JPH07183092A - Dimmer - Google Patents

Abstract

PURPOSE:To enlarge the dimming range of the backlight of a liquid crystal display device. CONSTITUTION:A dimmer has an oscillating circuit portion 1 for generating alternating current A and a dimming portion 2 which interrupts the alternating current A in response to the supply of a dimming signal D generated by a dimming control signal C, to produce a pulse-modulated alternating current E of a variable pulse width and period. The dimming portion 2 includes a dimming control portion 24 which generates a period control signal CP and a duty control signal CD in response to the supply of the dimming control signal C; a dimming-signal generating portion 21 which generates pulse signals P whose pulse period is controlled by the period control signal CP; a duty cycle control portion 22 which controls the pulse width according to the duty cycle control signal CD and generates a dimming signal D synchronous with the pulse signal P; and a switching circuit 23 which interrupts the alternating current A according to the dimming signal D to generate a pulse-modulated alternating current E.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control device, and more particularly to a light control device for a backlight of a transmissive liquid crystal display device.

[0002]

2. Description of the Related Art Since a liquid crystal display (LCD) is a non-emissive display, it is necessary to illuminate it in a place where external light conditions are poor. Especially, a transmission type L used for liquid crystal televisions and OA terminals.
The CD is equipped with a surface light source, that is, a backlight for uniformly illuminating the LCD surface from the rear side in order to perform a clear display. A fluorescent lamp is mainly used as a light source of this backlight. The image displayed on the LCD is displayed by the light from 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 periphery of the display is bright, it is difficult to see unless the screen is bright, while when the periphery is dark, it becomes 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 light control device disclosed in Japanese Utility Model Laid-Open No. 63-60128, which enables light control of a backlight of this type using a conventional fluorescent light, is for lighting a lamp which is a fluorescent light. The brightness of the lamp is adjusted by changing the duty ratio, which is the ratio of the DC current waveform of a constant voltage supplied to the booster circuit, that is, the pulse width of the rectangular wave to the period of the rectangular wave, by changing the pulse width or the period. .

Referring to FIG. 3, which shows a block diagram of a first conventional dimmer, this conventional dimmer is a direct current power supply 11
Of the duty ratio supplied from the dimming unit 6, and a dimming unit 6 that generates a rectangular wave current in which the DC current from the DC power supply 11 is intermittently changed by the dimming control signal C to change the duty ratio of the current. The fluorescent lamp lamp 4 is provided with a booster unit 3 including a transformer that boosts the voltage of the adjusted rectangular wave current to a predetermined voltage level at which the lamp 4 can be turned on.

The dimming unit 6 changes the duty ratio of the dimming signal G in response to the supply of the dimming signal generating unit 61 for generating the dimming signal G and the dimming control signal C from the outside. The duty control unit 62 that generates the signal D and the switch circuit 63 that connects and disconnects the DC current supplied from the DC power supply 11 in response to the supply of the duty control signal D are provided.

To explain the 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 unit 62 controls the duty ratio of the dimming signal G by controlling the dimming control signal C, generates the duty control signal D, and supplies it to the switch circuit 63. The switch circuit 63 responds to the supply of the duty control signal D to interrupt the DC current V of a constant voltage supplied from the DC power supply,
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 it to the lamp 4. When the voltage of the rectangular 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. The brightness of the lamp 4 can be changed by changing the.

As a result, the lamp is dimmed by fixing the voltage and adjusting only the duty ratio. However, in the step-up transformer of the step-up unit 3, it is generally difficult to increase the pass frequency bandwidth, and low loss is guaranteed only about 50% with respect to the design center frequency. Therefore, if the duty ratio is extremely reduced, the pulse width of the rectangular wave signal becomes smaller, the high frequency component increases, and the loss of the transformer of the booster 3 increases, so that the lighting state of the lamp becomes unstable and finally the lamp does not light. Therefore, the practical dimming range is about 100 to 50%.

The second conventional dimmer disclosed in Japanese Patent Laid-Open No. 62-159137 discloses a voltage controlled oscillator circuit in which the oscillation frequency or duty ratio of an oscillation signal is voltage controlled by a dimming control signal, and these frequencies. A phase control circuit that controls the phase of the output control signal by the duty ratio, and the frequency or duty ratio is changed to change the phase of the output control signal, and a triac connected to a commercial AC power supply for lamp drive, etc. By controlling the phase of the gate signal of the AC switch element, the effective supply voltage is varied and the brightness of the lamp is adjusted. Therefore, as is well known, not only the luminance but also the emission spectrum characteristic of the lamp changes.

Further, since the dimming is performed by changing the voltage supplied to the lamp by controlling the phase of the commercial AC, the lower limit is up to the lower limit of the discharge voltage of the lamp, and the practical dimming range is 10.
It is about 0 to 50% or less.

[0010]

SUMMARY OF THE INVENTION In the first conventional light control device described above, a high-power DC power source for driving a lamp is directly switched by a rectangular wave signal having a variable duty ratio by pulse width or cycle control. Since the rectangular wave current having the same waveform as this rectangular wave signal is generated, it is difficult to increase the speed of the switch circuit. Therefore, the frequency of the rectangular wave current cannot be increased sufficiently, and the booster circuit is downsized. There is a drawback that it becomes a factor that hinders improvement of efficiency and improvement of luminous efficiency of the lamp.

In the second conventional light control device, the high-power commercial AC power source for driving the lamp is switched by the phase control, so that it is difficult to speed up the required high-voltage AC switch circuit. However, there is a drawback that it becomes an obstacle to improving the luminous efficiency of the lamp. Further, since the luminance of the lamp is voltage-controlled, there is a drawback that the emission spectrum characteristic changes.

Further, both the first and second conventional dimming devices have a dimming range of about 100 to 50% by varying the duty ratio or the phase, and it is difficult to widen this dimming range. There was a drawback.

[0013]

SUMMARY OF THE INVENTION The dimming device of the present invention provides an alternating current source for supplying an alternating current having a predetermined frequency and a dimming signal generated in response to the supply of a dimming control signal. A dimmer circuit that responds by intermittently generating the pulse-modulated AC current that is a pulse-shaped AC current having a variable pulse width and a pulse period, and a lamp that boosts the voltage of the pulse-modulated AC current to a predetermined voltage. In a dimming device including a booster circuit that generates a driving current and a fluorescent lamp type lamp that lights up in response to the supply of the lamp driving current, the dimming circuit responds to the supply of the dimming control signal. A dimming control unit that generates first and second control signals; a dimming signal generation circuit that generates a pulse signal whose pulse period changes in response to the supply of the first control signal;
And a duty control section for changing the pulse width in response to the supply of the control signal and for generating the dimming signal synchronized with the pulse signal.

[0014]

1 is a block diagram showing an embodiment of the present invention.
Referring to FIG. 2, the dimming device of the present embodiment shown in this figure has an oscillation circuit section 1 that generates an alternating current A having a constant frequency and a dimming signal D that is generated in response to the supply of a dimming control signal C. In response to the supply, this alternating current A is intermittently turned on and off, and a pulse-shaped pulse-modulated alternating current E having a variable pulse width and pulse period
And a booster 3 similar to the conventional one that boosts the voltage of the pulse-modulated AC current E to a predetermined voltage level at which the lamp 4 can be turned on, and a fluorescent lamp 4.

The dimming section 2 is responsive to the supply of the dimming control signal C to control the period control signal CP and the duty control signal C.
A dimming control section 24 for generating D, a dimming signal generating section 21 for generating a pulse signal P whose pulse cycle is controlled in response to the supply of the cycle control signal CP, and a supply of a duty control signal CD. To control the pulse width and to generate a dimming signal D synchronized with the pulse signal P, and in response to the supply of the dimming signal D, the alternating current A is intermittently switched to generate the pulse modulated alternating current E. And a switch circuit 23 for generating.

Next, the operation of this embodiment will be described with reference to FIG. 1. First, the dimming control section 24 responds to the supply of the dimming control signal C, and the period control signal CP, which is a voltage signal, respectively. And a duty control signal CD. The dimming signal generator 21 includes a pulse oscillation circuit of a variable pulse period type configured 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. The generated pulse signal P is generated and supplied to the duty control unit 22. The duty control unit 22 includes a well-known monostable multivibrator that is triggered by the pulse signal P, and controls the pulse width, that is, the duty ratio of the output pulse signal, that is, the dimming signal D in response to the supply of the duty control signal CD. The optical signal D is generated and supplied to the switch circuit 23. In response to the supply of the dimming signal D, the switch circuit 23 interrupts the alternating current A to generate the pulse-modulated alternating current E and supplies it to the booster 3. The booster 3 boosts the pulse-modulated AC current E to a predetermined voltage and supplies it to the lamp 4.

Referring to FIG. 2 showing the 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 the pulse-modulated AC current E as it is.
Is output as. Next, when the pulse width of the dimming signal D is reduced and the duty ratio is set to 50%, the pulse period T becomes twice the pulse width as shown in (B). Further, as shown in (C), when the period is increased to T2 while keeping the pulse width of the dimming signal D constant, the duty ratio becomes 50.
% Or less, and the brightness of the lamp 4 can be further lowered to enable lighting.

[0018]

As described above, the dimmer of the present invention intermittently switches the alternating current in response to the alternating current source and the supply of the dimming signal generated in response to the supply of the dimming control signal. And a dimming circuit that generates a pulse-modulated alternating current with a variable pulse width and a pulse period, the dimming circuit generating a pulse signal with the pulse period varying, and the pulse width varying. A duty control unit that generates the dimming signal synchronized with the pulse signal is provided, and the duty ratio is changed by pulse-modulating the alternating current to change the pulse width and the pulse period. The operating center frequency of the transformer is the frequency of the AC current above, and since the ratio band is independent of the duty ratio, it can be operated with high efficiency. There is an effect that high efficiency miniaturization of road becomes possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a light control device of the present invention.

FIG. 2 is a waveform diagram showing an example of an operation in the light control device of the present embodiment.

FIG. 3 is a block diagram showing an example of a conventional light control device.

[Explanation of symbols]

 1 Oscillation circuit section 2,6 Dimming section 3 Boosting section 4 Lamp 11 DC power supply 21,61 Dimming signal generating section 22,62 Duty control section 23,63 Switch circuit 24 Dimming control section

Claims (3)

[Claims] 1. An alternating current source for supplying an alternating current of a predetermined frequency, and a variable pulse width for intermittently interrupting the alternating current in response to the supply of a dimming signal generated in response to the supply of a dimming control signal. And a dimming circuit that generates a pulse-modulated AC current that is a pulse-shaped AC current having a pulse period, a booster circuit that boosts the voltage of the pulse-modulated AC current to a predetermined voltage to generate a lamp drive current, and the lamp drive In a dimmer including a fluorescent lamp that lights up in response to the supply of an electric current, the dimming circuit responds to the supply of the dimming control signal to the first dimming circuit.
And a dimming control circuit that generates a second control signal, a dimming signal generation circuit that generates a pulse signal whose pulse period changes in response to the supply of the first control signal, and the second control And a duty control circuit that changes the pulse width in response to the supply of a signal and generates the dimming signal synchronized with the pulse signal. 2. The dimming device according to claim 1, wherein the dimming signal generating circuit comprises a voltage controlled oscillator circuit including an astable multivibrator. 3. The dimmer according to claim 1, wherein the duty control circuit comprises a monostable multivibrator triggered by the pulse signal.