JPH0827451B2 - Light control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dimming device for dimming a cold cathode discharge tube by using a frame signal of the liquid crystal display device for illumination of the liquid crystal display device.

2. Description of the Related Art A conventional light control device will be described. FIG. 3 is a circuit diagram of a conventional dimmer, 1 is a DC power supply, 2 is a DC-AC converter for applying a high-voltage AC voltage to the cold cathode discharge tube 3, and 4 is an input voltage of the DC-AC converter 2. A transistor that controls
7 is a voltage control IC for controlling by comparing the resistances 8 and 10 for detecting the output voltage of the transistor 4 with the voltage detected by the dimming variable resistor 9, and 6 is a base current of the transistor 4 Resistor, 5 is a resistor, and 11 is a capacitor.

The operation of the light control device configured as described above will be described below.

The voltage of the DC power supply 1 is input to the emitter of the voltage control transistor 4, and a stabilized voltage lower than that of the DC power supply 1 is output from the collector. The stabilized output voltage of the collector is controlled by the variable voltage control IC 7 and the partial voltage created by the output voltage detection resistors 8 and 10 and the dimming variable resistor 9. Therefore, by varying the resistance value of the dimming variable resistor 9, the collector voltage of the voltage control voltage transistor 4 is controlled. The resistor 6 limits the base current of the voltage controlling transistor 4. The capacitor 11 stabilizes the collector voltage of the transistor 4. Next, when the collector voltage of the voltage control transistor 4 changes, the input voltage of the DC-AC converter 2 changes and the output voltage of the DC-AC converter 2 changes, so the current flowing through the cold cathode discharge tube 3 changes. , The brightness of the cold cathode discharge tube 3 changes.

However, since the output of the DC-AC converter 2 is changed in the above conventional configuration, in order to light the cold cathode discharge tube 3 even at a low temperature of 0 ° C. or less, the discharge tube There was a problem that the brightness could only be reduced by 50% at the maximum.

The present invention solves the above-mentioned conventional problems, and can reduce the brightness of the discharge tube to about 10%, and the interference difference due to the lighting of the cold cathode discharge tube and the brightness difference due to the scanning of the liquid crystal display device. It is an object of the present invention to provide a light control device that can make the light inconspicuous.

Means for Solving the Problems In order to solve this object, a dimmer of the present invention is a multiplier that produces an integer multiple signal synchronized with a frame signal of a liquid crystal display device, and a resistor that produces a pseudo triangular wave from the signal. , A capacitor, a resistor for producing a dimming reference voltage, a variable resistor, a comparator for comparing the dimming reference voltage with a pseudo triangular wave, a transistor for switching a DC power supply based on the signal of the comparator, and a DC-AC converter It consists of

Operation With this configuration, the brightness of the cold cathode discharge tube can be reduced to about 10% even at a low temperature of 0 ° C. or less, and interference fringes with the liquid crystal display device can be made inconspicuous.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of a dimmer in one embodiment of the present invention.

In FIG. 1, reference numeral 26 is a multiplication circuit for producing an integral multiple signal synchronized with the frame signal of the liquid crystal display device, 13, 14 are resistors and capacitors for producing a pseudo triangular wave from the output of the multiplication circuit 26, 17 is a variable resistor for dimming, 16, 18 is a resistor that creates a dimming reference voltage, 19 is a capacitor that removes noise from the dimming reference voltage, 15 is a comparator that compares the pseudo triangular wave with the dimming reference voltage, and 20 is a pull for the output of the compacolator 15. Up resistor, 22 is a control transistor for controlling the base current of the switching transistor 25 by inputting the output of the comparator 15, 23 is a resistor for limiting the base current of the switching transistor 25, and 21 and 24 are transistors 22 and 25, respectively.
It is a resistor for stable operation. 1, 2, and 3 have the same configuration as the conventional example. Reference numeral 12 is a DC power supply for the comparator 15. 27 is an input terminal to which a frame signal is input.

The operation of the light control device configured as described above will be described below.

The frame signal of the liquid crystal display is input from terminal 27, and the multiplier 26 synchronizes the frame signal with an integer multiple and duty 50.
Produces a% signal. Resistor 13 and capacitor from that signal
14 creates a pseudo triangular wave. On the other hand, the dimming variable resistor 17 and the resistors 16 and 18 generate a dimming reference voltage.
The dimming reference voltage and the pseudo triangular wave are input to the comparator 15 for comparison.

When the voltage of the pseudo triangular wave is lower than the reference voltage for dimming, the output of the comparator 15 is in the open state and the control transistor 22 is operated through the resistor 20. At this time, the collector-emitter of the control transistor 22 becomes conductive, the switching transistor 25 is operated through the resistor 23, and the collector-emitter becomes conductive.

If the voltage of the pseudo triangle wave is higher than the reference voltage for dimming,
The output of the comparator 15 is short-circuited to the ground of the power supply voltage, the control transistor 22 does not operate, the collector-emitter is non-conductive, the switching transistor 25 does not operate, and the collector-commiter is non-conductive. It becomes a state.

By the above operation, the input voltage of the DC-AC conversion 2 is N and FF in a state of being synchronized with the frame signal of the liquid crystal display device. Since the input voltage of the DC-AC converter 2 is N, FF, the DC / AC voltage is similarly N, FF, and the current flowing through the cold cathode discharge tube 3 is controlled by time. Even if the time during which the input voltage of the DC-AC converter 2 is N is shortened, the peak value of the output voltage of the DC-AC converter 2 does not change, so the cold cathode discharge tube 3 does not go out. .

FIG. 2 shows the waveform relationship of the frame signal of the liquid crystal display device, the output of the multiplier 26, the pseudo triangular wave, the reference voltage for dimming, and the input voltage of the DC / AC converter 2 when the multiplier 26 is 5 times.

As described above, according to the present embodiment, the pseudo triangular wave synchronized with the frame signal of the liquid crystal display device is compared with the reference voltage for dimming, and the switching transistor 25 is controlled by N and FF, thereby performing cold cathode discharge. The brightness of the tube 3 can be dimmed. Furthermore, if the frame signal of the liquid crystal display device and the N, FF operation of the DC-AC converter 2 are not synchronized,
Since interference fringes appear as if they flow on the display device because they are out of phase with the frame signal of the liquid crystal display device, this configuration causes a difficult phenomenon. Since the FF operation is synchronized, the interference fringe can be made inconspicuous.

In FIG. 2 showing the timing chart for explaining the operation of the present embodiment, the multiplier 26 has a multiplication factor of 5. However, the multiplication factor of the multiplier is an integral multiple in which interference fringes with the liquid crystal display device are inconspicuous. But it's okay.

EFFECTS OF THE INVENTION The present invention can perform dimming of a cold cathode discharge tube by comparing a pseudo triangular wave and a dimming reference voltage and turning on / off an input voltage of a DC-AC converter by a switching transistor. In addition, by turning on and off the input voltage of the DC-AC converter in synchronization with an integral multiple of the frame signal period of the liquid crystal display device, the brightness difference due to lighting and turning off of the cold cathode discharge tube and the liquid crystal display device Interference fringes caused by scanning appear to stop on the screen of the liquid crystal display device.
If the lighting / extinguishing cycle is the same as the frame signal cycle, the intensity of the interference stripes will be coordinated, but by setting the lighting / extinguishing cycle to be an integral multiple of the frame signal cycle, the intensity of the interference stripes will change from the afterglow characteristics of the discharge tube. It is possible to realize an excellent dimming device that can obtain the effect of making the interference weak and making the interference fringes inconspicuous.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a dimmer in one embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of a tuning light device, and FIG. 3 is a circuit diagram of a conventional dimmer. 1 ... DC power supply, 2 ... DC-AC converter, 3 ... cold cathode discharge tube, 12 ... DC power supply, 13 ... resistance, 14 ... condenser, 15 ... comparator, 16 ... resistance, 17 ...... Variable resistor for dimming, 18 ...... Resistor, 19 ...... Capacitor, 20, 21 ......
Resistance, 22 …… Control transistor, 23,24 …… Resistance, 25
...... Switching transistor, 26 …… Multiplier.

Claims (1)

[Claims] 1. A multiplier that outputs an integer multiple signal synchronized with a frame signal of a liquid crystal display device, a resistor and a capacitor that generate a pseudo triangular wave signal from the output signal of the multiplier, and at least a variable resistor. A dimming reference voltage is applied to one input terminal, and a comparator to which the pseudo triangular wave signal is applied to the other input terminal is provided.
A dimming device characterized in that an input voltage of a DC-AC converter for a cold cathode discharge tube is turned on and off by using an output signal of this comparator.