KR100195753B1 - Apparatus for protecting crt - Google Patents

Abstract

The present invention relates to a CRT protection apparatus, and an apparatus of the present invention includes a high voltage generating unit (10) for supplying a negative voltage to a control grid (20) of a CRT; And a microcomputer (30) for outputting a mute signal of a first level during normal operation and a mute signal of a second level during power on / off or mode conversion, When the first level mute signal is input, the negative voltage outputted from the high voltage generating unit 10 is lowered and supplied to the control grid 20. When the mute signal of the second level is inputted, A mute signal processing unit (40) which supplies the control voltage to the control grid (20), further boosts the negative voltage when the power is off, and supplies the voltage to the control grid (20); A luminance signal processor 50 for changing the magnitude of the negative voltage supplied to the control grid 20 by the luminance signal; Off cutout determination unit 60 that cuts off the energy supplied to the control grid 20 from the high voltage generating unit 10, the mute signal processing unit 40 and the luminance signal processing unit 50, So that the CRT is protected by varying the negative voltage supplied to the control grid 20 during the mute operation, the power off, or the luminance signal change.

Description

An apparatus for protecting a CRT (CRT)

[0001] The present invention relates to a CRT protection device, and more particularly, to a CRT protection device adapted to protect a CRT by varying a minus voltage supplied to a control grid of a CRT during a mute operation, a power- .

Generally, if the voltage (rated voltage) necessary for each monitor circuit at the time of power on / off of the monitor or during the mode conversion is supplied at once, it will cause an error in each monitor circuit. Therefore, It is necessary to supply the rated voltage after supplying the ready voltage lower than the rated voltage so that the circuit can perform normal operation after warming up. 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 for a while during power on / off or during mode conversion. At this moment, the control grid signal of -DC voltage supplied to the CRT is stepped up from the cathode to the fluorescent film Thereby suppressing the amount of electrons emitted.

In general, a spot is a small light spot generated when an electron beam collides with a fluorescent film of a CRT. When the monitor is powered on, the cathode (cathode) of the electron gun is sufficiently heated to emit electrons. A spot is generated by being hit against the fluorescent film.

In order to display a picture on the CRT, one of the spots should be displayed on the fluorescent film, and the spot should be deflected horizontally and vertically to make a raster and to change the brightness of the spot as a video signal.

Such a spot can be controlled by a control grid current supplied to the CRT from a flyback transformer (FBT), which controls the amount of electrons emitted from the cathode of the CRT to control the luminance modulation (brightness modulation).

At this time, as the negative voltage is supplied to the control grid 20 largely, the force for suppressing the electron emission of the cathode becomes greater, so that the quantity of electrons colliding with the fluorescent film is reduced and the spot is weakened to darken the screen.

1 is a block diagram of a general CRT protection device. Referring to FIG. 1, when the general CRT protection device performs a mute function, AC voltage is output from a flyback transformer (FBT) (-) rectification (normally -80 V).

The mute signal processing unit 40 generates a DC voltage of -80 V from the high voltage generating unit 10 when the mute signal is at a normal level, And supplies the DC voltage of -80 V supplied from the high voltage generating unit 10 to the control grid 20 of the CRT as it is at the time of mode conversion, that is, when the mute signal becomes high level.

Therefore, when the mute function is performed, the voltage of the control grid 20 input to the CRT is increased from -60V to -80V.

In particular, when the power supply of the monitor is turned off, the charged cathode remains charged for a long time due to the electrostatic capacity applied between the inner conductive film and the outer conductive film, And absorbs a small amount of electrons emitted from the cathode to generate a spot.

However, since the deflection circuit stops operating due to the power-off, the emitted electrons are not deflected and are emitted to the center of the CRT, and hit the fluorescent film, so that the spot is strongly generated.

Therefore, when the power is turned off, the effect of the negative (-) voltage of the control grid 20 is merely adjusted by using only the mute function. Therefore, in general, the spot killer circuit 50 is additionally used, (-) voltage to be supplied to the photodiode 20 is further increased to weaken the spot.

In addition, a luminance signal of a DC voltage whose level is variable is output from the microcomputer 30 according to a user's request, and the luminance (brightness) of the screen can be adjusted by varying the control grid signal. Generally, in the CRT, a luminance signal processing unit 60 is provided.

As described above, the conventional CRT protection device has a complicated circuit structure for changing the control grid voltage at the time of mute operation, power-off, or luminance signal variation, and the circuit operation is also complicated.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a CRT having a simple structure in which a negative voltage to be supplied to a control grid of a CRT is variably changed during a mute operation, The object of the present invention is to provide a CRT protection device adapted to protect a CRT.

According to an aspect of the present invention, there is provided a CRT protecting apparatus comprising: a high voltage generating unit for rectifying an AC voltage generated from a flyback transformer to a DC voltage and supplying the AC voltage to a control grid of a CRT; Outputs a first level mute signal during normal operation and then outputs a second level mute signal at a power on / off state or during a mode transition for a while, the second level being a level opposite to the first level, A negative voltage output from the high voltage generator is supplied to the control grid of the CRT when the mute signal of the first level is received, And supplies the negative voltage to the control grid of the CRT when the second level mute signal is received and supplies the negative voltage to the control grid of the CRT when the power is off, A signal processing unit; A luminance signal processor for changing a magnitude of a negative voltage supplied to the control grid of the CRT by a luminance signal input from the microcomputer; And a cutoff determining unit for cutting off energy supplied to the CRT control grid from the high voltage generating unit, the mute signal processing unit, and the luminance signal processing unit, with a constant brightness as a boundary.

That is, the present invention is adapted to protect the CRT by varying the negative voltage supplied to the control grid of the CRT when the mute operation, the power-off, or the luminance signal is varied.

1 is a block diagram showing a general CRT protecting apparatus,

2 is a circuit diagram showing a CRT protecting apparatus according to the present invention.

* Name of designator for main part of the drawing

10: High-voltage generating unit 20: CRT

30: microcomputer 40: mute signal processing section

50: luminance signal processor 60: cutoff decision unit

D 1,2,3,4: Diode C 1,2,3,4,5: Capacitor

Q 1,2,3,4,5,6: transistors 1,2,3,4,5,6

R 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17: Resistance

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

2 is a circuit diagram showing a CRT protecting apparatus according to the present invention.

2, the CRT protecting apparatus according to the present invention includes a high voltage generating unit 10, a control grid 20 of a CRT, a microcomputer 30, a mute signal processing unit 40, a luminance signal processing unit 50); And a cut-off determining unit 60. FIG.

The mute signal processing unit 40 includes a voltage lower portion 41 for lowering the supplied voltage; A switching driver (42) for receiving the mute signal and outputting a driving signal; (-) voltage is supplied to the control grid as it is, and a negative (-) voltage supplied in the off state is supplied to the CRT through the voltage lower part 41 A switching unit (43) for supplying the control grid (20); And a charging unit 44 that charges a predetermined voltage in normal operation and increases the negative voltage of the control grid 20 by converting energy between the opposite ends when the power is turned off,

The switching driver 42 includes a first transistor Q1 having a base end connected to the mute signal, a collector terminal connected to the power supply voltage Vcc, and an emitter terminal grounded; And a second transistor Q2 whose base end is connected in parallel between the power supply voltage Vcc and the collector terminal of the first transistor Q1 and whose emitter terminal is connected to the power supply voltage Vcc, The switching unit 43 has a base end connected to the collector terminal of the second transistor Q2 and a collector terminal connected to the control grid 20 of the CRT. An emitter terminal of the switching unit 43 is connected to the flyback transformer FBT, And a third transistor Q3 receiving a voltage.

The voltage lower part 41 is connected in parallel to one end of the first resistor R8 between the flyback transformer FBT and the emitter terminal of the third transistor Q3, And the other end of the second resistor R9 is connected in parallel between the collector terminal of the third transistor Q3 and the control grid 20 of the CRT. And the charging unit 44 includes a capacitor C3 connected between a collector terminal and an emitter terminal of the third transistor Q3.

The luminance signal processing unit 50 includes a fifth transistor Q5 having a base terminal receiving a luminance signal from the microcomputer 30 and an emitter terminal connected to the control grid 20 of the CRT; And a collector terminal of the fifth transistor Q5 is connected to the control grid 20 of the CRT and an emitter terminal of the fifth transistor Q5 is connected to the flyback transformer FBT via the resistor R17, And a sixth transistor Q6 connected in parallel between the lower part 41 of the first transistor Q1 and the fifth transistor Q6 connected in parallel between the lower part 41 and the lower part 41. The cutoff determining part 60 has a third resistor R12 and a fourth resistor R13, And a control terminal connected in parallel between the emitter terminal of the fifth transistor Q5 and the control grid 20 of the CRT and having a collector terminal connected to the first resistor R8 and a base terminal connected to the second resistor R9 .

Hereinafter, the operation and effects of the present invention will be described.

Referring to FIG. 2, the operation of the mute signal processing unit 40 according to the present invention will be described. First, when power is supplied to the monitor and an AC voltage is output from the flyback transformer FBT, , And the rectified-DC voltage (typically -80 V) is smoothed through the capacitor C1.

At this time, when the mute signal processing unit 40 receives a mute signal of a first level (for example, a low level in this embodiment) from the microcomputer 30 during normal operation, The power supply voltage Vcc (for example, 120 V) is supplied to the base end of the second transistor Q2 through the resistor R4 as the first transistor Q1 is turned off, The second transistor Q2 is turned off so that a low level signal is applied to the base end of the third transistor Q3 so that the third transistor Q3 is turned off.

The DC voltage of -80 V outputted from the high voltage generating part 10 is lowered to about -60 V through the resistors R8 and R9 to turn on the control grid 20 of the CRT as the third transistor Q3 is turned off, (The fourth transistor Q4 maintains the turn-on state during normal operation).

If the mute signal momentarily transitions to a second level (for example, a high level in this embodiment) which is a level opposite to the first level for a few seconds when the power is turned on / off or during mode conversion, The power source voltage is applied to the emitter terminal of the first transistor Q1 through the resistors R3 and R2 as the first transistor Q1 is turned on and is input to the base end of the first transistor Q1, The second transistor Q2 is turned on because a low level signal is applied to the base end of the second transistor Q2.

As the second transistor Q2 is turned on, a high level signal is applied to the base end of the third transistor Q3 to turn on the third transistor Q3.

As the third transistor Q3 is turned on, a direct-current voltage of -80 V outputted from the high-voltage generating part 10 is applied to the emitter terminal of the second transistor Q2, and the collector terminal of the CRT The control grid 20 of FIG.

Here, the resistor R10 is implemented as a resistive element having a very small resistance value, and a DC voltage of -80V outputted from the high voltage generating portion 10 is supplied almost directly to the control grid 20 of the CRT.

That is, when a high-level mute signal is output from the microcomputer 30 at the time of power on / off or mode conversion, the voltage of the control grid 20 input to the CRT increases from -60 V (at normal operation) to -80 V The electron emission is suppressed and the screen is entirely kept as it is.

Here, the operation of the charging unit 44 will be described. In the normal operation, since the third transistor Q3 is turned off, the capacitor C3 is charged by the power supply voltage Vcc.

When the power source is turned off, the power source voltage Vcc is not supplied. Therefore, energy between the both ends of the capacitor C3 is reversed by the principle of energy conservation so that the negative electrode potential of the capacitor C3 is changed to a lower negative potential (-) voltage of the control grid 20 becomes large, thereby weakening the spot.

When the microcomputer 30 applies a DC voltage signal having a variable level to the base end of the fifth transistor Q5, the operation of the brightness signal processor 50 is controlled according to the level of the brightness signal. The collector current of the fifth transistor Q5 is changed, and thus the base current of the sixth transistor Q6 is changed. Therefore, the current flowing through the resistor R17 varies depending on the level of the luminance signal.

Since the resistor R17 is connected in parallel with the resistors R8 and R9 of the voltage lower portion 41, the resistor R17 is connected to the control grid 20 of the CRT according to the magnitude of the current flowing through the resistor R17. The supplied current is changed. As a result, by adjusting the level of the luminance signal, the brightness of the screen can be adjusted by increasing or decreasing the control grid current supplied to the control grid 20 of the CRT.

Also, the cut-off determining unit 60 is connected between the first resistor R8 and the second resistor R9, and the fourth transistor Q4 is maintained in a turned-on state during normal operation. Unlike the case where the brightness signal processor 50 is operated by the microcomputer 30, the fourth resistor R13 is used as a sub-brightness adjustment terminal for adjusting the brightness externally by the operator .

As described above, the present invention has the effect of protecting the CRT by changing the negative voltage supplied to the control grid of the CRT when the mute operation, the power-off, or the luminance signal change.

Claims (6)

A high voltage generating unit 10 for rectifying the AC voltage generated from the flyback transformer FBT to a DC voltage and supplying it to the control grid 20 of the CRT; Outputs a first level mute signal during normal operation and then outputs a second level mute signal at a power on / off state or during a mode transition for a while, the second level being a level opposite to the first level, The CRT includes a microcomputer 30 for outputting a luminance signal of a direct current voltage. When the first level mute signal is input, the negative voltage outputted from the high voltage generating unit 10 is lowered, Voltage to the control grid 20 and supplies the negative voltage to the control grid 20 of the CRT when the mute signal of the second level is input to the control grid 20, A mute signal processing unit (40) for further boosting the voltage and supplying the voltage to the control grid (20) of the CRT; A luminance signal processing unit 50 for changing the magnitude of a negative voltage supplied to the control grid 20 of the CRT according to the luminance signal input from the microcomputer 30; And a cutoff determining unit 60 for blocking energy supplied from the high voltage generating unit 10, the mute signal processing unit 40 and the luminance signal processing unit 50 to the control grid 20 of the CRT, ) Of the CRT. The apparatus of claim 1, wherein the mute signal processing unit (40) comprises: a voltage lower portion (41) for lowering the supplied voltage; A switching driver (42) for receiving the mute signal and outputting a driving signal; (-) voltage is supplied to the control grid as it is, and a negative (-) voltage supplied in the off state is supplied to the CRT through the voltage lower part 41 A switching unit (43) for supplying the control grid (20); And a charging unit (44) for charging a constant voltage during normal operation and increasing the negative voltage of the control grid (20) by converting the energy between the opposite ends when the power is off, Protection device. The driving circuit according to claim 2, wherein the switching driver comprises: a first transistor having a base end connected to the mute signal, a collector connected to a power supply voltage Vcc and an emitter connected to ground; And a second transistor Q2 whose base end is connected in parallel between the power supply voltage Vcc and the collector terminal of the first transistor Q1 and whose emitter terminal is connected to the power supply voltage Vcc, The switching unit 43 has a base end connected to the collector terminal of the second transistor Q2 and a collector terminal connected to the control grid 20 of the CRT. An emitter terminal of the switching unit 43 is connected to the flyback transformer FBT, And a third transistor Q3 receiving a voltage. The voltage lower part (41) according to claim 3, wherein the voltage lower part (41) is connected in parallel between one end of the first resistor (R8) and the emitter end of the flyback transformer (FBT) One end of the resistor R9 is connected to the other end of the first resistor R8 and the other end of the second resistor R9 is connected to the collector terminal of the third transistor Q3 and the control grid 20 ) Of the CRT are connected in parallel. The CRT protecting device according to claim 3, wherein the charging unit (44) comprises a capacitor (C3) connected between a collector terminal and an emitter terminal of the third transistor (Q3). The apparatus of claim 4, wherein the luminance signal processor (50) comprises: a fifth transistor (Q5) having a base end for receiving a luminance signal from the microcomputer (30); And a collector terminal of the fifth transistor Q5 is connected to the control grid 20 of the CRT and an emitter terminal of the fifth transistor Q5 is connected to the flyback transformer FBT via the resistor R17, And a sixth transistor (Q6) connected in parallel between the lower part (41) of the capacitor.