JPH11135291A - Light modulating device for liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light modulating device for a liquid crystal display for a vehicle, which can automatically adjust brightness of a screen in compliance with a wave length characteristics of an ambient light source. SOLUTION: By switching a photo sensor from 101 to 103 depending on the circumstances such as day time or night time for instance, by measuring ambient brightness of a liquid crystal display using a photo sensor 101 to 103 which complies with a wave length distribution characteristics of an ambient light source, by actuating an inverter 107 intermittently in accordance with the brightness and by varying brightness of a fluorescent tube 109, brightness of the liquid crystal display is automatically varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a dimming control for a liquid crystal display used in a vehicle, which automatically adjusts the brightness of a screen to an optimum brightness according to the surrounding brightness. Related to the device.

[0002]

2. Description of the Related Art A conventional light control device for a liquid crystal display is:
As shown in FIG. 2, a fluorescent tube 2 is provided according to the brightness of external light.
06 is automatically adjusted. The photo sensor 20 receives light from the outside and converts the brightness into an arbitrary electric signal (for example, a voltage value, a current value, etc.).
1, a photosensor circuit 202 for converting a signal from the photosensor to a DC voltage having a predetermined voltage value, a triangular wave generating circuit 203 for generating a triangular wave having a constant frequency and a constant amplitude, and a photosensor circuit 202. The comparator 204 compares the output DC voltage value with the voltage value of the triangular wave output from the triangular wave generation circuit 203 to generate a pulse wave having a constant frequency, and a predetermined voltage corresponding to the pulse wave output from the comparator 204. An AC voltage having a cycle and a voltage is generated, and this AC voltage is
6, an inverter 205 for lighting and driving, a liquid crystal panel 207 for displaying characters, images, and the like;
07 illuminates from the back side and provides a screen brightness
6 is comprised.

Since the liquid crystal panel 207 is not a self-luminous element for converting electric energy to light, a liquid crystal display using the liquid crystal panel 207 as a display means is a liquid crystal panel 207.
It is necessary to gain screen brightness by illuminating from behind. In a general liquid crystal display, a small and highly efficient cold cathode fluorescent tube constituting a backlight is mounted between a diffusion plate and a reflection plate, and this is used as a surface light source to illuminate from the back side of the liquid crystal panel 207. Therefore, dimming of the liquid crystal display means dimming of the fluorescent tube.

The pulse wave output from the comparator 204 has a signal period ratio between the high potential level and the low potential level of the rectangular wave corresponding to the difference between the brightness of the external light and the screen brightness of the liquid crystal panel 207. (Pulse width modulation output) in which the (duty ratio) changes. That is, this pulse width modulated output is supplied to the inverter 205 as a pulse wave. The duty ratio of the pulse wave changes according to the result of comparing the DC voltage value input from the photosensor circuit 202 with the voltage value of the triangular wave input from the triangular wave generation circuit 203.

Next, the operation of such a conventional light control device for a liquid crystal display will be described with reference to the drawings.

First, the photosensor 201 receives light from the outside, converts the brightness of the light into an arbitrary electric signal (for example, a voltage value, a current value, etc.) and outputs the signal to the photosensor circuit 202.

[0007] The photosensor circuit 202 converts the electric signal output from the photosensor 201 into a DC voltage having a predetermined voltage value, and inputs the DC voltage to one input terminal of the comparator 204.

Further, the triangular wave generating circuit 203 generates a triangular wave having a constant frequency and a constant amplitude, and inputs the generated triangular wave to the other input terminal of the comparator 204.

Here, the comparator 204 compares the DC voltage value input from the photosensor circuit 202 with the voltage value of the triangular wave input from the triangular wave generating circuit 203, and generates a pulse wave of a constant frequency. .

Then, the inverter 205 operates when the pulse wave output from the comparator 204 is at the high potential level and stops when the pulse wave is at the low potential level.
The pulse wave output from the inverter 205 causes the inverter 205
Is operated intermittently, and the brightness of the fluorescent tube 206 is adjusted according to the length of the intermittent operation, that is, by changing the ratio between the high potential level and the low potential level of the output of the comparator 204.

When the brightness of the fluorescent tube 206 changes, the liquid crystal panel 207 displays the screen by transmitting the light generated by the fluorescent tube 206, so that the brightness of the liquid crystal screen changes.

Therefore, the brightness of the screen changes according to the brightness of the external light around the liquid crystal display. As a result, the user of the liquid crystal display can automatically obtain the optimum screen brightness according to the surrounding brightness.

[0013]

However, the conventional light control device for a liquid crystal display has a problem in that the wavelength distribution characteristics of the surrounding light source change (that is, daytime sunlight, nighttime streetlights, illumination in a tunnel, illumination in a vehicle, etc.). Fluorescent light, etc.) and a single photosensor, the wavelength sensitivity characteristics of the photosensor differ from the wavelength distribution characteristics of the surrounding external light, making it impossible to measure the brightness properly and making the LCD highly accurate. There was a problem that the brightness of the monitor screen could not be adjusted.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a dimming device for a liquid crystal display used in a vehicle, which automatically adjusts the brightness of a screen according to the wavelength distribution characteristics of a surrounding light source.

[0015]

In order to achieve the above-mentioned object, a dimming device for a liquid crystal display according to the present invention comprises: a plurality of photosensors for measuring ambient brightness having different sensitivity characteristics depending on wavelength; A changeover switch for switching these photosensors in accordance with the wavelength distribution characteristics of the external light to be generated, a triangular wave generating circuit for generating a triangular wave having a constant frequency and a constant amplitude, and comparing the levels of the triangular wave and the output of the changeover switch. A comparator that outputs a pulse wave of a constant frequency, and an inverter that drives the fluorescent tube to light up in accordance with the pulse wave output from the comparator.

[0016]

Next, a light control device for a liquid crystal display according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a light control device for a liquid crystal display according to the present invention.

The light control device for a liquid crystal display according to the present invention comprises:
As shown in FIG. 1, a first photo sensor 101 that receives sunlight from the outside and converts brightness into an arbitrary electric signal (for example, a voltage value, a current value, or the like), and a first photo sensor 101 A first photosensor circuit 102 converts a signal from the sensor 101 into a DC voltage having a predetermined voltage value, and receives an external light to change the brightness to an arbitrary electric signal (for example, a voltage value, a current value). Second photosensor 10 for converting
3, a second photosensor circuit 104 for converting a signal from the second photosensor 103 into a DC voltage of a predetermined voltage value, and an external device, for example, a headlight switch that is turned off in conjunction with a switch of the headlight. The output of the first photosensor circuit 102 is output to a comparator 107 to be described later when the headlights are lit, that is, when the headlights are lit, that is, at night or in a tunnel. A changeover switch 105 for performing switching, a triangular wave generating circuit 106 for generating a triangular wave having a constant frequency and a constant amplitude, and a changeover switch 105
A comparator 107 that compares the DC voltage value output from the comparator with the voltage value of the triangular wave output from the triangular wave generation circuit 106 and generates a pulse wave of a constant frequency, and a predetermined signal corresponding to the pulse wave output from the comparator 107 The inverter 1 generates an AC voltage having a period and a voltage, and applies the AC voltage to a fluorescent tube 108 described later to drive the lamp.
08, a liquid crystal panel 110 for displaying characters, images, and the like,
A fluorescent tube 109 illuminates from the back side of the liquid crystal panel 110 and provides screen brightness. This fluorescent tube 10
Reference numeral 9 is arranged so as to illuminate the screen by illuminating the liquid crystal panel 110 from behind.

The maximum sensitivity wavelength of the first photosensor 101 matches the wavelength distribution characteristic of sunlight, and the maximum sensitivity wavelength of the second photosensor 103 is artificial light, at night or in a car in a tunnel. Lighting and lights coming from outside the vehicle (for example, street lights and tunnel lighting in the driver's seat,
It matches the wavelength distribution characteristics of the rear seats and buses of wagons and the like (in the case of fluorescent lights).

The pulse wave output from the comparator 107 has a signal period ratio between the high potential level and the low potential level of the rectangular wave corresponding to the difference between the brightness of the external light and the screen brightness of the liquid crystal panel 110. (Pulse width modulation output) in which the (duty ratio) changes. That is, this pulse width modulated output is supplied to the inverter 108 as a pulse wave. The duty ratio of this pulse wave is determined by the DC voltage value obtained from the first photosensor circuit 102 or the second photosensor circuit 104 switched by the changeover switch 105 and the triangular wave input from the triangular wave generation circuit 106. It changes according to the result of comparing the voltage values.

Next, the operation of the light control device for a liquid crystal display of the present invention will be described with reference to the drawings.

First, the first photosensor 101 receives sunlight from the outside and converts the brightness into an arbitrary electric signal (for example, a voltage value, a current value, etc.). Output to

The first photo sensor circuit 102 converts the electric signal from the first photo sensor 101 into a DC voltage having a predetermined voltage value, and the voltage is changed by the changeover switch 10.
5 is input.

The second photosensor 103 receives light from the outside and changes the brightness to an arbitrary electric signal (for example,
(A voltage value, a current value, and the like) and output the second photosensor circuit 104.

Then, the second photosensor circuit 104 converts the signal from the second photosensor 103 into a DC voltage having a predetermined voltage value, and the voltage is input to the changeover switch 105.

The changeover switch 105 operates in conjunction with an external device, for example, a headlight switch, to turn off the output of the first photosensor circuit 102 during the daytime when the headlight is turned on. That is, the second photosensor circuit 10 is used at night or in a tunnel.
The switching is performed so that the output of No. 4 can be input to one input terminal of the comparator 107.

The triangular wave generating circuit 106 generates a triangular wave having a constant frequency and a constant amplitude. The triangular wave is input to the other input terminal of the comparator 107.

Here, the comparator 107 compares the DC voltage value input from the changeover switch 105 with the voltage value of the triangular wave input from the triangular wave generating circuit 106, and generates a pulse wave of a constant frequency.

Then, the inverter 108 operates when the pulse wave output from the comparator 107 is at the high potential level and stops when the pulse wave is at the low potential level.
07, the pulse wave output from the inverter 108
Is operated intermittently, and the brightness of the fluorescent tube 109 is varied according to the length of the intermittent operation, that is, by changing the ratio between the high potential level and the low potential level of the output of the comparator 107.

If the brightness of the fluorescent tube 109 changes, the liquid crystal panel 110 displays the screen by transmitting the light generated by the fluorescent tube 109, so that the brightness of the liquid crystal screen changes.

Therefore, in the liquid crystal display dimming apparatus used in a vehicle according to the present invention, the brightness of the surroundings of the liquid crystal display is changed by switching a plurality of photosensors according to the situation such as daytime or nighttime. To
The brightness of the liquid crystal display screen was measured by using a photosensor that matched the wavelength distribution characteristics of the surrounding light source and intermittently operating the inverter 107 according to the brightness to change the brightness of the fluorescent tube 109. Can be automatically changed, thereby optimizing the brightness of the screen.

[0031]

As described above, according to the light control device for a liquid crystal display of the present invention, the brightness around the liquid crystal display is changed to the wavelength distribution characteristic of the light source by switching a plurality of photosensors according to the situation. The brightness of the liquid crystal display screen can be changed automatically because the inverter is operated intermittently according to the brightness and the brightness of the fluorescent tube is changed by measuring with the matched photo sensor. As a result, the brightness of the screen with respect to the surrounding brightness can always be set to the optimum brightness.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a light control device for a liquid crystal display according to the present invention.

FIG. 2 is a block diagram showing a conventional light control device for a liquid crystal display.

[Explanation of symbols]

 Reference Signs List 101 first photosensor 102 first photosensor circuit 103 second photosensor 104 second photosensor circuit 105 changeover switch 106 triangular wave generation circuit 107 comparator 108 inverter 109 fluorescent tube 110 liquid crystal panel

Claims (1)

[Claims] A plurality of photosensors for measuring ambient brightness having different sensitivity characteristics depending on wavelengths; a changeover switch for switching these photosensors in accordance with a wavelength distribution characteristic of irradiating external light; A triangular wave generating circuit for generating a triangular wave of a frequency and a constant amplitude, a comparator for comparing the level of the triangular wave with the output of the changeover switch and outputting a pulse wave of a constant frequency, and a fluorescent light corresponding to the pulse wave output from the comparator A dimmer for a liquid crystal display, comprising: an inverter for driving a tube to light.