KR100594889B1 - Dimming circuit of inverter - Google Patents

Abstract

The present invention relates to a dimming circuit of an inverter, and more particularly, in the dimming circuit, the operation of the first comparator is controlled according to the magnitude of the dimming input voltage to perform a line dimming operation when the dimming input voltage is lower than a predetermined voltage. It solves the flicker phenomenon caused by the frequency interference when it is bright and performs the burst dimming operation when the dimming input voltage is above a certain voltage. Can be improved.

Inverter, cold cathode tube, dimming, burst, linear

Description

Dimming circuit of inverter {DIMMING CIRCUIT OF INVERTER}

1 is a block circuit diagram schematically showing a configuration of a conventional inverter

2 is a block circuit diagram showing a state in which the dimming circuit of the inverter according to the present invention is applied to the inverter

<Description of the symbols for the main parts of the drawings>

10: Inverter 11: PWM control circuit

15: cold cathode tube 17: detection circuit

19: adder 100: dimming circuit

110: linear dimming circuit 120: triangle wave generator circuit

130: first comparator 140: second comparator

150: power switching circuit

The present invention relates to an inverter, and more particularly, a dimming circuit of an inverter to prevent occurrence of luminance ratio and frequency interference by using a burst dimming method and a linear dimming method in common. It is about.

In general, the inverter refers to a circuit that lights up the backlight of the TFT LCD panel and stabilizes the lighting of the backlight.

As shown in FIG. 1, the conventional inverter 10 includes a PWM control circuit 11, a switching circuit 12, an oscillation circuit 13, a boost transformer 14, and a cold cathode tube 15. ), A protection circuit 16, a detection circuit 17, a dimming circuit 18, and an adder 19.

The PWM control circuit 11 outputs a control signal fixedly fixed to a change in input voltage variation from the outside in accordance with the input signal, and the switching circuit 12 is connected to the control signal output from the PWM control circuit 11. And switch and accumulate and discharge the switched signals.

The oscillation circuit 13 outputs an oscillation signal according to the switching of the switching circuit 12, the boosting transformer 14 boosts and outputs the signal output from the oscillation circuit 13, and the cold cathode tube 15 boosts the voltage. The lamp is turned on in accordance with the signal output from the transformer 14.

The protection circuit 16 senses a signal output through the cold cathode tube 15 and outputs a control signal to the PWM control circuit 11 when the signal output through the cold cathode tube 15 is above a predetermined level. 15) Turn off the lighting.

The detection circuit 17 senses a signal output through the cold cathode tube 15, feeds back a signal level, and the dimming circuit 18 receives the cold cathode tube 15 according to a dimming input voltage input under a user's control. Outputs a dimming signal to adjust the brightness of the

The adder 19 adds the signals output from the detection circuit 17 and the dimming circuit 18 and outputs them to the PWM control circuit 11.

The operation of the conventional inverter will be described in detail with reference to FIG. 1 as follows.

When the input voltage is input to the PWM control circuit 11 to drive the inverter 10, the PWM control circuit 11 outputs a control signal to the switching circuit 12 and switches the oscillation signal from the oscillation circuit 13. Be sure to

When the oscillation signal is output from the oscillation circuit 13, the boosting transformer 14 boosts it and outputs it to the cold cathode tube 15 so that the cold cathode tube 15 is turned on. At this time, the protection circuit 16 senses a signal output through the cold cathode tube 15 and outputs a control signal to the PWM control circuit 11 when the signal output through the cold cathode tube 15 is above a predetermined level. The lighting of (15) is turned off.

Meanwhile, the detection circuit 17 senses a signal output through the cold cathode tube 15 to feed back a signal level, and the dimming circuit 18 receives the cold cathode tube 15 according to a dimming input voltage input under a user's control. When the dimming signal for adjusting the brightness of the output is added, the adder 19 adds the signals output from the detection circuit 17 and the dimming circuit 18 to the PWM control circuit 11 to output the brightness of the cold cathode tube 15. Adjust it. In this case, a linear dimming method of adjusting the brightness by changing the magnitude of the output voltage according to the dimming circuit 18 and a burst dimming method of controlling the brightness by intermittently turning the output on and off are used.

However, in the conventional dimming method of the inverter, when the magnitude of the output voltage is changed like the linear dimming method, the brightness adjustment of the brightness may not be apparent, and the brightness is adjusted by intermittently turning the output on and off like the burst dimming method. In this case, the brightness ratio can be adjusted, but there is a problem that frequency interference occurs.

Accordingly, an object of the present invention is to solve the above problems, by implementing a dimming circuit using a combination of the burst dimming and linear dimming method to block the occurrence of the luminance ratio and frequency interference phenomenon.

Features of the present invention for achieving the above object,

In an inverter including a PWM control circuit, a switching circuit, an oscillation circuit, a boost transformer, a cold cathode tube, a protection circuit, a detection circuit, a dimming circuit, and an adder,

The dimming circuit,

A linear dimming circuit for outputting a linear dimming voltage to the adder by dropping a dimming input voltage input from the outside by a predetermined level;

A triangle wave generator for outputting a triangle wave signal;

Any one input terminal is connected on the line connected to the linear dimming circuit and the adder, is connected to the other input terminal to the output side of the triangular wave generator circuit, the output terminal is connected to one end of the adder, and is input from the outside A first comparator operated according to a control signal and comparing the respective input signals and outputting a comparison value to the adder;

A dimming input terminal for outputting a dimming input voltage is connected to any one input terminal, the other input terminal is connected to the ground, an output terminal is connected to the control terminal of the first comparator, the size of the dimming input voltage input from the outside A second comparator for operating the first comparator by outputting a control signal to the first comparator when the dimming voltage is greater than the reference voltage compared to the reference voltage;

And a power switching circuit connected between an output terminal of the second comparator and a control terminal of the first comparator and switched according to an output signal of the second comparator to operate the first comparator.

Here, the power switching circuit,

A base is connected to the output terminal of the second comparator, an emitter is connected to the constant voltage terminal, and a collector is connected to the control terminal of the first comparator.

Hereinafter, the configuration of the dimming circuit of the inverter according to the present invention will be described in detail with reference to FIG. In FIG. 2, the same parts as those of the inverter shown in FIG. 1 are given the same reference numerals as in FIG. 1, and description thereof will be omitted.

2 is a block circuit diagram showing a state in which the dimming circuit of the inverter according to the present invention is applied to the inverter.

Referring to FIG. 2, the dimming circuit 100 of the inverter according to the present invention includes a linear dimming circuit 110, a triangular wave generator circuit 120, a first comparator 130, a second comparator 140, , The power switching circuit 150.

The linear dimming circuit 110 drops the dimming input voltage input from the outside by a predetermined level and outputs the linear dimming voltage to the adder 19 and the first comparator 130.

The triangular wave generating circuit 120 outputs a triangular wave signal.

The first comparator 130 is connected to any one input terminal on the line connected to the linear dimming circuit 110 and the adder 19, is connected to the other input terminal on the output side of the triangle wave generator circuit 120, the adder An output terminal is connected to one end of the terminal 19, and operated according to a control signal input from the outside to compare the respective input signals and output a comparison value to the adder 19.

The second comparator 140 is connected to one input terminal to a dimming input terminal for outputting a dimming input voltage, the other input terminal is connected to ground, and the output terminal is connected to a control terminal of the first comparator 130, When the dimming voltage is greater than the reference voltage by comparing the magnitude of the dimming input voltage input from the reference voltage, the control signal is output to the first comparator 130 to operate the first comparator 130.

The power switching circuit 150 is connected between the output terminal of the second comparator 140 and the control terminal of the first comparator 130 and switched according to the output signal of the second comparator 140 to operate the second comparator 140. Let's do it. Here, the power switching circuit has a base connected to the output terminal of the second comparator 140, an emitter connected to the constant voltage terminal Vcc, and a collector connected to the control terminal of the first comparator 130. When the signal is output from the transistor 140, the transistor is turned on to output the voltage of the constant voltage terminal Vcc to the first comparator 130 to operate the first comparator 130.

Hereinafter, the operation of the dimming circuit of the inverter according to the present invention will be described in detail with reference to FIG. 2.

First, when an input voltage is input to the PWM control circuit 11 to drive the inverter 10, the PWM control circuit 11 outputs a control signal to the switching circuit 12 and switches the oscillation signal from the oscillation circuit 13. To be printed.

When the oscillation signal is output from the oscillation circuit 13, the boosting transformer 14 boosts it and outputs it to the cold cathode tube 15 so that the cold cathode tube 15 is turned on. At this time, the protection circuit 16 senses a signal output through the cold cathode tube 15 and outputs a control signal to the PWM control circuit 11 when the signal output through the cold cathode tube 15 is above a predetermined level. The lighting of (15) is turned off.

The detection circuit 17 senses a signal output through the cold cathode tube 15 and feeds back a signal level.

Meanwhile, when the dimming input voltage is applied, the second comparator 140 of the dimming circuit 100 compares the dimming input voltage with the reference voltage and turns on the power switching circuit 150 when the dimming input voltage is greater than the reference voltage. When the power switching circuit 150 is turned on and power is supplied to the first comparator 130, the first comparator 130 compares the output signals of the linear dimming circuit 110 and the triangular wave generator circuit 120 to make a difference. The signal is output to the adder 19 in accordance with this.

Then, when the adder 19 sums the respective output signals of the linear dimming circuit 110, the first comparator 130, and the detection circuit 17 and outputs them to the PWM control circuit 11, the PWM control circuit 11 performs PWM modulation. The square wave is turned on / off the feedback signal to perform a burst dimming operation.

In addition, when the dimming input voltage is less than the reference voltage of the second comparator 140, the second comparator 140 is turned off or maintains a turn-off state. Then, since the first comparator 130 is also not operated, only the output signals of the linear dimming circuit 110 and the detection circuit 17 are input to the adder 19.

Then, when the adder 19 sums the respective output signals of the linear dimming circuit 110 and the detection circuit 17 and outputs them to the PWM control circuit 11, the PWM control circuit 11 changes the magnitude of the output voltage to linear dimming. Perform the action.

Therefore, the dimming circuit controls the operation of the first comparator according to the size of the dimming input voltage and performs a linear dimming operation when the dimming input voltage is lower than a predetermined voltage to prevent flicker caused by frequency interference when the cold cathode tube is bright. When the dimming input voltage is above a certain voltage, the burst dimming operation is performed to improve the luminance ratio by darkening the cold cathode tube after darkening the cold cathode tube to some extent.

As described above, according to the dimming circuit of the inverter according to the present invention, a dimming circuit using a burst dimming scheme and a linear dimming scheme may be implemented to prevent occurrence of luminance ratio and frequency interference.

Claims (2)

In an inverter including a PWM control circuit, a switching circuit, an oscillation circuit, a boost transformer, a cold cathode tube, a protection circuit, a detection circuit, a dimming circuit, and an adder, The dimming circuit, A linear dimming circuit for outputting a linear dimming voltage to the adder by dropping a dimming input voltage input from the outside by a predetermined level; A triangle wave generator for outputting a triangle wave signal; Any one input terminal is connected on the line connected to the linear dimming circuit and the adder, is connected to the other input terminal to the output side of the triangular wave generator circuit, the output terminal is connected to one end of the adder, and is input from the outside A first comparator operated according to a control signal and comparing the respective input signals and outputting a comparison value to the adder; A dimming input terminal for outputting a dimming input voltage is connected to any one input terminal, the other input terminal is connected to the ground, an output terminal is connected to the control terminal of the first comparator, the size of the dimming input voltage input from the outside A second comparator for operating the first comparator by outputting a control signal to the first comparator when the dimming voltage is greater than the reference voltage compared to the reference voltage; A dimming circuit of an inverter connected between an output terminal of the second comparator and a control terminal of the first comparator and switched according to an output signal of the second comparator to operate the first comparator . The method of claim 1, The power supply switching circuit, And a transistor having a base connected to an output terminal of the second comparator, an emitter connected to a constant voltage terminal, and a collector connected to a control terminal of the first comparator.

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