KR19990002378U - Auto Brightness Limit Circuit of Monitor - Google Patents

Abstract

The present invention relates to an automatic luminance limiting circuit of a monitor capable of displaying screen brightness in various stages.

In the circuit of the present invention, the automatic luminance limiting circuit (ABL) 120 monitors the secondary voltage of the FBT 100 and transmits it to the contrast gain control unit 130 in order to control the screen brightness. In the monitor for adjusting the control voltage, the automatic luminance limiting circuit 120 is turned off when the base end is connected to the microcomputer 110 and the microcomputer 110 outputs the first brightness mode signal H1. The transistor Q3 and the base terminal are connected to the microcomputer 110 so that when the microcomputer 110 outputs the second brightness mode signal H2, the second transistor Q4 is turned off and the base terminal of the first transistor ( The third transistor Q5 connected to the collector terminal of Q3) and the collector terminal of the second transistor Q4, and the base terminal are connected to the emitter terminal of the third transistor Q5, and the collector terminal is connected to the third transistor Q5. Connected to the collector stage of the emitter And a fourth transistor Q6 connected to the ABL terminal and turned on when the third transistor Q5 is turned on, and adjusts the contrast control voltage of the video amplifier according to the brightness mode signal output from the microcomputer. You can adjust the brightness in several steps.

Description

Monitor's automatic luminance limit circuit.

The present invention relates to a screen brightness control technology of the monitor, and more particularly to an automatic brightness limit circuit of the monitor that can be adjusted to the screen brightness in several steps using the ABL.

In general, CRT beam current (i.e. anode current) varies depending on the brightness of the screen. This is a load change from the point of view of the FBT, and the high voltage of the FBT changes with the change of the beam current. In general, when the screen is dark and the beam current is small, the high voltage is high. On the contrary, when the screen is bright, the beam current is increased and the high voltage is low.

First, the operation of the FBT will be briefly described with reference to FIG. 1.

The B + voltage provided by the DC-DC converter 10 is applied to one end of the primary winding of the FBT 30, and the horizontal output unit 20 is connected to the other end thereof. In addition, there are usually a plurality of secondary windings of the FBT, including secondary windings for generating a high voltage, and tertiary windings for monitoring a high voltage induced to the secondary side.

The horizontal output transistor of the horizontal output unit 20 is turned on or off by a horizontal drive signal (H.drive) according to the horizontal synchronous signal. When the horizontal output transistor is turned off, a high voltage is generated in the primary winding. The secondary windings induce the voltage according to the winding ratio, so that the desired voltage can be obtained on the secondary side.

Therefore, the high voltage (HV) applied to the anode of the CRT is used to rectify the voltage induced in the secondary winding of the FBT, and the high voltages (FOCUS, SCREEN) applied to the focus and screen grid of the CRT are also provided at the secondary winding of the FBT. do.

In addition, since the anode voltage of the CRT is a voltage induced in the secondary winding of the FBT, the variation of the anode voltage can be detected by monitoring the secondary voltage of the FBT using another auxiliary winding (third winding).

On the other hand, the FBT has an automatic brightness limit (ABL) circuit for controlling the brightness of the screen by monitoring the anode current.

Referring to FIG. 1, when the luminance is abnormally high, the ABL circuit 40 is a circuit for preventing a large anode current from flowing and overloading the high voltage generating circuit to destroy components. To this end, a change in the anode current is detected and fed back to the brightness control voltage or contrast control voltage to apply the ABL. That is, when the brightness increases and the anode current exceeds the threshold, the anode current is limited by lowering the contrast control voltage of the video amplifier 60.

At this time, since the 80V power is normally applied through the resistor R1, when the brightness of the screen is normal, a voltage of about 12V to 15V is applied to the point A. When the brightness of the screen becomes bright, a voltage of 12V or less is applied to the point A. Accordingly, the PNP transistor Q1 is turned on and a low voltage is applied to the base terminal of the NPN transistor Q2. Therefore, the emitter voltage of the NPN transistor Q2 is lowered and transmitted to the contrast gain control unit 50. Accordingly, since the contrast control voltage of the video amplifier 60 is lowered, the video amplifier 60 lowers the brightness of the screen.

As such, conventionally, by lowering the screen brightness using ABL when the screen is bright and increasing the screen brightness when the screen is dark, it is not supported to change the brightness to another mode because the brightness of the screen is adjusted to only one state.

Accordingly, an object of the present invention is to provide an automatic luminance limiting circuit of a monitor for displaying the screen brightness of the monitor in various stages.

The circuit of the present invention for achieving the above object, the automatic luminance limiting circuit monitors the secondary voltage of the FBT in order to control the screen brightness and transmits it to the contrast gain control unit to monitor the contrast control voltage of the video amplifier The automatic luminance limiting circuit may include a first transistor which is turned off when a base terminal is connected to a microcomputer and the microcomputer outputs a first brightness mode signal, and a base terminal is connected to a microcomputer and the microcomputer outputs a second brightness mode signal. A second transistor that is turned off, a third transistor having a base end coupled to a collector end of the first transistor and a collector end of a second transistor, and a base end connected to an emitter end of the third transistor, and a collector end being connected to the third transistor. The third transistor is connected to the collector terminal of the transistor and the emitter terminal is connected to the ABL terminal. The fourth transistor is turned on when the jitter is turned on.

1 is a circuit diagram showing a general automatic luminance limiting circuit in a monitor;

2 is a circuit diagram showing a brightness mode adjusting apparatus of the monitor according to the present invention.

＊ Explanation of symbols for main parts of drawing

100: flyback transformer (FBT) 110: micom

120: automatic luminance limiting circuit (ABL) 130: contrast gain control unit

140: video amplifier Q1, Q2, Q3, Q4, Q5, Q6: transistor

R1, R2, R3, R4, R5: Resistance

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a circuit diagram illustrating an automatic luminance limiting circuit of the monitor according to the present invention.

As shown in FIG. 2, the circuit of the present invention includes an FBT 100, a microcomputer 110, an automatic luminance limiting circuit (ABL) 120, a contrast gain control unit 130, and a video amplifier 140. .

The ABL 120 according to the present invention has a base transistor having a first transistor Q3 connected with a first brightness mode signal H1, a base transistor having a second transistor Q4 connected with a second brightness mode signal H2, and a base. A third terminal Q5 connected to a collector terminal of the first transistor Q3 and a collector terminal of the second transistor Q4, and a base terminal are connected to an emitter terminal of the third transistor Q5, and the collector terminal is connected. A predetermined power is applied to the collector terminal by being connected to the collector terminal of the third transistor Q5 and the emitter terminal includes a fourth transistor Q6 connected to the ABL terminal.

The operation of the present invention configured as described above will be described according to the brightness mode.

First, in the normal brightness mode, since the voltage of the node A 'is about 12V to 15V, the PNP transistor Q1 is turned off. Accordingly, a high voltage is applied to the base of the NPN transistor Q2 and turned on, and the emitter voltage of the NPN transistor Q2 is increased to be transmitted to the contrast gain control unit 130.

In the case of the first brightness mode, the microcomputer 110 outputs a first brightness mode signal H1 having a 'low' level. Accordingly, the first transistor Q3 is turned off and the 80 V power is turned off through the first transistor Q3 which is turned off, and the voltage rising up by the resistor R4 is applied to the base terminal of the third transistor Q5. Is approved. Therefore, as the third transistor Q5 is turned on to amplify the voltage and the fourth transistor Q6 is turned on, the voltage at the point A ′ increases.

When the reverse current flows to the collector terminal of the PNP transistor Q1 due to the reverse bias, a 12V power supply is applied to the base terminal of the NPN transistor Q2 through the parallel resistors R2 and R3, thereby providing the NPN transistor Q2. Is turned on. Accordingly, since the emitter voltage of the NPN transistor Q2 is increased to be transmitted to the contrast gain control unit 130, the contrast control voltage of the video amplifier 140 is increased to brighten the screen.

In the second brightness mode, which is one step brighter than the first brightness mode, the microcomputer 110 outputs the second brightness mode signal H2 having a 'low' level, so that the second transistor Q4 is turned off. As a result, a voltage of 80 V is turned on through the turned-off second transistor Q4 and the voltage increased by the resistor R5 is applied to the base terminal of the third transistor Q5. Therefore, as the third transistor Q5 is turned on to amplify the voltage and the fourth transistor Q6 is turned on, the voltage at the A 'point becomes higher.

As a result, a larger reverse current flows to the collector terminal of the PNP transistor Q1 due to a reverse bias, and a higher voltage is applied to the base of the NPN transistor Q2, thereby turning on the NPN transistor Q2. Thus, the emitter voltage of the NPN transistor Q2 is increased and the contrast control voltage of the video amplifier 140 is increased by the contrast gain control unit 130 so that the video amplifier 140 makes the screen brighter.

As described above, the circuit of the present invention has the effect of adjusting the brightness of the screen in several stages by adjusting the contrast control voltage of the video amplifier according to the brightness mode signal output from the microcomputer.

Claims (1)

The automatic luminance limiting circuit (ABL) 120 monitors the secondary voltage of the FBT 100 and transmits it to the contrast gain control unit 130 in order to control the screen brightness, thereby controlling the contrast control voltage of the video amplifier 140. In The automatic luminance limiting circuit 120 is A first transistor Q3 which is turned off when the base terminal is connected to the microcomputer 110 and the microcomputer 110 outputs the first brightness mode signal H1; A second transistor Q4 that is turned off when the base terminal is connected to the microcomputer 110 and the microcomputer 110 outputs the second brightness mode signal H2; A third transistor Q5 having a base terminal connected to the collector terminal of the first transistor Q3 and the collector terminal of the second transistor Q4; And The base terminal is connected to the emitter terminal of the third transistor Q5, the collector terminal is connected to the collector terminal of the third transistor Q5, and the emitter terminal is connected to the ABL terminal so that the third transistor Q5 is turned on. An automatic luminance limiting circuit of a monitor comprising a fourth transistor (Q6).