KR20000028431A - Circuit for adjusting brightness in shifting mode of monitor - Google Patents

Abstract

PURPOSE: A circuit adjusting brightness, in a shifting mode of a monitor is provided to give a mode signal by inputting a horizontal/vertical synchronization signal to a micom, and by automatically deciding a text mode or a graphic mode to turn on/off a transistor according to the mode signal, to highly/lowery adjust a contrast signal, and to adjust brightness of the screen when shifting the mode. CONSTITUTION: A circuit for adjusting brightness of a screen in a shifting mode of a monitor comprises a video free amplifier(210), a video power amplifier(220), a micom(230), key inputter(240), a contrast adjusting circuit, a contrast adjusting device, a first transistor(Q11), and a second transistor(Q12). The video free amplifier amplifies an R.G.B(Red-Green-Blue) signal inputted through a video card of a computer, and adjusts brightness in reference to a contrast signal. The video power amplifier drives a cathode of a CRT(Cathode Ray Tube) by amplifying output of the video free amplifier. The contrast adjusting device induces the contrast signal adjusted through predetermined first/second split resistance(R11, R12) and variable resistance(VR1). The micom is received a horizontal/vertical synchronization signal, and outputs a mode signal by deciding a graphic mode or a text mode. The first transistor is turned on in the text mode, and turned off in the graphic mode, in reference to the mode signal of the micom. The second transistor adjusts the contrast signal lower by flowing current through the first/second split resistance in the text mode, by being reversely operated with the first transistor, and highly adjusts the contrast signal by flowing the only first split resistance, through bypassing the second split resistance in the graphic mode.

Description

Circuit for changing brightness according to modes in a monitor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for adjusting the contrast & brightness of a screen in a monitor used as a display device of a computer. More particularly, the present invention relates to a screen brightness control circuit for changing a mode for adjusting the brightness of a screen according to a mode.

In general, the brightness of the screen displayed on the monitor can be arbitrarily set by the user by adjusting the contrast and BRIGHTNESS knobs.

Still screens displayed on monitors were generally as still images as in word processing applications. However, with the development of video encoding technology, MPEG boards have been developed to display moving images on monitors. As a result, the normal brightness level when displayed mainly on a still image (called 'text mode') and the high contarst level when displayed mainly on a moving image (called 'graphic mode') It was necessary to adjust the brightness according to the mode.

However, since the optimal screen brightness for displaying still images and the optimal screen brightness for displaying moving images are different from each other, conventionally, when executing an application program that focuses on still images and then runs an application program that focuses on moving images It was very inconvenient because I had to readjust the brightness of the screen.

If this is explained in more detail as follows.

Figure 1 is a schematic diagram showing the part related to the brightness of the screen in a typical monitor, R, G, B video signal input from the computer through a 15-pin D-sub connector (not shown) is a video pre-amplifier (video pre- Amplified first at AMP: 110 and then amplified again at video output amplifier 120 to drive each of the cathodes K1, K2, K3 of CRT 130.

That is, since the video signal input through the D-sub connector is a low signal of about 1V or less, the video preamplifier 110 is amplified with an AC gain of about 4 to 10 and then the cathode of the CRT is output from the video output amplifier 120. Amplify the signal from approximately 30V to 50V to drive. Since the video output amplifier CRT driver 120 is a fixed gain amplifier, the video preamplifier 110 can adjust the level of the video signal. Examples include LM1203, LM1203A, LM1204, LM1207, and LM1208 of NS Corporation.

The level of the video signal of the video preamplifier 110 may be analogically adjusted by a resistance value of the variable resistor VR1 connected to a contrast adjusting knob which may be variable by a user, as shown in FIG. 1. Can be. That is, when the user adjusts the variable resistor VR1, the base voltages of the transistors Q1, Q2, and Q3 are changed accordingly, and R, G, and B connected through a resistor to the collector side of each transistor Q1, Q2, and Q3. The signal input to the contrast adjustment terminal is varied so that the video preamplifier 110 adjusts the amplification degree of the R, G, and B video signals.

On the other hand, the brightness of the screen displayed on the CRT is also possible by adjusting the voltage applied to the first grid (G1) of the CRT, as shown in Figure 1-the voltage rectified on the secondary side of the FBT 140 is brightness The brightness of the screen can be adjusted by being applied to the first grid G1 after being changed by the variable resistor VR2 connected to the adjustment knob. That is, the R, G, and B image signals drive the cathodes K1, K2, and K3 of the CRT, respectively, wherein the amount of hot electrons emitted and reaching the fluorescent film is applied to the first grid G1. ) Varies according to the magnitude of the voltage. For example, as the negative voltage applied to the first grid G1 approaches zero, the amount of hot electrons passing through increases to brighten the screen, and when the absolute value increases to the negative side, the amount of hot electrons decreases to darken the screen.

As such, the method of controlling the brightness of the screen varies the amplification degree of the video preamplifier to directly adjust the size of the video signal, and the thermoelectrics that reach the fluorescent film by varying the voltage applied to the first grid G1 of the CRT. There is a method of controlling the amount of this, by dividing it is usually called the contrast (contrast) control and the latter is called the brightness control (BRIGHTNESS).

However, in the conventional method of adjusting the brightness of the screen as described above, it is very inconvenient because the user adjusts the brightness level according to the mode by adjusting the contrast adjusting knob (or the brightness adjusting knob).

Accordingly, an object of the present invention is to provide a screen brightness control circuit when a mode is changed in a monitor that recognizes a mode and automatically adjusts a brightness level when a mode is changed.

In order to achieve the above object, the present invention, a contrast control means for generating a contrast signal, which is controlled through the predetermined first and second split resistors and the variable resistor to provide to the video preamplifier; A microcomputer that receives a horizontal synchronous signal and a vertical synchronous signal to discriminate the graphic mode and the text mode and output a mode signal; A first transistor turned on in a text mode according to the mode signal of the microcomputer and turned off in a graphic mode; In contrast to the first transistor, the current flows through the first and second split resistors in the text mode to lower the contrast signal. In the graphic mode, the second split resistor is bypassed and the current flows through only the first split resistors. And a second transistor for adjusting the contrast signal to a high level.

1 shows a video system in a monitor;

2 is a circuit diagram illustrating a screen brightness control circuit when a mode is changed in a monitor according to the present invention.

* Explanation of symbols for main parts of the drawings

210: video preamplifier 220: video power amplifier

230: micom 240: key input unit

Q11: first transistor Q12: second transistor

Q13: third transistors R11 to R14: split resistance

VR1: Variable resistor

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

2 is a diagram showing a circuit for automatically changing the brightness of the screen when the mode change in accordance with the present invention. Referring to FIG. 2, the circuit of the present invention includes a video preamplifier 210 for amplifying R, G and B signals input through a video card of a computer and adjusting brightness according to contrast signals, and a video preamplifier 210. It consists of a video power amplifier 220, a microcomputer 230, a key input unit 240, a contrast control circuit for driving the cathode of the CRT by amplifying the output.

The contrast control circuit divides the 100V voltage through the first to fourth split resistors R11 to R14 to apply the voltage to the base of the third transistor Q13, and the emitter of the third transistor Q13 is connected to the 12V voltage. Contrast adjusting means adapted to adjust a contrast signal of the video preamplifier 210 through a variable resistor VR1 connected to the collector of the third transistor Q13; The first and second transistors Q11 and Q12 adjust brightness in the text mode and the graphic mode according to the mode signal of the microcomputer 230.

The microcomputer 230 receives horizontal and vertical synchronization signals H.sync and Vsync to determine the text mode and the graphics mode, and outputs a high in the text mode and a low in the graphics mode. Therefore, the mode signal is changed from high to low when changing from text mode to graphics mode, and the mode signal is changed from low to high when changing from graphics mode to text mode.

The first transistor Q11 is turned on by the high signal of the text mode, and thus the base terminal of the second transistor Q12 is turned low, and the second transistor Q12 is turned off. Accordingly, in the contrast signal, the 100V voltage is divided by the first to fourth split resistors R11 to R14, and the current i5 flows through the first split resistor R11 and the second split resistor R12. The current i3 flowing through the resistor R13 is the sum of the current i1 flowing through the FBT and the current i2 flowing through the resistor R14, and the current i5 is the current i4 flowing from the resistor R13 and the current i4 flowing from the base side of the third transistor Q13. Sum of

When the microcomputer 230 detects the change to the graphics mode and changes the mode signal from high to low, the first transistor Q11 is turned off. When the first transistor Q11 is turned off, high is applied to the base of the second transistor Q12 so that the second transistor Q12 is turned on. When the second transistor Q12 is turned on, most of the current flows through the second transistor Q12 connected in parallel to the second split resistor R12, and the second split resistor R12 is bypassed. Therefore, the 100V voltage is divided by the first, third, and fourth split resistors R11, R13, and R14, and the current i5 becomes large. When the current i5 becomes large, the current i3 is almost constant, so that the current i4 decreases, thereby increasing the current flowing through the variable resistor VR1, thereby increasing the contrast signal.

As such, in the graphical mode, the contrast signal is increased according to the mode signal of the microcomputer 230, and the screen becomes brighter.

As described above, according to the present invention, the microcomputer receives the horizontal and vertical synchronous signals and determines whether the text mode is the text mode or the graphics mode, and provides a mode signal. The transistor is turned on / turned off according to the mode signal. By adjusting the contrast signal high or low, you can get the picture with the appropriate brightness depending on the mode.

Claims (1)

Contrast adjusting means for generating a contrast signal controlled through predetermined first and second split resistors R11 and R12 and the variable resistor VR1 and providing the contrast signal to the video preamplifier 210; A microcomputer 230 for receiving a horizontal synchronous signal and a vertical synchronous signal to determine a graphic mode and a text mode and output a mode signal; A first transistor Q11 turned on in a text mode according to the mode signal of the microcomputer and turned off in a graphic mode; And In contrast to the first transistor Q11, the current flows through the first and second division resistors R11 and R12 in the text mode to lower the contrast signal, and the second division resistor R12 in the graphic mode. And a second transistor (Q12) for controlling the high contrast signal by allowing current to flow through only the first division resistor (R11) by bypassing the screen brightness adjusting circuit when the mode is changed.