KR19990028797U - CRT protection device of the monitor - Google Patents

Abstract

The present invention relates to a CRT protection device that suppresses electrons emitted from the cathode to the fluorescent film when the mute function is required when the power is turned off or the mode is switched. An electrolytic capacitor that charges the power voltage applied from the power generator and generates counter electromotive force when the power of the monitor is turned off; A transistor that is turned on when the power of the monitor is turned off so that the counter electromotive force of the electrolytic capacitor is applied to the control grid of the CRT to boost the negative voltage of the control grid; A plurality of resistors for turning on the transistor when the counter electromotive force of the electrolytic capacitor is greater than the negative voltage output from the high voltage generator; And a diode that provides a flow path when the transistor is turned on so that the counter electromotive force of the electrolytic capacitor is applied to the control grid.

Therefore, the present invention protects the CRT from the spot by weakening the spot by increasing the negative voltage applied to the control grid more quickly when the monitor is turned off, thereby preventing the life of the CRT from being shortened. It has an effect.

Description

An apparatus for protecting a CRT in a monitor

The present invention relates to a protection device for a CRT of a monitor, and more particularly, to a CRT protection device that suppresses electrons emitted from a cathode to a fluorescent film when a mute function is required during power off or mode conversion.

In general, a monitor is a device that receives information from a computer video card and a synchronization signal and displays information on a CRT screen. The monitor includes a video system for processing a video signal, a deflection system for vertical and horizontal deflection, and a power supply. It consists of a system.

In this case, the video card outputs various horizontal and vertical frequencies according to modes, and a monitor compatible with at least two video modes is called a multi-mode monitor.

In the above-described multi-mode monitor, supplying a voltage (rated voltage) necessary for each monitor circuit at the time of power on / off or mode switching of the monitor may cause an abnormality in each monitor circuit. At the beginning of the mode conversion, it is necessary to supply a ready voltage lower than the rated voltage and then supply the rated voltage so that each monitor circuit can warm up and perform normal operation. This is called a mute function, and a mute signal for performing the mute function is output from the microcomputer.

The mute signal maintains a low level during normal operation and then transitions to a high level during power on / off or mode switching. At this moment, the amount of electrons emitted from the cathode to the fluorescent film is boosted by boosting the control grid signal supplied to the CRT. Suppresses the occurrence of spots.

The spot is a small light point generated by an electron beam colliding with a fluorescent film of a CRT. When the monitor is turned on, the cathode (cathode) of the electron gun is sufficiently heated to emit electrons. The electrons collide with the fluorescent film to generate spots.

The spot is used to display an image on a CRT screen. When the spot on the fluorescent film is deflected from side to side, the raster is made, and the brightness of the spot is changed by an image signal during the process of making the raster. The desired image is displayed on the CRT screen.

At this time, the spot can be adjusted by the control grid (G1) current supplied to the CRT (120) from the FBT (Flay-Back Transformer), the control grid (G1) current is emitted from the cathode of the CRT (120) Controlling the amount of electrons controls brightness modulation (brightness modulation).

That is, the larger the negative voltage is supplied to the control grid G1, the greater the power for suppressing the electron emission of the cathode, so that the amount of electrons colliding with the fluorescent film is reduced and the screen is darkened by weakening the spot.

FIG. 1 is a block diagram of a general CRT protection device. Referring to FIG. 1, when a mute function of a general CRT protection device is performed, an AC voltage is output from a FBT and negatively rectified when power is supplied to a monitor. (Normally -80V) is then supplied to the control grid G1 of the CRT 120.

In addition, the mute signal processor 140 drops the DC voltage of -80V supplied from the high voltage generator 110 at about -60V during normal operation, that is, when the mute signal is at a low level, thereby controlling the control grid of the CRT 120. G1) and when the mute signal becomes high during mode conversion, the DC voltage of -80V supplied from the high voltage generator 110 is supplied to the control grid G1 of the CRT 120 as it is.

Accordingly, since the control grid G1 voltage input to the CRT 120 increases from -60V to -80V when the mute function is performed, the screen is darkened by suppressing electron emission by that much.

The spot can be sufficiently suppressed in the same manner as described above because the deflection circuit is driven during the mode switching of the monitor. However, when the monitor is powered off, the electrons outputted by the heated cathode while the deflection circuit is stopped are driven. Since the spot is generated by hitting the center of the screen, the damage of the CRT screen due to the spot cannot be prevented.

In other words, when the power is turned off, only by adjusting the negative voltage of the control grid G1 using the mute function, the effect cannot be greatly seen. Therefore, the monitor generally uses an additional spot killer circuit 160. To weaken the spot by making the negative voltage supplied to the control grid G1 even larger.

The conventional spot killer circuit is shown in FIG. 2. When the monitor operates normally, since the high level signal is output from the power generator 150, the first transistor Q1 is turned on and the second transistor Q2 is turned on. ) Is turned off and the third transistor Q3 is turned on so that the driving power source Vcc2 is charged to the capacitor C1 through the third transistor Q3.

In this state, when the monitor is powered off and the operation of the power generator 150 is stopped, a low level signal is output from the power generator 150. As a result, the first transistor Q1 is turned off, and The second transistor Q2 is turned on and the third transistor Q3 is turned off. At this time, when the third transistor Q3 is turned off, the energy between both ends of the capacitor C1 is converted into a reverse potential by the principle of energy conservation, so that the negative potential portion of the capacitor C1 is changed to a lower negative potential. The negative voltage of the control grid G1 increases to weaken the spot.

That is, when the monitor is powered off, the mute signal processing unit 140 and the spot killer circuit 160 simultaneously operate to boost the negative voltage applied to the control grid G1 to greatly increase the amount of electrons that strike the fluorescent film. Significantly reduced.

However, the spot killer circuit needs to quickly boost the negative voltage applied to the control grid to remove the CRT electron beam before the electron beam collects at the center of the CRT when the monitor is powered off. Since the negative voltage is supplied to the control grid through several switching operations when the power is turned off, it takes a long time to remove the spot and thus does not perform a perfect spot killer function.

Accordingly, the present invention has been made to solve the problems of the prior art as described above, and the object of the present invention is to provide a CRT protection device for a monitor to which a spot killer circuit can be effectively weakened in a short time when the monitor is turned off. have.

The CRT protection device of the present invention for achieving the above object is a CRT protection device having a spot killer circuit for increasing the negative voltage applied to the control grid when the power of the monitor is turned off, the spot The killer circuit may include an electrolytic capacitor that charges a power voltage applied from a power generator when the monitor is turned on and generates counter electromotive force when the monitor is turned off; A transistor that is turned on when the power of the monitor is turned off so that the counter electromotive force of the electrolytic capacitor is applied to the control grid of the CRT to boost the negative voltage of the control grid; A plurality of resistors for turning on the transistor when the counter electromotive force of the electrolytic capacitor is greater than the negative voltage output from the high voltage generator; And a diode providing a flow path so that when the transistor is turned on, the counter electromotive force of the electrolytic capacitor is applied to the control grid.

1 is a block diagram showing a general CRT protection device,

2 is a circuit diagram showing a conventional spot killer circuit;

3 is a circuit diagram illustrating a CRT protection device of a monitor to which a spot killer circuit according to the present invention is applied.

* Names of symbols for main parts of the drawings

110: high pressure generating unit 120: CRT

130: micom 140: mute signal processing unit

150: power generation unit 160,200: spot killer circuit

G1: control grid

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

3 shows a spot killer circuit according to the present invention, which charges a power voltage applied from the power generator 150 when the monitor is turned on and generates electromotive force when the monitor is turned off. When the power of the capacitor C21 and the monitor is turned off, the electromotive capacitor C21 is turned on so that the counter electromotive force is applied to the control grid G1 of the CRT so that the negative voltage of the control grid G1 is boosted. It consists of transistor Q21.

In more detail, one end of the power generation unit 150 and the electrolytic capacitor C21 is connected, and the other end of the electrolytic capacitor C21 is connected to the output terminal of the high voltage generator 110 through the diode D22. At the same time, it is connected to the emitter terminal of transistor Q21. The cathode end of the diode D22 is connected to the base end of the transistor Q21 via a resistor R21, and the anode end of the diode D22 is connected to the emitter end of the transistor Q21. In addition, a resistor R22 and a resistor R23 are connected in series between the base terminal and the ground terminal of the transistor Q21, and the common contact of these resistors is connected to the emitter terminal of the transistor Q21. The collector end of transistor Q21 is connected to control grid G1 of the CRT via diode D21.

Looking at the operation of the present invention configured as described above are as follows.

When the monitor operates in a normal state, the power generator 150 normally drives and outputs a power voltage, which is charged by the electrolytic capacitor C21. At this time, a negative voltage of about −80 V is output from the high voltage driver 110, and the negative voltage is applied to the control grid G1 of the CRT. Of course, when an inactive mute control signal is output from the microcomputer, a negative voltage of -80V is stepped down to -60V through a mute signal processor and then applied to the control grid, and when an active mute control signal is output from the microcomputer- A negative voltage of 80V is applied directly to the control grid to boost the negative voltage, which weakens the spot when the mute function is performed.

As described above, when the monitor is normally driven, since the base terminal voltage of the transistor Q21 is lower than the emitter terminal voltage, the transistor Q21 remains turned off, and a negative voltage of -80 V to -60 V is controlled. Applied to (G1).

On the other hand, when the power of the monitor is turned off, the power supply voltage applied from the power generation unit 150 to the electrolytic capacitor C21 is lowered to a low level. Is generated. That is, the negative potential voltage of the electrolytic capacitor C21 is output as a lower negative voltage, and at this time, the transistor Q21 is increased because the base terminal voltage of the transistor Q21 becomes higher than the conduction voltage than the emitter terminal voltage. Turn on.

As described above, when the transistor Q21 is turned on, the counter electromotive force of the electrolytic capacitor C21 is applied to the control grid G1 of the CRT through the diode D21, and the negative voltage applied to the control grid is greatly boosted to further spot the spot. More weakened.

As described above, the present invention protects the CRT from the spot by weakening the spot by allowing the negative voltage applied to the control grid to be boosted more quickly when the monitor is turned off, thereby protecting the CRT from the spot. It is effective to prevent shortening.

Claims (1)

In the CRT protection device provided with a spot killer circuit to increase the negative voltage applied to the control grid when the monitor is powered off, The spot killer circuit may include an electrolytic capacitor that charges a power voltage applied from a power generator when the monitor is turned on and generates counter electromotive force when the monitor is turned off; A transistor that is turned on when the power of the monitor is turned off so that the counter electromotive force of the electrolytic capacitor is applied to the control grid of the CRT to boost the negative voltage of the control grid; A plurality of resistors for turning on the transistor when the counter electromotive force of the electrolytic capacitor is greater than the negative voltage output from the high voltage generator; And And a diode for providing a flow path so that the counter electromotive force of the electrolytic capacitor is applied to the control grid when the transistor is turned on.