JP2002110394A - Light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source device that is improved in display quality by restraining deterioration in the display image quality caused by dimmer control of the light source lamp, without involving enlargement of the device scale and increase of the product cost. SOLUTION: The light source comprises a power source 10 for supplying a prescribed direct current voltage V1, a DC-DC converter 20 that converts the direct current voltage V1 into prescribed direct current voltages V3, V4, V5 for working as the power source voltage for driving the function circuit part of the display device and outputs continuously, a current regulating circuit 100 that regulates the load condition in the DC-DC converter 20, and a light source driving control part LU and a display driving control part DU that constitute the function circuit part. The current regulating circuit 100 comprises a bypass for discharging the driving current 12 supplied to the transformer driving frequency control circuit 30 to the grounding potential in accordance with the signal timing of a dimming pulse Sp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source device,
In particular, the present invention relates to a light source device that can be favorably applied as a backlight of a liquid crystal display device and that can adjust the brightness of a light source lamp by a pulse dimming method.

[0002]

2. Description of the Related Art In recent years, information communication devices such as personal computers, car navigation systems, digital video cameras, and portable information terminals have become remarkably widespread. In such information communication devices, a display device plays a large role as an input / output interface. In recent years, display devices have become thin, space-saving,
Liquid crystal display devices (LCDs) having features such as power saving are rapidly spreading.

In such a liquid crystal display device, a display image is clearly recognized even in a dark environment, and the rear side of a transmissive liquid crystal display panel is provided so as to improve the color developability in a color display. One having a configuration in which a backlight is arranged is often used. Here, a flat white light source is generally used as the backlight, and as a configuration therefor, a fluorescent tube (cold cathode tube) and a flat light guide plate, or
A configuration including a flat fluorescent tube or the like is applied.

[0004] The schematic configuration of a conventional liquid crystal display device will be briefly described below. Here, as a method of adjusting the brightness of the backlight, a method of adjusting the amount of current (current value) flowing through the backlight (cold cathode tube) and a method of adjusting the time during which the current flows are known. However, in the former, there are problems such as a narrow dimming range and deterioration of the lighting start-up characteristic due to insufficient current. Therefore, the latter dimming method (the latter adjusts the time for flowing the current by the signal width of the pulse signal). Pulse dimming method) is frequently used.

FIG. 3 is a block diagram showing a schematic configuration of a liquid crystal display device having a pulse dimming type light source device. As shown in FIG. 3, the conventional liquid crystal display device is roughly divided into a power supply 10 for supplying a predetermined DC voltage V1, and a DC voltage V3, V4 having a predetermined signal level.
DC-DC converter 20 that converts to V5 and outputs constantly
And a light source drive control unit LU and a display drive control unit DU driven based on the DC voltages V3, V4, V5.

The light source drive control unit LU uses the DC voltage V3 supplied from the DC-DC converter 20 as a power supply voltage,
A transformer driving frequency control circuit 30 that outputs a control signal (St) for adjusting and controlling the driving frequency of the inverter transformer 50 based on the dimming pulse Sp;
current amplifying circuit 40 for amplifying t) to a predetermined signal level
And an inverter transformer 50 that converts a DC voltage V1 supplied from the power supply 10 into an AC voltage V2, sets a predetermined frequency (period) based on the control signal St, and outputs the frequency to the cold-cathode tube 60. And a load current detection circuit 70 for detecting a drive current I1 flowing through the cathode tube 60.

On the other hand, the display drive control unit DU has a DC-DC
An LCD drive signal processing circuit 80 that performs drive control for displaying image information on the liquid crystal display panel 90 using the DC voltage V4 supplied from the converter 20 as a power supply voltage;
A liquid crystal display panel (LCD panel) 90 for displaying predetermined image information based on a control signal Sc output from the LCD drive signal processing circuit 80, using a DC voltage V5 supplied from the DC converter 20 as a power supply voltage; It is configured with.

In the liquid crystal display device having such a configuration, the DC voltage V1 supplied from the power supply 10 is converted into the AC voltage V2 of a predetermined frequency by the inverter transformer 50.
Is output to the cold-cathode tube 60, so that the cold-cathode tube 60 is driven to blink. Here, the inverter transformer 5
0 is an AC voltage output to the cold-cathode tube 60 based on a control signal St whose output is controlled by turning on / off the transformer drive frequency control circuit 30 in response to a dimming pulse Sp input from outside the device. The frequency of V2 is set and controlled, and the driving frequency of the cold cathode tube 60 is adjusted.

That is, the transformer driving frequency control circuit 3
0 is in the ON state, the inverter transformer 50
Outputs the AC voltage V2 to the cold cathode tube 60, and the cold cathode tube 60 is turned on. On the other hand, when the transformer drive frequency control circuit 30 is in the OFF operation, the inverter transformer 50
Is cut off, and the cold-cathode tube 60 is turned off. Thus, by controlling the cycle of the ON / OFF operation of the transformer drive frequency control circuit 30 by the dimming pulse Sp, the lighting time of the cold cathode tube 60 is controlled to adjust the brightness (brightness) of the backlight. You. Here, if the cycle (frequency) of the dimming pulse Sp is low, the blinking of the cold-cathode tube 60 is slowed down so that humans can perceive it. Therefore, a frequency of about several tens to several hundreds of hertz is used as the normal light control pulse Sp.

[0010]

However, the above-mentioned liquid crystal display device has the following problems. (1) In the above-described liquid crystal display device, the dimming pulse S
The transformer drive frequency control circuit 30 is turned ON /
Since there was a method of controlling the lighting time of the cold-cathode tube 60 to perform dimming by performing the OFF operation, the power supply voltage (DC voltage V3) supplied from the DC-DC converter 20 in the transformer drive frequency control circuit 30 was used. ) Is interrupted in synchronization with the dimming pulse Sp, so that a current fluctuation occurs.
Therefore, the DC-DC
Other power supply voltages (DC voltages V4 and V5) output from the converter 20 also fluctuate in synchronization with the dimming pulse Sp,
Noise occurs in the image information displayed on the LCD panel,
There is a problem that the display image quality is deteriorated.

(2) Further, in order to suppress the problem described in the above (1), the DC-DC converter 20 is separately provided in each of the light source drive control unit LU and the display drive control unit DU, and the DC voltage V3 It is conceivable to separate the electrical relationship between the DC voltage V4 and V5, but in this case, DC-DC
It is necessary to increase the number of converters, which causes a problem that the size of the device (or mounting space) is increased, and the cost of products is increased due to an increase in the number of components.

(3) In order to suppress the problem described in the above (1), the primary input of the inverter transformer 50 is controlled to be conductive / interrupted while the transformer drive frequency control circuit 30 is always turned on. It is conceivable to control the lighting time of the cold-cathode tube 60. However, compared with the case where the transformer drive frequency control circuit 30 is turned on / off, the large-capacity DC voltage V
1 has a problem that it is not practically preferable because the switching loss at the time of conducting / cutting off 1 is extremely large.

(4) Further, in order to suppress the problem described in the above (1), a ripple filter may be provided in the supply path of the output voltage to absorb and reduce the fluctuation.
As described above, since the noise appearing in the liquid crystal display panel is synchronized with the dimming pulse Sp, the ripple filter can favorably absorb the voltage fluctuation in the frequency band of about several tens to several hundreds of hertz described above. In this case, it is necessary to set the capacitance of the capacitor to be extremely large, which causes a problem that the size of the device is increased and the product cost is increased.

Accordingly, an object of the present invention is to solve such a problem, and the display quality is deteriorated due to the dimming control of the light source lamp without increasing the size of the device or increasing the product cost. It is an object of the present invention to provide a light source device capable of improving display quality by suppressing image quality.

[0015]

According to a first aspect of the present invention, there is provided a light source device comprising: a light source lamp; a light source lamp drive control means for supplying a driving voltage of a predetermined frequency to the light source lamp to control lighting; Operation and non-operation are controlled based on a pulse, a drive frequency control unit that generates a control signal that variably controls the frequency of the drive voltage, and at least the drive frequency based on a power supply voltage supplied from a single power supply. Power supply means for generating a first power supply voltage for operating the control means, and a second power supply voltage for driving and controlling other functional circuit units other than the drive frequency control means, and constantly outputting the second power supply voltage; A bypass circuit to which the first power supply voltage is supplied from the power supply means and a current is applied,
A current is not applied to the bypass circuit when the drive frequency control means is operating, and a current is applied to the bypass circuit when the drive frequency control means is not operating.

That is, there is provided a power supply means for controlling the driving of the light source lamp from a single power supply and for generating a power supply voltage for other functional circuits, and the driving frequency control means is provided in accordance with dimming control of the light source lamp. In the light source device in which the operation and the non-operation state are controlled, when the drive frequency control unit is not operated, the drive current adjustment unit causes the current to flow from the power supply unit to the bypass circuit, thereby reducing the first power supply voltage. Adjustment control is performed so that the supply state of the drive current supplied from the power supply means is made substantially constant.

Thus, the fluctuation of the first power supply voltage generated by the power supply means is suppressed, and the fluctuation of the second power supply voltage output to the other functional circuit section is suppressed and stabilized. Therefore, it is possible to suppress the occurrence of functional failure or failure (deterioration of display image quality, etc.) due to the intrusion of noise into a functional circuit unit such as an image display unit during dimming control of the light source lamp.

In the light source device according to a second aspect of the present invention, the bypass circuit includes a bypass for the current and a load provided on the bypass, and the bypass circuit is provided in response to the dimming pulse. It is characterized in that the power supply means controls the application of current to the load. That is, the operation state of the drive frequency control means is controlled in accordance with the dimming pulse, and the application of current to the load of the bypass circuit is controlled in accordance with the dimming pulse, so that the load of the bypass circuit is controlled. Is controlled in accordance with the operation state of the drive frequency control means.

As a result, fluctuations in the first power supply voltage are suppressed, so that fluctuations in the second power supply voltage output to the other functional circuit sections are stabilized, and functional failure in the other functional circuit sections is prevented. And the occurrence of defects can be suppressed,
A relatively simple circuit configuration that controls the application of current to the load of the bypass circuit in accordance with the dimming pulse can be configured with a relatively simple circuit configuration. Obtainable.

Further, a light source device according to a third aspect of the present invention is characterized in that, in the above configuration, the other functional circuit section includes at least a drive control circuit of a liquid crystal display device. That is, in a liquid crystal display device having a backlight on the back side of a transmissive liquid crystal display panel, even if dimming control for adjusting the brightness of the backlight (light source lamp) is performed, the display on the liquid crystal display panel is performed. It is possible to prevent noise from being mixed in the processed image and thereby deteriorating the image quality.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a light source device according to the present invention will be described in detail by showing embodiments. FIG.
1 is a block diagram illustrating a schematic configuration of a liquid crystal display device including a light source device according to the present invention. Here, components equivalent to those of the above-described related art will be described with the same reference numerals.

As shown in FIG. 1, the liquid crystal display device according to the present embodiment has a power supply 10 for supplying a predetermined DC voltage V1.
And converting the DC voltage V1 into predetermined DC voltages V3 (first power supply voltage), V4, and V5 (second power supply voltage) serving as power supply voltages for driving the functional circuit unit of the display device. DC-DC converter (power supply means) 20 that outputs constantly
A current adjustment circuit (drive current adjustment means) 100 for adjusting a load state of the DC-DC converter 20, that is, a supply state of the drive current I2, and a light source drive control unit LU and a display drive control unit constituting a functional circuit unit (Other functional circuit unit) DU.

Hereinafter, each component will be described in detail. The light source drive control unit LU includes a transformer drive frequency control circuit (drive frequency control means) 30 as in the configuration shown in FIG.
, A current amplifying circuit 40, an inverter transformer (light source lamp drive control means) 50, and a cold cathode tube (light source lamp) 6
0, a current detection circuit (drive current adjusting means) 70. Transformer drive frequency control circuit 30
Is an oscillator that uses the DC voltage V3 supplied from the DC-DC converter 20 as a power supply voltage and repeats ON / OFF operation based on a dimming pulse Sp input from outside the device, and is generated by the inverter transformer 50. A control signal (St) for setting and controlling the frequency of the AC voltage V2 is output.

The current amplifying circuit 40 amplifies the control signal (St) output from the transformer driving frequency control circuit 30 to a predetermined signal level suitable for controlling the driving of the inverter transformer 50. The inverter transformer 50 converts the DC voltage V1 supplied from the power supply 10 into an AC voltage V2 and, based on the control signal St output from the transformer drive frequency control circuit 30, controls the frequency (period) of the AC voltage V2. ) Is set and output to the cold cathode tube 60. The load current detection circuit 70 detects the drive current I1 flowing through the cold cathode tube 60 based on the AC voltage V2 output from the inverter transformer 50, and sends the load state of the cold cathode tube 60 to the transformer drive frequency control circuit 30. give feedback.

On the other hand, the display drive control unit DU includes an LCD drive signal processing circuit 80 and a liquid crystal display panel 90 as in the configuration shown in FIG. The LCD drive signal processing circuit 80 is
The drive control for displaying predetermined image information on the liquid crystal display panel 90 is performed using the DC voltage V4 supplied from the power supply as a power supply voltage. In the liquid crystal display panel 90, the liquid crystal pixels are arranged in a matrix, the DC voltage V5 supplied from the DC-DC converter 20 is used as a power supply voltage, and based on a control signal Sc output from the LCD drive signal processing circuit 80. By applying a signal voltage based on the image signal to the selected liquid crystal pixel, predetermined image information is displayed.

Next, a current adjusting circuit applied to the light source device according to the present invention will be described with reference to the drawings. FIG. 2 is a circuit diagram illustrating a configuration example of a current adjustment circuit applied to the liquid crystal display device according to the present embodiment. Note that the current adjustment circuit shown here is an example, and it goes without saying that the current adjustment circuit may have another circuit configuration as long as it has a function equivalent to the function described below. As shown in FIG. 2, the current adjustment circuit 100 includes, for example, a dimming pulse Sp.
INV that inverts and outputs a signal, and a transistor switch Tr that performs ON / OFF operation according to the inverted signal
During the ON operation of the transistor switch Tr, a current having a current value equivalent to the drive current I2 supplied to the transformer drive frequency control circuit 30 is discharged to a predetermined potential (ground potential) via the transistor switch Tr. , And a load resistor R1 having a resistance value set.

That is, the load resistor R1 and the transistor switch Tr constitute a bypass for the drive current I2,
When the transformer driving frequency control circuit 30 is turned on by the signal timing of the dimming pulse Sp, the transistor switch Tr is turned off to cut off the bypass path, and when the transformer driving frequency control circuit 30 is turned off, the transistor switch Tr is turned off. Tr is turned on to form a bypass, and the drive current I2 is discharged to the ground potential.

Thus, in the liquid crystal display device having the above-described configuration, the transformer driving frequency control circuit 30
In the N state, the lighting of the cold-cathode tube 60 is controlled based on the AC voltage V2 output from the inverter transformer 50, while the transformer drive frequency control circuit 30
When the state becomes the F state, the output of the AC voltage V2 from the inverter transformer 50 is cut off, and the cold-cathode tube 60 is turned off. At this time, the drive current I2 output from the DC-DC converter 20 is substantially uniform (with a substantially constant current amount) in the transformer drive frequency control circuit 30 or the current adjustment circuit 100 according to the dimming pulse Sp. Since it always flows down, the O
The current fluctuation caused by the N / OFF operation is greatly suppressed,
The power supply voltage (DC voltage V) supplied to the display drive control unit DU
4, V5) can be stabilized, and the deterioration of the display image quality due to the entry of noise into the display drive control unit DU during the dimming control of the cold-cathode tube 60 can be suppressed.

Further, since the current adjusting circuit 100 can be constituted by a relatively simple and integrable circuit including the load resistor R1, the inverter INV, and the transistor switch Tr, the scale of the device (or mounting space) can be reduced.
Increase and product cost can be suppressed. Further, in the liquid crystal display device according to the present embodiment, when the above-described turning on / off control of the cold cathode tube 60 is performed, that is, the driving current output from the DC-DC converter 20 based on the dimming pulse Sp. When switching the current path of I2, it is conceivable that a voltage fluctuation occurs for a very short time at the switching timing, but since the frequency component of the voltage fluctuation becomes higher than the dimming pulse Sp, a relatively small capacitor is required. By providing the used simple ripple filter in the supply path of the power supply voltage (DC voltages V3, V4, V5), the above-described voltage fluctuation can be favorably absorbed and mitigated, thereby further reducing the size of the device configuration and the product cost. Can be reduced.

In the embodiment described above, the light source device according to the present invention is applied to a liquid crystal display device, and a DC-DC
The configuration has been described in which the converter 20 constantly outputs the predetermined power supply voltages V3, V4, and V5 simultaneously to the light source drive control unit LU and the display drive control unit DU, but the present invention is not limited to this. Therefore, as another functional circuit unit, instead of the display drive control unit DU, an arithmetic processing unit (CP
U) or a hard disk drive, etc.
In this case, it is possible to suppress the influence of voltage fluctuations on other functional circuit units during the dimming control, thereby suppressing the occurrence of functional failure or failure.

[0031]

According to the light source device of the first aspect, the first power supply voltage for controlling the driving of the light source lamp from a single power supply,
And a light source device provided with a power supply unit for generating a second power supply voltage for another functional circuit, wherein the power supply unit is provided in accordance with an operation state of the drive frequency control unit (ie, dimming control of the light source lamp). No current is applied to the bypass circuit when the drive frequency control means is operating, and when the drive frequency control means is not operating,
Since the adjustment is controlled so as to apply the current to the bypass circuit, the drive current based on the first power supply voltage is stabilized, and the fluctuation of the second power supply voltage output to other functional circuit units is suppressed to be stable. It is possible to suppress the occurrence of functional failure or failure (deterioration in display image quality, etc.) due to the incorporation of noise into a functional circuit unit such as an image display unit during dimming control of the light source lamp.

Further, according to the light source device of the second aspect,
The bypass circuit includes a bypass path and a load, and the application of current to the load is controlled by the power supply unit according to the dimming pulse, so that the application of current to the load of the bypass circuit corresponds to the operation state of the drive frequency control unit. Will be controlled.
Thereby, the fluctuation of the first power supply voltage is suppressed.
By stabilizing the fluctuation of the second power supply voltage output to the other functional circuit unit, it is possible to suppress the occurrence of a functional failure or failure in the other functional circuit unit, and to bypass the dimming pulse according to the dimming pulse. Since it can be configured with a relatively simple circuit configuration that controls the application of current to the load of the circuit,
The above effects can be obtained while suppressing an increase in the scale of the apparatus and an increase in the product cost.

Further, according to the light source device of the third aspect, in a transmissive liquid crystal display device having a backlight on the back side of a transmissive liquid crystal display panel, a control for adjusting the luminance of the backlight (light source lamp). Even when the light control is performed, it is possible to prevent the image displayed on the liquid crystal display panel from being mixed with noise and deteriorating the image quality.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a liquid crystal display device including a light source device according to the present invention.

FIG. 2 is a circuit diagram illustrating a configuration example of a current adjustment circuit applied to the liquid crystal display device according to the embodiment.

FIG. 3 is a block diagram illustrating a schematic configuration of a liquid crystal display device including a pulse light control type light source device according to the related art.

[Explanation of symbols]

 Reference Signs List 10 power supply 20 DC-DC converter 30 transformer drive frequency control circuit 40 current amplifier circuit 50 inverter transformer 60 cold cathode tube 70 load current detection circuit 80 drive signal processing circuit 90 liquid crystal display panel 100 current adjustment circuit DU display drive control unit LU light source drive Control unit Sp dimming pulse

Claims (3)

[Claims] A light source lamp; a light source lamp drive control means for supplying a drive voltage of a predetermined frequency to the light source lamp to control lighting; and controlling operation and non-operation based on a predetermined dimming pulse; Drive frequency control means for generating a control signal for variably controlling the frequency of the drive voltage; and at least a first power supply voltage for operating the drive frequency control means based on a power supply voltage supplied from a single power supply; Power supply means for generating and constantly outputting a second power supply voltage for driving and controlling other functional circuit units other than the drive frequency control means; and supplying the first power supply voltage from the power supply means And a bypass circuit to which a current is applied.When the drive frequency control means is operating, no current is applied to the bypass circuit, and when the drive frequency control means is not operated. , The light source apparatus characterized by so as to apply a current to the bypass circuit. 2. The bypass circuit according to claim 1, further comprising: a bypass path for the current, and a load provided on the bypass path, wherein the power supply unit controls application of a current to the load in accordance with the dimming pulse. The light source device according to claim 1, wherein the light source device is configured to be operated. 3. The light source device according to claim 1, wherein the other functional circuit unit includes at least a drive control circuit of a liquid crystal display device.