KR19990028849U - Monitor automatic brightness adjustment circuit - Google Patents

Abstract

The present invention automatically changes the contrast of the screen as the ABL voltage output from the ABL terminal of the flyback transformer 30 changes, and also changes the brightness of the screen, thereby automatically changing the brightness and sharpness of the screen. A circuit for automatically adjusting the brightness of a monitor to be adjusted.

According to the present invention, when the user adjusts the contrast of the screen, as the anode current is displayed above the threshold value, when the ABL voltage output from the flyback transformer 30 decreases, the zener diode ZD1 and the transistor Q3 of the brightness control unit 23 are reduced. When the ABL voltage output from the flyback transformer 30 is increased by turning off the brightness control signal outputted from the microcomputer 10 to the DC bias control unit 22 so as not to be variable, and the anode current is within a threshold value. Zener diode ZD1 and transistor Q3 of the brightness control unit 23 are turned on to reduce the brightness of the brightness control signal output from the microcomputer 10 and input to the DC bias control unit 22, thereby changing the brightness of the screen. The brightness and sharpness of the screen are automatically adjusted.

Description

Automatic brightness limiter of a monitor

The present invention relates to an automatic brightness limiter (ABL) for adjusting the brightness and contrast of a monitor.

In general, the automatic brightness control circuit (ABL) of the monitor is a circuit that automatically adjusts the brightness of the screen displayed on the receiving tube by the brightness control signal and the contrast control signal output from the microcomputer. As the screen becomes abnormally bright, the receiving tube If the anode current exceeds the threshold, the screen has the function of reducing the brightness of the screen by limiting the anode current to prevent overload of the high voltage generator circuit and the destruction of the components.

FIG. 1 is a diagram illustrating the automatic brightness control circuit as described above, and includes a microcomputer 10, a video preamplifier 20, a video power amplifier 21, a DC bias controller 22, a flyback transformer 30, and the like. , Contrast control unit 40, in particular, the contrast control unit 40 outputs a low emitter voltage as the current flowing into the ABL terminal of the flyback transformer 30 increases the magnitude of the contrast control signal When the first transistor Q1 and the first transistor Q1 are reduced, they are turned on together to reduce the magnitude of the contrast control signal output from the microcomputer 10 and applied to the contrast terminal of the video preamplifier 20. And a second transistor Q2 which automatically reduces the contrast of the screen so that the brightness of the screen does not exceed the threshold.

The operation of the automatic brightness control circuit configured as described above is as follows.

First, when a user adjusts the brightness of the screen by operating a key switch, a brightness control signal is output from the microcomputer 10 and applied to the DC bias control unit 22. Accordingly, the DC bias control unit 22 The brightness of the screen is varied by adding a DC bias to the video signals output from the video preamplifier 20 and the video power amplifier 21. That is, when the brightness control signal output from the microcomputer 10 has a large DC value, the DC bias control unit 22 adds a low DC bias control signal to the video signal to increase the brightness of the screen and, conversely, the microcomputer ( If the brightness control signal output from 10) has a small DC value, the DC bias control unit 22 adds a high DC bias control signal to the video signal to lower the brightness of the screen.

In addition, when the user increases the contrast of the screen by adjusting the key switch, a contrast control signal is output from the microcomputer 10 and input to the video preamplifier 20. In this case, the video preamplifier 20 amplifies and outputs an image signal input through a video card according to the magnitude of a contrast control signal input through a contrast terminal. Proportionally amplifies the video signal with a higher gain, and lowering the contrast terminal voltage amplifies the video signal with a lower gain.

If the anode current increases as the contrast increases above the threshold, the ABL voltage output from the ABL terminal of the flyback transformer 30 is lowered to limit the anode current, as shown in FIG. 1. As the ABL current Io flowing into the ABL terminal of the flyback transformer 30 increases, the current I1 input from the 80V power supply also increases. Therefore, since the voltage at the point A shown in FIG. 1 is lower than the emitter voltage of the first transistor Q1, the first transistor Q1 is turned on. When the first transistor Q1 is turned on, the collector voltage at point B is increased. The second transistor Q2 connected to the contrast control signal line of the microcomputer 10 is turned on. As such, when the second transistor Q2 is turned on, the current value of the contrast control signal of the microcomputer 10 at the point C decreases, and accordingly the contrast terminal voltage of the video preamplifier 20 is also lowered. The current is reduced to within the threshold and the contrast of the screen is automatically reduced.

On the other hand, when the anode current is within the threshold, both the first transistor Q1 and the second transistor Q2 are turned off, and the ABL current Io flowing into the ABL terminal of the flyback transformer 30 is a current input from the 80V power supply. Since the value I1 is the same, the current value of the contrast control signal of the microcomputer 10 does not change and the brightness of the screen changes as the user adjusts the keyswitch.

However, since the brightness automatic adjustment circuit as described above can adjust only the contrast of the screen automatically, when the contrast of the screen is automatically reduced while the brightness of the screen is fixed to a constant value, the anode current is limited and the high voltage generation circuit It is possible to prevent the parts from being destroyed, but there is a disadvantage that the sharpness of the screen is reduced. That is, although the brightness of the screen is automatically reduced, the brightness of the screen is fixed, which causes a problem in that characters appearing on the screen appear blurred.

In order to solve the above problems, the present invention automatically changes the contrast of the screen as the ABL voltage output from the ABL terminal of the flyback transformer changes, and simultaneously changes the brightness of the screen. Its purpose is to provide an automatic brightness control circuit for monitors that automatically adjusts brightness as well as brightness.

The present invention devised to achieve the above object, the DC bias control unit outputs a DC bias control signal in accordance with the brightness control signal output from the microcomputer and the DC bias to the video signal output from the video preamplifier and the video power amplifier The brightness of the screen is varied by adding a, the contrast of the video signal input from the video card by the video preamplifier in accordance with the contrast control signal output from the microcomputer, and the contrast according to the ABL voltage output from the flyback transformer. A brightness automatic adjustment circuit of a monitor configured to automatically vary the contrast control signal input to a video preamplifier, wherein the Zener die is turned on when the ABL voltage output from the flyback transformer is greater than the breakdown voltage. Anod and; And a brightness controller including a transistor configured to reduce the voltage of the brightness control signal which is turned on when the zener diode is turned on and is output from the microcomputer and input to the DC bias controller.

According to the circuit of the present invention configured as described above, when the user adjusts the contrast of the screen, the anode current is greater than or equal to the threshold value, and thus, when the ABL voltage output from the flyback transformer decreases, the zener diode and the transistor of the brightness control unit Do not vary the brightness control signal output from the microcomputer and input to the DC bias control unit, and if the ABL voltage output from the flyback transformer increases as the anode current is within a threshold value, the brightness control unit Zener diodes and transistors are turned on to reduce the magnitude of the brightness control signal output from the microcomputer and input to the DC bias control unit, thereby changing the brightness of the screen to reduce the brightness and clarity of the screen. It is to be adjusted.

1 is a diagram illustrating an automatic brightness control circuit ABL of a monitor;

2 is a view showing the automatic brightness adjustment circuit of the monitor according to the present invention.

Explanation of symbols on the main parts of the drawings

10: micom 20: video preamp

21: Video power amplifier 22: DC bias control unit

30: flyback transformer 40: contrast control unit

R1 to R10: resistance ZD1: zener diode

Q1, Q11, Q2: transistor

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a view showing the automatic brightness adjustment circuit of the monitor according to the present invention.

As shown in FIG. 2, according to the embodiment of the present invention, the DC bias control unit 22 outputs a DC bias control signal according to the brightness control signal output from the microcomputer 10 so that the video preamplifier 20 and the video are output. The brightness of the screen is varied by adding a DC bias to the video signal output from the power amplifier 21, and the video preamplifier 20 is input from the video card according to the contrast control signal output from the microcomputer 10. The contrast of the video signal is varied, the monitor for adjusting the contrast control signal input to the video preamplifier 20 by the contrast control unit 40 in accordance with the ABL voltage output from the flyback transformer 30 In the automatic brightness control circuit of the ABL voltage output from the flyback transformer 30 is the breakdown voltage A zener diode (ZD1) and which is larger conduction; Brightness control unit 23 made of a transistor Q3 which is turned on when the zener diode ZD1 is turned on to reduce the voltage of the brightness control signal output from the microcomputer 10 and input to the DC bias control unit 22. It is configured to include).

Referring to the operation of the embodiment according to the present invention configured as described above are as follows.

If the anode current increases as the contrast increases above the threshold, the ABL voltage output from the ABL terminal of the flyback transformer 30 is lowered to limit the anode current, as shown in FIG. 2. As the ABL current Io flowing into the ABL terminal of the flyback transformer 30 increases, the current I1 input from the 80V power supply also increases. Therefore, since the voltage at the point A shown in FIG. 2 is lower than the emitter voltage of the first transistor Q1, the first transistor Q1 is turned on. When the first transistor Q1 is turned on, the collector voltage at point B is increased. The second transistor Q2 connected to the contrast control signal line of the microcomputer 10 is turned on. As such, when the second transistor Q2 is turned on, the current value of the contrast control signal of the microcomputer 10 at the point C decreases, and accordingly the contrast terminal voltage of the video preamplifier 20 is also lowered. The current is reduced to within the threshold and the contrast of the screen is automatically reduced.

In this case, as shown in FIG. 2, since the ABL voltage appearing at the point A becomes lower than the voltage at the point D of the brightness control unit 23, the zener diode ZD1 of the brightness control unit 23 is turned on. At the same time, when the transistor Q3 is turned on, the magnitude of the brightness control signal output from the microcomputer 10 and input to the DC bias control unit 22 is reduced by the resistors R9 and R10 connected to the point E of FIG. 2. Therefore, the DC bias control unit 22 reduces the brightness of the screen by increasing the DC bias control signal added to the video signal.

In other words, when the anode current increases above the threshold, the contrast and brightness of the screen decrease simultaneously, thereby increasing the sharpness of the screen.

On the other hand, when the anode current is within the threshold, both the first transistor Q1 and the second transistor Q2 are turned off, and the ABL current Io flowing into the ABL terminal of the flyback transformer 30 is a current input from the 80V power supply. Since the value of I1 is the same, the current value of the contrast control signal of the microcomputer 10 does not change, and the brightness of the screen changes as the user adjusts the keyswitch. In this case, as shown in FIG. Since the ABL voltage is higher than the voltage at the point D of the brightness control unit 23, both the Zener diode ZD1 and the transistor Q3 of the brightness control unit 23 are turned off. Accordingly, the magnitude of the brightness control signal output from the microcomputer 10 and input to the DC bias control unit 22 does not change, and the DC bias control unit 22 also varies the DC bias control signal added to the video signal. Don't let that happen. In other words, when the anode current is within the threshold, the contrast and brightness of the screen change as the user adjusts the keyswitch.

As described above, according to the present invention, as the ABL voltage output from the ABL terminal of the flyback transformer is changed, the contrast of the screen is automatically changed, and the brightness of the screen is also changed by changing the brightness of the screen. Of course, if the sharpness is automatically adjusted, it provides convenience to the user and stabilizes the performance of the monitor.

Claims (1)

The DC bias control unit 22 outputs the DC bias control signal according to the brightness control signal output from the microcomputer 10 to add a DC bias to the video signals output from the video preamplifier 20 and the video power amplifier 21. Therefore, the brightness of the screen is varied, the video preamplifier 20 varies the contrast of the video signal input from the video card according to the contrast control signal output from the microcomputer 10, and from the flyback transformer 30. In the brightness automatic adjustment circuit of the monitor, the contrast control unit 40 automatically varies the contrast control signal input to the video preamplifier 20 according to the output ABL voltage, A zener diode ZD1 conducting when the ABL voltage output from the flyback transformer 30 becomes greater than the breakdown voltage; Brightness control unit 23 made of a transistor Q3 which is turned on when the zener diode ZD1 is turned on and is output from the microcomputer 10 to reduce the voltage of the brightness control signal input to the DC bias control unit 220. Automatic brightness adjustment circuit of the monitor, characterized in that configured to include.