JP3076184B2 - Liquid crystal display - Google Patents

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 , and more particularly to a transmission type liquid crystal having a backlight having a dimming function.
It relates to a display device.

[0002]

2. Description of the Related Art Since a liquid crystal display (LCD) is a non-light-emitting display, it is necessary to illuminate a place where external light conditions are poor. In particular, transmission type L used for liquid crystal televisions, OA terminals, etc.
The CD is equipped with a surface light source, that is, a backlight, for uniformly illuminating the LCD surface from the rear for clear display. A fluorescent lamp is mainly used as a light source of the backlight. The display image on the LCD is displayed by the light of the backlight passing through the liquid crystal panel.
The relative brightness of an image is greatly affected by the brightness of the display environment. That is, when the surroundings of the display are bright, the screen is not bright unless the screen is bright. On the other hand, when the surroundings are dark, the screen is difficult to see if the screen is too bright. As described above, it is desired that the brightness of the screen, that is, the backlight, can be changed according to the brightness of the display environment.

A first conventional liquid crystal display device disclosed in Japanese Utility Model Laid-Open Publication No. Sho 63-60128, which is capable of dimming a backlight of this kind using a conventional fluorescent lamp, is a lamp for lighting a fluorescent lamp. The brightness of the lamp is adjusted by changing the duty ratio, which is the ratio between the pulse width of the rectangular wave and the period of this rectangular wave, to the constant current DC current waveform supplied to the booster circuit by varying the pulse width or the period. . Referring to FIG. 3, which shows a block diagram of a first conventional light control device, this conventional liquid crystal display device includes a DC power supply 11 and a DC current from the DC power supply 11 intermittently controlled by a light control signal C. A dimming unit 6 that generates a rectangular wave current with a variable duty ratio; and a voltage of the adjusted rectangular wave current supplied from the dimming unit 6 is boosted to a predetermined voltage level at which the lamp 4 can be turned on. And a step-up unit 3 including a transformer to be changed and a fluorescent lamp 4.

Referring to FIG. 3, which shows a block diagram of a first conventional light control device, this conventional light control device has a DC power supply 11.
A dimming unit 6 for generating a rectangular wave current having a variable duty ratio by intermitting a DC current from the DC power supply 11 with a dimming control signal C; A booster unit 3 including a transformer for boosting the adjusted voltage of the rectangular wave current to a predetermined voltage level at which the lamp 4 can be turned on, and a fluorescent lamp 4 are provided.

The dimming unit 6 controls the duty ratio of the dimming signal G by changing the duty ratio of the dimming signal G in response to the supply of a dimming control signal C from the outside. It includes a duty control unit 62 that generates the signal D, and a switch circuit 63 that interrupts the DC current supplied from the DC power supply 11 in response to the supply of the duty control signal D.

In operation, the dimming signal generator 61 supplies a dimming signal G, which is a DC voltage signal of a constant voltage, to the duty controller 62. The duty control section 62 controls the duty ratio of the dimming signal G by controlling the dimming control signal C, generates a duty control signal D, and supplies the generated signal to the switch circuit 63. The switch circuit 63 interrupts the constant-current DC current V supplied from the DC power supply in response to the supply of the duty control signal D,
A rectangular wave current E whose duty ratio is adjusted is generated and supplied to the booster 3. The booster 3 boosts the rectangular wave current E to a predetermined voltage and supplies the same to the lamp 4. When the voltage of the square wave current E is constant, the effective current supplied to the lamp 4, that is, the discharge current is proportional to the duty ratio, and the brightness of the lamp 4 is proportional to the discharge current. Is varied, the brightness of the lamp 4 can be varied.

As a result, the lamp is dimmed by fixing the voltage and adjusting only the duty ratio. However, it is generally difficult for the boosting transformer of the boosting unit 3 to increase the pass frequency bandwidth, and low loss is guaranteed at about 50% of the design center frequency. Therefore, when the duty ratio is extremely reduced, the pulse width of the rectangular wave signal is reduced, the high frequency component is increased, and the loss of the transformer of the booster 3 is increased. Therefore, the practical light control range is about 100 to 50%.

A second conventional liquid crystal display device described in Japanese Patent Application Laid-Open No. Sho 62-159137 is a voltage-controlled oscillation circuit in which the oscillation frequency or duty ratio of an oscillation signal is voltage-controlled by a dimming control signal, and a voltage-controlled oscillation circuit. And a phase control circuit for controlling the phase of the output control signal in accordance with the duty ratio, and varying the frequency or duty ratio to vary the phase of the output control signal, thereby connecting a triac connected to a commercial AC power supply for driving the lamp. By controlling the phase of the gate signal of the AC switch element, the effective supply voltage is varied to adjust the brightness of the lamp. Therefore, as is well known, not only the luminance but also the emission spectrum characteristics of the lamp change.

In addition, since the dimming is performed by varying the supply voltage of the lamp by controlling the phase of the commercial alternating current, the lower limit is up to the lower limit of the discharge voltage of the lamp.
It is about 0 to 50% or less.

[0010]

SUMMARY OF THE INVENTION The above-mentioned first prior art
The liquid crystal display device generates a rectangular wave current having the same waveform as the rectangular wave signal by directly switching a high-power DC power supply for driving the lamp with a rectangular wave signal having a variable duty ratio by pulse width or period control. Therefore, it is difficult to increase the speed of the switch circuit, and therefore, the frequency of the rectangular wave current cannot be increased sufficiently, which is a hindrance to downsizing the booster circuit and improving the luminous efficiency of the lamp. was there.

In the second conventional liquid crystal display device, a high-power commercial AC power source for driving a lamp is switched by phase control, so that it is difficult to increase the speed of a required high-voltage AC switch circuit. There is a drawback that it becomes a hindrance factor for improving the luminous efficiency of the lamp. Further, since the luminance of the lamp is voltage-controlled, there is a disadvantage that the emission spectrum characteristic changes.

Further, in both the first and second conventional liquid crystal display devices, the dimming range by varying the duty ratio or the phase is about 100 to 50%. There is a drawback that it is difficult.

[0013]

Means for Solving the Problems] light control device of the present invention is one
A transmitting circuit for supplying an alternating current having a constant frequency, and a pulse shape having a variable pulse width and a pulse period in which the alternating current is intermittently transmitted and received in response to the supply of a dimming signal generated in response to the supply of a dimming control signal A dimming circuit that generates a pulse-modulated alternating current that is an alternating current of a voltage, a booster circuit that generates a lamp driving current by boosting the voltage of the pulse-modulated alternating current to a predetermined voltage, and responds to the supply of the lamp driving current. A dimming device, comprising: a dimming circuit that illuminates the first and second lamps in response to the supply of the dimming control signal.
A dimming control unit for generating a control signal of
A dimming signal generation circuit that generates a pulse signal whose pulse period changes in response to the supply of the control signal, and a pulse width that changes in response to the supply of the second control signal and is synchronized with the pulse signal And a duty control unit for generating the dimming signal.

[0014]

FIG. 1 is a block diagram showing an embodiment of the present invention.
Referring to FIG. 1, the liquid crystal display device of this embodiment shown in FIG.
The dimming circuit is characterized by an oscillation circuit section 1 that generates an alternating current A having a constant frequency, and an intermittent alternating current A in response to a dimming signal D generated in response to a dimming control signal C. A dimming unit 2 for generating a pulse-like pulse-modulated alternating current E having a variable pulse width and a pulse period; and a conventional dimming unit for raising the voltage of the pulse-modulated alternating current E to a predetermined voltage level at which the lamp 4 can be turned on A booster 3 and a fluorescent lamp 4 are provided.

The dimming section 2 responds to the supply of the dimming control signal C with the cycle control signal CP and the duty control signal C.
D, a dimming signal generator 21 that generates a pulse signal P whose pulse cycle is controlled in response to the supply of the cycle control signal CP, and a dimmer control signal CD that responds to the supply of the duty control signal CD. And a duty control unit 22 for controlling the pulse width and generating a dimming signal D synchronized with the pulse signal P. And a switch circuit 23 for generating.

Next, the operation of the present embodiment will be described with reference to FIG. 1. First, the dimming control unit 24 responds to the supply of the dimming control signal C by using a period control signal CP which is a voltage signal. And a duty control signal CD. The dimming signal generation unit 21 includes a variable pulse period type pulse oscillation circuit constituted by a voltage controlled oscillation circuit (VCO) using a well-known astable multivibrator, and the pulse period is adjusted in response to the supply of the period control signal CP. A pulse signal P is generated and supplied to the duty control unit 22. The duty control unit 22 includes a well-known monostable multivibrator triggered by the pulse signal P, and controls the pulse width of the output pulse signal, that is, the dimming signal D, that is, the duty ratio in response to the supply of the duty control signal CD. An optical signal D is generated and supplied to the switch circuit 23. The switch circuit 23 interrupts the AC current A in response to the supply of the dimming signal D, generates a pulse-modulated AC current E, and supplies the pulse-modulated AC current E to the booster 3. The booster 3 boosts the pulse-modulated AC current E to a predetermined voltage and supplies the same to the lamp 4.

Referring to FIG. 2 showing operation waveforms of this embodiment, when the duty ratio of the dimming signal D is 100%,
As shown in (A), since the switch circuit 23 is always in the conductive state, the AC current A is directly used as the pulse-modulated AC current E.
Is output as Next, if the duty ratio is set to 50% by reducing the pulse width of the dimming signal D, the pulse period T becomes twice the pulse width as shown in FIG. Further, as shown in (C), if the period is increased to T2 while the pulse width of the dimming signal D is kept constant, the duty ratio becomes 50
% Or less, and the brightness of the lamp 4 can be further reduced to light the lamp.

[0018]

As described above, according to the present invention, the light control device of the present invention includes a transmission circuit section, the alternating current in response to the supply of the dimming control signal dimming signal generated in response to the supply of intermittent A dimming circuit that generates a pulse-modulated alternating current having a variable pulse width and a pulse period, wherein the dimming circuit generates a dimming signal that changes the pulse period; and the pulse width changes. And a duty control unit that generates the dimming signal synchronized with the pulse signal, thereby pulse-modulating the alternating current, changing the pulse width and the pulse period, and changing the duty ratio. The operating center frequency of the transformer is the frequency of the AC current, and the ratio band is independent of the duty ratio. Therefore, the transformer can be operated with high efficiency. There is an effect that high efficiency miniaturization of road becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a dimming circuit characterizing a liquid crystal display device of the present invention.

FIG. 2 is a waveform chart showing an example of the operation of the dimming circuit of the present embodiment.

FIG. 3 is a block diagram illustrating an example of a dimming circuit of a conventional liquid crystal display device.

Claims (3)

(57) [Claims] 1. A transmission type liquid crystal display panel, a transmission circuit section for supplying an alternating current of a fixed frequency, and said alternating current in response to a supply of a dimming signal generated in response to a supply of a dimming control signal. A dimming unit that generates a pulse-modulated alternating current that is a pulse-shaped alternating current with a variable pulse width and a pulse period by intermittently supplying a current, and generates a lamp driving current by boosting the voltage of the pulse-modulated alternating current to a predetermined voltage In a liquid crystal display device including a booster circuit section and a fluorescent lamp type lamp arranged on the back surface of the liquid crystal panel and turned on in response to the supply of the lamp drive current, the dimming section includes A dimming control circuit for generating first and second control signals in response to the supply, and a dimming signal generating circuit for generating a pulse signal in which the pulse period changes in response to the supply of the first control signal And before The liquid crystal display device, characterized in that it comprises a de-utility control circuit for generating the dimming signal synchronized with the pulse signal with a pulse width in response to the supply of the second control signal changes. 2. The liquid crystal display device according to claim 1, wherein the dimming signal generation circuit includes a voltage controlled oscillation circuit including an astable multivibrator. 3. The liquid crystal display device according to claim 1, wherein the duty control circuit includes a monostable multivibrator triggered by the pulse signal.