuit for comparing the output voltage of the voltage detecting circuit with a reference voltage are used, the life is a simple circuit. Can be detected.

On the other hand, as the life detecting circuit, a temperature sensor for detecting the temperature of the hot cathode tube, a voltage conversion circuit for converting the output of the temperature sensor into a voltage, and an output voltage from the voltage conversion circuit are used as reference voltages. You may use the comparison circuit which compares with.

The device can be made thin by using, as the hot cathode tube, one arranged at the end of the light guide plate arranged on the back surface side of the liquid crystal display panel.

On the other hand, a plurality of the hot cathode tubes may be arranged in parallel on the back surface side of the liquid crystal display panel with a space therebetween.

When there is no change in the image displayed on the liquid crystal display panel even after a lapse of a predetermined time, a signal for turning off the hot cathode tubes is supplied to all the illumination circuits to further extend the life. You can

As the liquid crystal display panel, a ferroelectric liquid crystal element or an antiferroelectric liquid crystal element having a chiral smectic liquid crystal between the substrates, which is easy to have a large screen, is desirable.

An element having a chiral nematic liquid crystal exhibiting two metastable molecular alignment states between a pair of substrates may be used as the liquid crystal display panel.

At least one pair of symmetrically arranged hot cathode tubes may be turned off.

According to the present invention, when any one of the hot cathode tubes in the illuminating device reaches the end of its life, only that tube or a block including the tube is turned off, so that all the lamps are turned off and it becomes completely dark. In the case of the display device, it is possible to continue the display work without any trouble.

[0019]

1 is a diagram showing the configuration of a lighting device for a liquid crystal display device according to a first embodiment of the present invention.

In the figure, a plurality of 13, 13 in the present embodiment, two light sources are lit and controlled by two independent lighting circuits 10. Here, the illumination circuit 10 includes a life detection circuit 12 that detects the life of the light source 13, and a light-off circuit 11 that turns off the light source 13 according to the output signal of the life detection circuit 12. And
Each of these lighting circuits 10 is adapted to turn on the light source 13 using the power supply voltage supplied from the common power supply 117.

Both of the two light sources 13 are arranged on the rear surface BSC side of the liquid crystal display panel LCP so that the user can recognize the display image from the front surface FSC side of the panel LCP.

Incidentally, the lighting circuit 1 used in the present invention.
The zero life detecting circuit 12 is configured as shown in FIG. 2 (A) or (B).

In FIG. 2A, the lighting voltage applied to the hot cathode tube 13 as a light source is detected by the voltage detection circuit 12b, and the detection signal voltage and the reference voltage are compared with each other by the voltage comparison circuit 12.
When a is compared and the detection signal voltage becomes higher than the reference voltage indicating the life, the voltage comparison circuit 12a outputs a high level signal or a low level signal. Then, the extinguishing circuit 11 receiving this output stops the voltage supply to the hot cathode tube 13 and the hot cathode tube 13 is extinguished. As the voltage detection circuit 12b, for example, a detection circuit in which a rectifying element such as a diode and a low pass filter such as a capacitor are appropriately combined is used.

On the other hand, the life detecting circuit 12 is shown in FIG.
As shown in, a temperature sensor 12d for detecting the temperature of the hot cathode tube 13 and a voltage conversion circuit 12c may be used instead of the voltage detection circuit 12b. Here, the temperature sensor 12d includes, for example, a thermistor whose resistance value changes depending on the temperature, and the voltage conversion circuit 12c causes a voltage drop depending on the temperature by supplying a current to the thermistor. It is a circuit to make.

Then, the voltage thus obtained is compared with the reference voltage in the voltage comparison circuit 12a, and when the detection signal voltage becomes higher than the reference voltage indicating the life, the voltage comparison circuit 12a.
Outputs a high level or low level signal. Here, the configuration of the voltage comparison circuit 12a is the same as in the case of (A). The configuration (B) is effective when the life of the light source and the amount of heat generated by the light source are correlated.

By the way, the liquid crystal display panel LCP used in the present invention has a liquid crystal LC disposed between a pair of translucent substrates SB such as glass, quartz and plastic.

As the liquid crystal LC used in the liquid crystal display panel LCP, a chiral smectic liquid crystal exhibiting a chiral smectic phase or a chiral nematic liquid crystal exhibiting a chiral nematic phase is suitable. The former is known as a ferroelectric liquid crystal element or an antiferroelectric liquid crystal element, and the latter is known as a bistable twisted nematic (BTN) liquid crystal element. The display state can be retained.

Further, a hot cathode tube is preferably used as the light source of the present invention. As the hot cathode tube, red,
It is possible to use a fluorescent lamp that emits white light having broad spectral characteristics in a wide wavelength range of green and blue. More preferably, it is preferable to use a three-wavelength fluorescent lamp that emits white light having emission peaks with narrow half widths in the three wavelength regions of red, green, and blue.

On the other hand, the arrangement of the hot cathode tubes is an edge light type in which four or two in total are arranged on four sides or two opposite sides of a rectangular acrylic light guide plate, or a plurality of hot cathode tubes are arranged on the surface of a display panel. It may be either a direct type arranged in parallel.
FIG. 3 is a diagram showing a schematic configuration of an illumination device for a liquid crystal display device according to a second embodiment of the present invention in which four hot cathode tubes are arranged.

In the figure, 101 to 104 are hot cathode tubes which are four light sources, 113 to 116 are hot cathode tube life detecting circuits, 109 to 112 are lighting stop circuits for the tubes 101 to 104, and 105 to 108 are. The four lighting circuits are lighting circuits, and these four lighting circuits are the hot cathode tubes 101 to 104 and the life detection circuit 11
3 to 116, lighting stop circuits 109 to 112, lighting circuit 1
It consists of 05-108 and the power supply 117.

Here, the life detecting circuits 113 to 116 are for constantly monitoring the lighting voltages of the respective tubes 101 to 104. Then, the life detection circuits 113 to 1
When the hot cathode tubes 101 to 104 approach the end of their life and the lighting voltage of the tubes 101 to 104 gradually rises and exceeds a predetermined voltage, 16 is regarded as the life of the tubes 101 to 104, and the lighting stop circuits 109 to 112. A life detection signal is sent to.

Further, the lighting stop circuits 109 to 112 stop the lighting operation of the lighting circuits 105 to 108 based on the life detection signal. By stopping the lighting operation of the tubes 101 to 104 in this manner, it becomes possible to avoid the filament breakage at the end of the life of the hot cathode tubes 101 to 104 and the abnormal heat generation at the tube ends. There is.

For example, when the first life detecting circuit 113 determines that the first hot cathode tube 101 has reached the end of life, a life detecting signal is sent to the first lighting stop circuit 109, whereby
The lighting circuit 105 stops the lighting operation, and the first hot cathode tube 10
1 is turned off. As a means for detecting the life, specifically, the voltage across the tube is stepped down and rectified by resistance division and input to a comparator such as a comparator IC, a predetermined threshold value is set, and the tube is operated until it exceeds that value. The tube is turned on, and when the value exceeds that value, it is determined that the tube is at the end of its life, and the lighting operation is stopped.

In this embodiment, the life detecting circuits 113 to 116 are arranged in each of the plurality of hot cathode tubes 101 to 104 constituting the illuminating device 10, and the respective tubes 101 to 104 are independently controlled to be turned on. Lighting circuit 105-
108, the voltage across the tubes is constantly monitored during the lighting operation of the tubes 101 to 104.

In this case, the tubes 101 to 101 constituting the lighting device.
By independently providing the lighting circuits 105 to 108 by the number of 104, only the tubes 101 to 104 at the end of life are turned off.
The other normal tubes 101-104 remain lit. As a result, it is possible for the user of this liquid crystal display device to avoid the problem that the screen suddenly goes black and the work becomes impossible. However, in the case of an illuminating device having more than two lamps, a circuit for stopping the lighting operation is required for each tube, which results in a high cost as a product. Therefore, when extinguishing the tubes, it is possible to reduce the cost by extinguishing the two tubes as a set, rather than extinguishing them one by one.

FIG. 4 is a diagram showing a schematic configuration of an illumination device for a liquid crystal display device according to the third embodiment of the present invention thus configured. In the figure, reference numerals 211 to 214 denote life detecting circuits, and the life detecting circuits 211 to 214
Is arranged for each hot cathode tube 201-204, and the two lighting circuits 205, 206 are not for each tube but for the first and second lighting circuits 205, 206.
Hot cathode tubes 201, 202 and third and fourth hot cathode tubes 20
It is designed such that 3,204 are made into one block and two blocks are lit each. 207 to 210 are lighting stop circuits that stop the lighting operation of the tube when the life detection signals from the life detection circuits 211 to 214 are received.

In this structure, for example, the first hot cathode tube 2
When 01 is determined to be the life, a life detection signal is transmitted from the life detection circuit 211, the first lighting stop circuit 207 that receives the signal operates to stop the first lighting circuit 205, and the first and second heat The cathode tubes 201 and 202 are turned off at the same time. At this time, since the first lighting stop circuit 207 is independent of the second lighting circuit 206, the third and fourth hot cathode tubes 203 and 204 are continuously lit as they are.

As described above, the lighting control according to this configuration does not turn off all the lights even when one of the tubes forming the lighting device reaches the end of its life, which is simpler than the above-described second embodiment. The effect can be realized with a simple circuit configuration, that is, at low cost.

By the way, FIG. 5 shows an edge light type in which the light sources shown in FIG. 4 are arranged in two lamps on two sides, 301, 302, 303 and 304 are hot cathode tubes, and 305 is a hot cathode tube. The light guide is shown. In the figure, the reflectors of the hot cathode tubes 301, 302, 303, 304, the reflection plate on the back surface of the light guide, and the diffusion sheets on the upper surface of the light guide are omitted.

Then, in this way, the hot cathode tubes 301, 30
When 2, 303, 304 are arranged, the life detection control is performed with the first and third hot cathode tubes 301, 303 and the second and fourth hot cathode tubes 302, 304 symmetrically arranged as a set (block). To Thereby, for example, when the first hot cathode tube 301 reaches the end of its life, the third hot cathode tube 303 is arranged symmetrically with the first hot cathode tube 301 and forms a pair.
Only two of the tubes are turned off, and the remaining two tubes 302 and 304 are continuously turned on.

As a result, the number of lighting circuits can be reduced from four to two, and the cost can be reduced.

The combination of the tubes is arbitrary, but when the two tubes are turned on after the two tubes are extinguished, the combination of the present embodiment is taken to obtain the lighting device. 1 without any significant loss of brightness distribution
The effect is that the user of the display device does not feel uncomfortable even after the tube of the book is turned off at the end of its life.

FIG. 6 shows an edge light type in which light sources are provided on four sides.
As to how to turn off the light guide type lighting device, the first and third hot cathode tubes 401 and 40 are arranged symmetrically to each other.
By treating the third and second and fourth hot cathode tubes 402 and 404 as a pair, the first and second hot cathode tubes 401 and 40
The effect is that the luminance distribution when the two lamps are off is better than the combination of the second, third, and fourth hot cathode tubes 403 and 404. 405 is a light guide such as an acrylic plate.

On the other hand, FIG. 7 shows a direct type in which four light sources are arranged on the back surface of the display panel. In such a direct type 4 lamp, the first and fourth hot cathode tubes 50 are arranged symmetrically.
1,504 and the second and third hot cathode tubes 502,503 or the first and third hot cathode tubes 501,503 and the second and fourth hot cathode tubes 502,504 are combined and turned off. For the first and fourth hot cathode tubes 5
01, 504 and second and third hot cathode tubes 502, 503 or first and third hot cathode tubes 501, 503 and second and fourth
By combining the hot cathode tubes 502 and 504, the same effect as described above can be obtained.

Reference numeral 505 denotes a reflection frame of the lighting device, and other members such as a diffuser plate are not shown. Then, the extinction control of the hot cathode tubes arranged in the edge light type or the direct type as shown in FIGS. 5 to 7 can be performed by the control method of FIG. 3 or 4. Further, the same effect can be obtained by appropriately combining the lighting devices including six and eight lighting devices with the same idea.

Further, as a means for detecting the life of the tube, as described above, a temperature detecting element such as a thermistor may be used in addition to the means for monitoring the lighting voltage of the tube. When a temperature sensing element is used, the temperature at the end of the pipe at the end of its life is monitored for rise, and if it rises above a certain temperature,
The operation of the lighting circuit may be stopped similarly to the tube voltage detection method, and the control method for extinguishing the tube is also the same.

On the other hand, FIG. 8 shows three hot cathode tubes 13, 13.
It is a direct type device using a, and when the hot cathode tube 13a in the middle of FIG. 8 has reached the end of life, only this hot cathode tube 13a is turned off, and either of the hot cathode tubes 13 at both ends has reached the end of life. In the case of, the hot cathode tubes 13 at both ends are turned off.

Further, FIG. 9 shows an edge light type device using eight hot cathode tubes 13, and two hot cathode tubes 13 symmetrically arranged with respect to each other are turned on or off.

Here, in the liquid crystal display device in which the above-mentioned illumination devices are arranged on the back surface of the liquid crystal display element, it is not necessary to care when the illumination on the display surface is turned off, and even when the illumination is turned off, all lights are turned off. Not, so you'll be able to continue working.

Further, the power supply of each lighting device is controlled to be turned on and off, and when the display image is not changed for a certain period of time, the power supply from the power supply to the lighting circuit is stopped and all the light sources are turned on. It is desirable to turn off the lights. Then, with such a configuration, power consumption can be reduced.

Whether or not the display image is changed is as follows.
This can be determined by monitoring the rewriting of the VRAM that stores the display image data. That is, when the VRAM data is rewritten by mouse input or keyboard input, the life detection circuit operates again to turn on the light sources of blocks other than the block including the light source that has reached the end of its life.

The present invention can be implemented in various other forms without departing from the spirit or the main features thereof. Therefore, the above embodiments are merely examples in all respects, and should not be limitedly interpreted.
The scope of the present invention is defined by the claims and is not bound by the text of the specification. Further, all modifications and changes belonging to the equivalent range of the claims are within the scope of the present invention.

[0053]

As described above, according to the present invention,
In a lighting device using a plurality of hot cathode tubes of a liquid crystal display device, when detecting the life of the tubes and stopping the operation of the lighting circuit,
Since it is not possible to turn off all the lights of the hot cathode tubes that make up the lighting device at a time, it is possible to avoid the problem that the screen display suddenly disappears at all while the operator of the display device is working. .

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a lighting device for a liquid crystal display device according to a first embodiment.

FIG. 2 is a diagram showing a life detection circuit of a lighting device for a liquid crystal display device according to the embodiment.

FIG. 3 is a schematic configuration diagram of a lighting device for a liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of an illumination device for a liquid crystal display device according to a third embodiment of the present invention.

FIG. 5 is a perspective view of an example of an edge light type lighting device.

FIG. 6 is a perspective view of another example of the edge light type lighting device.

FIG. 7 is a perspective view of an example of a direct type illumination device.

FIG. 8 is a diagram showing an example of an arrangement of light sources used in the present invention and a control circuit thereof.

FIG. 9 is a diagram showing another example of the arrangement of light sources and the control circuit thereof used in the present invention.

[Explanation of symbols]

13, 13a, 101-104, 201-204, 30
1 to 304, 401 to 404, 501 to 504 hot cathode tube 10 lighting circuit 11 extinguishing circuit 12, 211 to 214 life detection circuit 117 power supply

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H05B 41/24 H05B 41/24 G

Claims (15)

[Claims] 1. A lighting device used for a liquid crystal display device having a liquid crystal display panel and a lighting means provided on the back side of the liquid crystal display panel, wherein at least one hot cathode tube and the life of the hot cathode tube are provided. Is provided with a plurality of lighting circuits each having a life detection circuit for detecting, and a turn-off circuit for turning off the hot cathode tube according to the output of the life detection circuit. Each lighting circuit corresponds to the at least one An illumination device for a liquid crystal display device, which independently controls the hot cathode tube. 2. The liquid crystal according to claim 1, wherein each lighting circuit detects the life of one corresponding hot cathode tube and stops the supply of the lighting voltage to the corresponding one hot cathode tube. Lighting device for display device. 3. Each illumination circuit detects the life of at least one of the corresponding hot cathode tubes and stops the supply of the lighting voltage to the corresponding hot cathode tubes. Item 2. An illumination device for a liquid crystal display device according to item 1. 4. The life detection circuit includes a voltage detection circuit for detecting and detecting a lighting voltage of the hot cathode tube, and a comparison circuit for comparing an output voltage of the voltage detection circuit with a reference voltage. The lighting device for a liquid crystal display device according to claim 1. 5. The life detecting circuit includes a temperature sensor for detecting the temperature of the hot cathode tube, a voltage converting circuit for converting an output of the temperature sensor into a voltage, and an output voltage from the voltage converting circuit as a reference voltage. The illumination device for a liquid crystal display device according to claim 1, further comprising a comparison circuit for comparison. 6. The illumination device for a liquid crystal display device according to claim 1, wherein the hot cathode tube is arranged at an end portion of a light guide plate arranged on a back surface side of the liquid crystal display panel. 7. The lighting device for a liquid crystal display device according to claim 1, wherein a plurality of the hot cathode tubes are arranged in parallel with each other on the back surface side of the liquid crystal display panel with an interval therebetween. 8. The liquid crystal display device according to claim 1, wherein all the hot cathode tubes are turned off when there is no change in the image displayed on the liquid crystal display panel even after a lapse of a predetermined time. Lighting equipment. 9. A signal for turning off the hot cathode tubes is supplied to all the illumination circuits when there is no change in the image displayed on the liquid crystal display panel even after a lapse of a predetermined time. An illumination device for a liquid crystal display device according to claim 1. 10. The lighting device for a liquid crystal display device according to claim 1, wherein the liquid crystal display panel has a smectic liquid crystal between a pair of substrates. 11. The liquid crystal display panel comprises nematic liquid crystal between a pair of substrates.
A lighting device for the liquid crystal display device described. 12. The lighting device for a liquid crystal display device according to claim 1, wherein the liquid crystal display panel has a ferroelectric liquid crystal between a pair of substrates. 13. The illumination device for a liquid crystal display device according to claim 1, wherein the liquid crystal display panel has an antiferroelectric liquid crystal between a pair of substrates. 14. The lighting device for a liquid crystal display device according to claim 1, wherein the liquid crystal display panel has a chiral nematic liquid crystal between a pair of substrates. 15. The illumination device for a liquid crystal display device according to claim 1, wherein at least one pair of the hot cathode tubes symmetrically arranged is turned off.