KR19980017809A - CRT protection device - Google Patents

Abstract

The present invention relates to a CRT protection device, the device of the present invention, the high-voltage generator 10 for supplying a negative voltage (-) to the control grid 20 of the CRT; In the CRT equipped with a microcomputer 30 for outputting a luminance signal of a variable level, and outputs a mute signal of the first level during normal operation, and a mute signal of the second level when power on / off or mode conversion. When the mute signal of the first level is input, the negative voltage output from the high voltage generator 10 is dropped and supplied to the control grid 20. When the mute signal of the second level is received, the negative voltage is kept as it is. A mute signal processor 40 which supplies the control grid 20 and further boosts the negative voltage when the power is turned off and supplies the control grid 20 to the control grid 20; A luminance signal processor 50 for changing a magnitude of a negative voltage supplied to the control grid 20 by the luminance signal; And a cutoff determination unit 60 which cuts off the energy supplied to the control grid 20 from the high voltage generation unit 10, the mute signal processing unit 40, and the luminance signal processing unit 50 at a constant brightness boundary. In this configuration, the CRT can be protected by varying the negative voltage supplied to the control grid 20 during the mute operation, when the power is turned off or when the luminance signal is changed.

Description

An apparatus for protecting a CRT

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CRT protection device, and more particularly, to a CRT protection device configured to vary a negative voltage supplied to a control grid of a CRT during a mute operation, a power-off, or a variable luminance signal. .

In general, supplying the necessary voltage (rated voltage) to each monitor circuit at the time of power on / off or mode switching of the monitor causes an abnormality in each monitor circuit. After the circuit warms up, it is necessary to supply a ready voltage below the rated voltage and then supply the rated voltage for 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 for a while during power on / off or mode switching. At this moment, the control signal of the -DC voltage supplied to the CRT is stepped up from the cathode to the fluorescent film. It suppresses the amount of electrons emitted.

In general, a spot is a small light point generated by an electron beam colliding a fluorescent film of a CRT. When the monitor is turned on, the cathode of the electron gun is sufficiently heated to emit electrons. The spot is generated by hitting the fluorescent film.

In order for the screen to appear on the CRT, one spot must appear on the fluorescent film, and the spot must be deflected from side to side to make the raster and change the brightness of the spot as an image signal.

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

At this time, the larger the negative voltage is supplied to the control grid 20, the greater the force for suppressing the electron emission of the cathode, so that the amount of electrons colliding with the fluorescent film is reduced, thereby darkening the spot.

FIG. 1 is a block diagram of a general CRT protection device. Referring to FIG. 1, when the mute function of the general CRT protection device is performed, an AC voltage is output from a flyback transformer (FBT) when power is supplied to the monitor. Negative rectification (typically -80V).

In addition, the mute signal processing unit 40 lowers the DC voltage of -80V supplied from the high voltage generating unit 10 to about -60V during normal operation, that is, when the mute signal is at a low level, thereby controlling the CRT control grid 20. In the mode conversion, that is, when the mute signal becomes high, the DC voltage of -80 V supplied from the high voltage generator 10 is supplied to the control grid 20 of the CRT as it is.

Therefore, since the control grid 20 voltage input to the CRT increases from -60V to -80V when the mute function is performed, the screen is darkened by suppressing electron emission by that much.

In particular, when the monitor is powered off, since the charged cathode of the CRT has not yet cooled, the charge charged at a high pressure by the capacitance applied between the inner and outer conductive films of the water tube remains for a long time, It absorbs some of the electrons from the cathode, creating a spot.

However, since the deflection circuit is stopped 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 to generate a strong spot.

Therefore, when the power is turned off, only by adjusting the negative voltage of the control grid 20 using the mute function, the effect cannot be greatly seen. Therefore, the spot grid circuit 50 is additionally used to control the grid. The spot is weakened by further increasing the negative voltage supplied to (20).

In addition, the luminance signal of the DC voltage having a variable level is output from the microcomputer 30 at the request of the user, thereby controlling the brightness (brightness) of the screen by varying the control grid signal. In general, in the CRT, the 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 during mute operation, power off, or when the luminance signal is variable, and the circuit operation is also complicated.

Accordingly, the present invention has been made to solve the above problems, and the circuit implementation can be more easily implemented by varying the negative voltage supplied to the control grid of the CRT during mute operation, power off, or variable luminance signal. It is an object of the present invention to provide a CRT protection device adapted to protect the CRT.

CRT protection device of the present invention for achieving the above object, the high-voltage generator for rectifying the AC voltage generated from the flyback transformer to -DC voltage and supplying to the control grid of the CRT; Outputs the mute signal of the first level during normal operation, and outputs the mute signal of the second level which is inverse to the first level for a while during power on / off or mode switching, and the level is variable at the request of the user. In a CRT equipped with a microcomputer for outputting a luminance signal of a DC voltage, when a mute signal of the first level is input, a negative voltage output from the high voltage generator is dropped and supplied to the control grid of the CRT. When the mute signal of the second level is input, the negative voltage is supplied to the control grid of the CRT as it is, and when the power is turned off, the negative voltage is further boosted to supply the control grid of the CRT. A signal processor; A luminance signal processor for changing a magnitude of a negative voltage supplied to the control grid of the CRT by the luminance signal input from the microcomputer; And a cutoff determination unit which cuts off the energy supplied to the CRT control grid from the high voltage generating unit, the mute signal processing unit, and the luminance signal processing unit at a constant brightness boundary.

That is, the present invention is to protect the CRT by varying the negative voltage supplied to the control grid of the CRT during a mute operation, when the power is turned off, or when the luminance signal is changed.

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

2 is a circuit diagram illustrating a CRT protection device according to the present invention.

* Names of symbols for main parts of the drawings

10: high pressure generating unit 20: CRT

30: micom 40: mute signal processing unit

50: luminance signal processing unit 60: cutoff determination stage

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

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

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

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

2 is a circuit diagram illustrating a CRT protection device according to the present invention.

As shown in FIG. 2, the CRT protection apparatus according to the present invention includes a high voltage generator 10, a control grid 20 of a CRT, a microcomputer 30, a mute signal processor 40, and a luminance signal processor ( 50); And a cutoff determiner 60.

Here, the mute signal processor 40 includes: a voltage drop unit 41 for dropping the supplied voltage; A switching driver 42 which receives the mute signal and outputs a driving signal; When the driving signal is applied, the switching is turned on / off, and the negative voltage supplied when switching on is supplied to the control grid as it is, and the negative voltage supplied when off is supplied to the CRT through the voltage drop unit 41. A switching unit 43 for supplying to the control grid 20; It consists of a charging section 44 that charges a constant voltage in normal operation and converts the energy between both ends into a reverse potential when the power is turned off to increase the negative voltage of the control grid 20.

The switching driver 42 may include: a first transistor Q1 having a base terminal applied with the mute signal, a collector terminal connected to a power supply voltage Vcc, and an emitter terminal grounded; The base terminal is composed of a second transistor Q2 connected in parallel between the power supply voltage Vcc and the collector terminal of the first transistor Q1, and the emitter terminal is connected to the power supply voltage Vcc. The switching unit 43 has a base end connected to the collector end of the second transistor Q2, a collector end connected to the control grid 20 of the CRT, and an emitter end connected to a negative voltage from the flyback transformer FBT. A third transistor Q3 is supplied with a voltage.

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

On the other hand, 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 being connected to the control grid 20 of the CRT; A base terminal is connected to the collector terminal of the fifth transistor Q5, the collector terminal is connected to the control grid 20 of the CRT, and an emitter terminal is connected to the flyback transformer FBT and the voltage through the resistor R17. And a sixth transistor Q6 connected in parallel between the dropping portions 41, and the cutoff determiner 60 has an emitter terminal through the third resistor R12 and the fourth resistor R13. In parallel between the emitter terminal of the fifth transistor Q5 and the control grid 20 of the CRT, the collector terminal is connected to the first resistor R8, and the base terminal is connected to the second resistor R9. It is.

Then look at the operation and effect of the present invention configured as described above.

Referring to FIG. 2, first, the operation of the mute signal processor 40 according to the present invention will be described. First, when an AC voltage is output from the flyback transformer FBT by supplying power to the monitor, the resistor R1 and the diode D1 are used. Negative rectification through, and the rectified -DC voltage (typically -80V) is smoothed through the capacitor (C1).

In this case, when the mute signal processor 40 receives a mute signal having a first level (for example, a low level in the present embodiment) from the microcomputer 30 during normal operation, the first level mute signal is the first. As the first transistor Q1 is turned off by being input to the base terminal of the transistor Q1, the power supply voltage Vcc (eg, 120 V) is applied to the base terminal of the second transistor Q2 through the resistor R4. The second transistor Q2 is turned off, and a low level signal is applied to the base terminal of the third transistor Q3, thereby turning off the third transistor Q3.

As the third transistor Q3 is turned off, the DC voltage of -80V output from the high voltage generator 10 is dropped to about -60V through the resistors R8 and R9 to control the control grid 20 of the CRT. (The fourth transistor Q4 is constantly turned on in normal operation).

Then, during power on / off or mode switching, when the mute signal transitions to a second level (for example, a high level in this embodiment) that is inversely different from the first level for a few seconds, the mute signal of the second level is As the first transistor Q1 is turned on by being input to the base terminal of the first transistor Q1, the power supply voltage is applied to the emitter terminal of the first transistor Q1 through the resistors R3 and R2 and thus the collector stage. The low level signal is applied to the base terminal of the second transistor Q2 and the second transistor Q2 is turned on.

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

As the third transistor Q3 is turned on, a DC voltage of −80 V output from the high voltage generator 10 is applied to the emitter terminal of the second transistor Q2 and passes through the resistor R10 through the collector terminal CRT. Is supplied to the control grid 20.

Here, the resistor (R10) is implemented as a resistance element having a very small resistance value, the DC voltage of -80V output from the high-voltage generator 10 is almost supplied to the control grid 20 of the CRT.

That is, when a high level mute signal is output from the microcomputer 30 during power on / off or mode conversion, the voltage of the control grid 20 input to the CRT increases from -60V (normal operation) to -80V. The screen is darkened overall by suppressing electron emission.

In this case, referring to the operation of the charging unit 44, since the third transistor Q3 is turned off in the normal operation, the capacitor C3 is charged by the power supply voltage Vcc.

Then, when the power is turned off, the power supply voltage Vcc is not supplied, so that the energy between the both ends of the capacitor C3 is converted into a reverse potential by the principle of energy conservation, so that the negative potential portion of the capacitor C3 is changed to a lower negative potential. As a result, the negative voltage of the control grid 20 increases to weaken the spot.

Meanwhile, referring to the operation of the luminance signal processing unit 50, when the microcomputer 30 applies a luminance signal of a DC voltage having a variable level to the base terminal of the fifth transistor Q5, the microcomputer 30 applies the luminance signal according to the luminance signal level. The collector current of the fifth transistor Q5 changes, so that the base current of the sixth transistor Q6 changes. Therefore, the current flowing through the resistor R17 varies according to the level of the luminance signal.

At this time, since the resistor R17 is connected in parallel with the resistors R8 and R9 of the voltage drop unit 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 current supplied changes. 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.

In addition, the cutoff determiner 60 is connected between the first resistor R8 and the second resistor R9 so that the fourth transistor Q4 maintains a turn-on state during normal operation. Unlike the luminance signal processing unit 50 operated by the microcomputer 30, the fourth resistor R13 also serves as a sub-brightness adjusting terminal configured to adjust luminance externally by an operator. .

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

Claims (6)

A high voltage generator 10 for rectifying the AC voltage generated from the flyback transformer FBT to -DC voltage and supplying the CRT to the control grid 20 of the CRT; Outputs the mute signal of the first level during normal operation, and outputs the mute signal of the second level which is inverse to the first level for a while during power on / off or mode switching, and the level is variable at the request of the user. In a CRT equipped with a microcomputer 30 for outputting a luminance signal of a DC voltage, when the mute signal of the first level is input, the negative voltage output from the high voltage generator 10 is dropped to reduce the CRT. When supplied to the control grid 20, and receives the mute signal of the second level, the negative voltage is supplied to the control grid 20 of the CRT as it is, while the negative voltage is supplied when the power is turned off. A mute signal processor 40 for further boosting and supplying the voltage to the control grid 20 of the CRT; A luminance signal processor (50) for changing the magnitude of the negative voltage supplied to the control grid (20) of the CRT by the luminance signal input from the microcomputer (30); And a cutoff determiner 60 which cuts off energy supplied from the high voltage generator 10, the mute signal processor 40, and the luminance signal processor 50 to the control grid 20 of the CRT at a constant brightness. CRT protection device comprising a). 2. The mute signal processor (40) according to claim 1, further comprising: a voltage drop (41) for dropping the supplied voltage; A switching driver 42 which receives the mute signal and outputs a driving signal; When the driving signal is applied, the switching is turned on / off, and the negative voltage supplied when switching on is supplied to the control grid as it is, and the negative voltage supplied when off is supplied to the CRT through the voltage drop unit 41. A switching unit 43 for supplying to the control grid 20; CRT comprising a charging unit 44 which charges a predetermined voltage in normal operation and converts energy between both ends into a reverse potential when the power is turned off to increase the negative voltage of the control grid 20. Protection device. 3. The switching driver (42) according to claim 2, further comprising: a first transistor (Q1) having a base terminal applied with the mute signal, a collector terminal connected to a power supply voltage (Vcc), and an emitter terminal grounded; The base terminal is composed of a second transistor Q2 connected in parallel between the power supply voltage Vcc and the collector terminal of the first transistor Q1, and the emitter terminal is connected to the power supply voltage Vcc. The switching unit 43 has a base end connected to the collector end of the second transistor Q2, a collector end connected to the control grid 20 of the CRT, and an emitter end connected to a negative voltage from the flyback transformer FBT. A third transistor Q3 is supplied with a voltage. 4. The voltage drop part 41 of claim 3, wherein one end of the first resistor R8 is connected in parallel between the flyback transformer FBT and the emitter end of the third transistor Q3. 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. CRT protection device, characterized in that connected in parallel between). 4. The CRT protection device according to claim 3, wherein the charging unit (44) is composed of a capacitor (C3) connected between the collector terminal and the emitter terminal of the third transistor (Q3). 5. The luminance signal processor (50) according to claim 4, further comprising: a fifth transistor (Q5) whose base end receives a luminance signal from the microcomputer (30); A base terminal is connected to the collector terminal of the fifth transistor Q5, the collector terminal is connected to the control grid 20 of the CRT, and an emitter terminal is connected to the flyback transformer FBT and the voltage through the resistor R17. A CRT protection device comprising a sixth transistor (Q6) connected in parallel between the dropping portions (41).