JPH10240145A - Back light device for liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optically adjust white balance on a liquid crystal display device. SOLUTION: This back light device is provided with a source of light 19 consisting of a white fluorescent tube 1A, a purple colored fluorescent tube 1B and a green colored fluorescent tube 1C, and a brightness control unit 20 permitting to independently control the brightness of the white fluorescent tube 1A and the colored fluorescent tubes 1B, 1C. The brightness control unit 20 is provided with an inverter power supplies 2A-2C for supplying electric power to a white fluorescent tube 1A and the colored fluorescent tube 1B and 1C, and an output voltage regulator 4 for adjusting the output voltage of the inverter power supplies 2A-2C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device used for a transmission type liquid crystal display, and more particularly to a backlight device capable of adjusting a white balance.

[0002]

2. Description of the Related Art As a conventional backlight device, there is one described in, for example, Japanese Patent Application Laid-Open No. 3-27802. This backlight device is provided with a light source composed of a plurality of white fluorescent tubes and a luminance control unit that can independently control the luminance of each white fluorescent tube, and can make the luminance of the entire light source uniform. It is.

FIG. 8 is a functional block diagram showing the conventional backlight device. Hereinafter, description will be made based on this drawing.

A conventional backlight device includes a light source 23 including four white fluorescent tubes 8A to 8D and a white fluorescent tube 8A to 8D.
And a brightness control unit 24 capable of independently controlling the 8D brightness. The brightness control unit 24 includes a white fluorescent tube 8A.
Inverter power supplies 9A to 9D for supplying power to
Luminance sensor 10 for detecting the luminance of white fluorescent tubes 8A to 8D
A to 10D and the inverter power supply 9 based on the luminance of the white fluorescent tubes 8A to 8D detected by the luminance sensors 10A to 10D.
And an output voltage regulator 11 for adjusting output voltages of A to 9D.

[0005] DC power is supplied from a DC power supply 12 to the inverter power supplies 9A to 9D. White fluorescent tube 8A ~
8D is connected to the corresponding inverter power supplies 9A to 9D, and the brightness is adjusted by increasing or decreasing the output of the inverter power supplies 9A to 9D. Luminance sensors 10A to 10D
Feeds back the detection signal to the output voltage regulator 11,
The output voltage regulator 11 controls the outputs of the inverter power supplies 9A to 9D.

Next, the operation will be described. In order to make the brightness of the liquid crystal display uniform, it is necessary to first detect the brightness of each of the white fluorescent tubes 8A to 8D. Therefore, brightness sensors 10A to 10D are provided corresponding to the white fluorescent tubes 8A to 8D. The brightness sensors 10A to 10D correspond to the corresponding white fluorescent tubes 8A to 8D.
And outputs detection signals S4 to S7. The output voltage regulator 11 receives the detection signals S4 to S7, compares the detected luminance with a predetermined luminance, and outputs control signals D4 to D7 for correcting the difference. The inverter power supplies 9A to 9D receive the control signals D4 to D7 and supply different AC voltages L4 to L7 to the respective fluorescent tubes 8A to 8D to make the brightness of the liquid crystal display uniform.

[0007]

The first problem is that the white balance changes. The reason is red,
This is because a plurality of white fluorescent tubes emitting three wavelengths composed of green and blue are used. That is, since the emission characteristics of three wavelengths usually differ among the white fluorescent tubes, the white balance changes when a plurality of white fluorescent tubes are used simultaneously and the brightness is independently adjusted.

The second problem is that the white balance cannot be adjusted optically. The reason is that even in the same type of liquid crystal display, there is a difference in white balance depending on the color of the fluorescent tube. In particular, in the case of a monochrome liquid crystal display, it is impossible to adjust the white balance without optically correcting.

The third problem is that, when correcting white balance in a color liquid crystal display besides optically, the image quality often deteriorates. The reason is that when white balance is corrected besides optically, it is corrected electrically. The white balance is corrected by adjusting the amplitude voltage of each of the red, green, and blue video signals supplied to the liquid crystal display. At this time, the difference in the amplitude voltage for each color causes the frequency characteristics and S
Since the difference in the / N ratio occurs, the image quality deteriorates.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a backlight device for optically adjusting a white balance in a liquid crystal display.

[0011]

A backlight device according to the present invention includes a light source including a plurality of colored fluorescent tubes that become white when combined, and a luminance control unit that can independently control the luminance of the colored fluorescent tubes. It is provided. The brightness control unit may include an inverter power supply for supplying power to the colored fluorescent tube, and an output voltage regulator for adjusting an output voltage of the inverter power supply. Further, the brightness control unit includes:
An inverter power supply for supplying power to the colored fluorescent tube, a luminance sensor for detecting the luminance of the colored fluorescent tube, and a luminance sensor for detecting the luminance of the colored fluorescent tube detected by the luminance sensor so that the luminance becomes constant. An output voltage regulator for adjusting the output voltage of the inverter power supply may be provided. Further, the light source includes a white fluorescent tube, a purple colored fluorescent tube, and a green colored fluorescent tube, and the luminance control unit controls the luminance of the white fluorescent tube, the purple colored fluorescent tube, and the green colored fluorescent tube independently. May be controlled.

The white balance of the liquid crystal display is adjusted by using a plurality of colored fluorescent tubes which become white when combined as a light source and adjusting the luminance component output for each of the colored fluorescent tubes. Therefore, the white balance can be optically adjusted only by the liquid crystal display.

[0013]

1 and 2 show a first embodiment of a backlight device according to the present invention. FIG. 1 is a functional block diagram, and FIG. 2 is an external perspective view. Hereinafter, description will be made based on these drawings.

The backlight device of this embodiment comprises a white fluorescent tube 1A, a purple colored fluorescent tube 1B and a green colored fluorescent tube 1C.
Light source 19 comprising a white fluorescent tube 1A and a colored fluorescent tube 1
A brightness control unit 20 that can independently control the brightness of B and 1C
It is provided with. The brightness control unit 20 includes inverter power supplies 2A to 2C that supply power to the white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C, and an output voltage regulator 4 that adjusts output voltages of the inverter power supplies 2A to 2C. .

The output voltage regulator 4 outputs control signals D1 to D3 which can be arbitrarily set, for example, manually. The inverter power supplies 2A to 2C receive control signals D1 to D3,
Different AC voltages are supplied to the white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C based on the control signals D1 to D3. The white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C emit light by the supplied AC voltage. The light guide plate 6 uniformly diffuses light having different emission characteristics of the white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C and supplies the light to the liquid crystal panel 5.

The output voltage regulator 4 includes an inverter power supply 2A
Control signal D for controlling output AC voltages L1 to L3
1 to D3 are output. The control signals D1 to D3 are set arbitrarily. The inverter power supplies 2A to 2C receive the control signals D1 to D3, generate output AC voltages L1 to L3 according to the control signals D1 to D3, and supply them to the white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C. The white fluorescent tube 1A, the purple colored fluorescent tube 1B, and the green colored fluorescent tube 1C have an output AC voltage L
Light is emitted according to 1 to L3.

3 to 6 are graphs showing the wavelength distribution of the fluorescent tube. FIG. 3 shows a white fluorescent tube 1A, FIG. 4 shows a colored fluorescent tube 1B, FIG. 5 shows a colored fluorescent tube 1C, and FIG. It is. Hereinafter, an operation of the backlight device according to the present embodiment will be described with reference to FIGS.

As shown in FIG. 3, the white fluorescent tube 1A has red,
It emits three wavelengths consisting of three wavelengths, green and blue. Then, according to the three primary colors of light, it emits white light formed by combining the three colors of light. Therefore, the purple colored fluorescent tube 1
By combining with the B and green colored fluorescent tubes 1C and synthesizing the respective lights, the white balance can be adjusted.

The output voltage regulator 4 outputs control signals D1 to D3 arbitrarily set. The control signals D1 to D3 are DC voltages such as 0 to 5 V, for example, and the inverter power supplies 2A to
It can control the output voltage of 2C. The output voltage regulator 4 includes, for example, a variable resistor or a microcomputer and a D
/ A converter can be realized. Inverter power supplies 2A to 2C receive control signals D1 to D3, generate output AC voltages L1 to L3 proportional to control signals D1 to D3, and correspond to white fluorescent tube 1A and colored fluorescent tube 1B,
Supply to 1C. A white fluorescent tube 1A and a colored fluorescent tube 1B,
1C emits light with a luminance proportional to the supplied output AC voltages L1 to L3.

Here, the light emission characteristics of the white fluorescent tube 1A are shown in FIG.
As shown in the figure, light is emitted at red, green and blue wavelengths. The colored fluorescent tube 1B emits light at red and blue wavelengths as shown in FIG.
The colored fluorescent tube 1C emits light at a green wavelength as shown in FIG. The respective color luminance output levels Y1 to Y3 of the white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C are all synthesized, and the light emission characteristics of each color luminance output level Y4 of the light source 19 shown in FIG. 6 are obtained. Then, the combined light of the light source 19 is sent to the light guide plate 6 and is transmitted to the light guide plate 6.
The light is uniformly diffused in the plane and supplied to the liquid crystal panel 5. As described above, the white balance can be controlled by changing the luminance of the light emission characteristics of the white fluorescent tube 1A and the color fluorescent tubes 1B and 1C and combining the luminance components.

FIG. 7 is a functional block diagram showing a second embodiment of the backlight device according to the present invention. Hereinafter, description will be made based on this drawing. However, the same parts as those in FIG.

The backlight device of this embodiment includes a white fluorescent tube 1A, a purple colored fluorescent tube 1B, and a green colored fluorescent tube 1C.
Light source 19 comprising a white fluorescent tube 1A and a colored fluorescent tube 1
A brightness control unit 21 that can independently control the brightness of B and 1C.
It is provided with. The luminance control unit 21 includes inverter power supplies 2A to 2C that supply power to the white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C, and luminance sensors 7A to 7C that detect the luminance of the white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C. When,
An output voltage regulator 4 'that adjusts the output voltage of the inverter power supplies 2A to 2C based on the luminance of the white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C detected by the luminance sensors 7A to 7C so that the luminance becomes constant. And

White fluorescent tube 1A and colored fluorescent tubes 1B, 1C
Below, the brightness sensors 7A to 7A to measure the respective brightness
7C is provided. The brightness sensors 7A to 7C are, for example, general optical sensors, and detect the brightness of the white fluorescent tube 1A and the colored fluorescent tubes 1B and 1C, and output the brightness detection signals S1 to S.
3 is output. The output voltage adjuster 4 ′ compares the preset setting value with the luminance detection signals S1 to S3, and controls the control signals D1 to D3 so as to correct the difference with the setting value as a target.
Is output. Therefore, by previously determining the set value of the output voltage adjuster 4 'so as to obtain an emission characteristic of an arbitrary combined light, the emission characteristic of an arbitrary combined light can be automatically adjusted. As described above, the backlight device according to the present embodiment includes:
In addition to the effects of the first embodiment, there is also an effect that any light emission characteristics can be obtained by automatic adjustment.

In the first and second embodiments, the light source is constituted by the three fluorescent tubes of white, violet and green. However, if the combined light of the colored fluorescent tubes becomes white, the fluorescent tubes are turned off. There are no restrictions on the number or color. For example, the light source may be configured only with red, purple, and green colored fluorescent tubes without using a white fluorescent tube. In FIG. 2, the arrangement of the fluorescent tubes is shown as an edge light type, but the same effect can be obtained with a direct type.

[0025]

The first effect is that the light emission characteristics can be made the same in a plurality of liquid crystal displays. The reason is that, since the luminance component output can be adjusted for each fluorescent tube with different light emitting characteristics of a plurality of colored fluorescent tubes, it is possible to adjust even if the light emitting characteristics of the fluorescent tubes of a plurality of liquid crystal displays are different. by.

The second effect is that the white balance can be optically adjusted even in a monochrome liquid crystal display or a color liquid crystal display having no white balance adjustment function in an image output device. The reason is that, in a liquid crystal display, a luminance component output can be adjusted for each fluorescent tube with different light emission characteristics of a plurality of colored fluorescent tubes, so that white balance can be optically adjusted.

The third effect is that the image quality is less deteriorated compared to a liquid crystal display having a white balance adjustment function on the video output device side. The reason is as follows. When correcting the white balance on the video output device side, the amplitude voltage of each of the red, green, and blue video signals supplied to the liquid crystal display is adjusted for electrical correction,
Correct white balance. At this time, a difference occurs in the amplitude voltage for each signal, resulting in a difference in frequency characteristics and S / N ratio. However, in the present invention, since the video signal is not affected at all by optically adjusting the white balance, deterioration of the image quality is small.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a first embodiment of a backlight device according to the present invention.

FIG. 2 is an external perspective view showing a first embodiment of a backlight device according to the present invention.

FIG. 3 is a graph showing a wavelength distribution of a white fluorescent tube in the backlight device of FIG. 1;

FIG. 4 is a graph showing a wavelength distribution of a violet colored fluorescent tube in the backlight device of FIG. 1;

FIG. 5 is a graph showing a wavelength distribution of a green colored fluorescent tube in the backlight device of FIG. 1;

FIG. 6 is a graph showing a wavelength distribution of a light source in the backlight device of FIG.

FIG. 7 is a functional block diagram showing a second embodiment of the backlight device according to the present invention.

FIG. 8 is a functional block diagram showing a conventional backlight device.

[Explanation of symbols]

 Reference Signs List 1A White fluorescent tube 1B Colored fluorescent tube [purple] 1C Colored fluorescent tube [green] 2A, 2B, 2C Inverter power supply 4, 4 'Output voltage regulator 7A, 7B, 7C Luminance sensor 19 Light source 20, 21 Luminance control unit

Claims (4)

[Claims] 1. A backlight device for a liquid crystal display, comprising: a light source including a plurality of colored fluorescent tubes that become white when combined; and a luminance control unit capable of independently controlling the luminance of the colored fluorescent tubes. 2. The liquid crystal display according to claim 1, wherein the brightness control unit includes an inverter power supply for supplying power to the colored fluorescent tubes, and an output voltage regulator for adjusting an output voltage of the inverter power supply. Backlight device. 3. The luminance control section includes an inverter power supply for supplying power to the colored fluorescent tube, a luminance sensor for detecting luminance of the colored fluorescent tube, and a luminance of the colored fluorescent tube detected by the luminance sensor. 2. The backlight device for a liquid crystal display according to claim 1, further comprising: an output voltage adjuster that adjusts an output voltage of the inverter power supply so that the luminance becomes constant based on the following. 4. The light source includes a white fluorescent tube, a purple colored fluorescent tube and a green colored fluorescent tube, and the brightness control section can independently control the brightness of the white fluorescent tube and each of the colored fluorescent tubes. 4. The backlight device for a liquid crystal display according to claim 1, 2, or 3.