KR19990040152U - Spot removal circuit - Google Patents

Abstract

The disclosed spot elimination circuit applies a negative high voltage to the first grid in accordance with the spot elimination signal generated due to the power supply of the cathode ray tube image display device or the supply of horizontal and vertical synchronization signals due to a mode change. It is about a circuit that removes spots that appear on the screen.

The spot elimination circuit according to the present invention outputs a low potential voltage when both the horizontal synchronizing signal and the vertical synchronizing signal are input to the cathode ray tube image display device, and the output terminal is opened when none of the horizontal synchronizing signal or the vertical synchronizing signal is input. When the output of the spot removal signal generator and the spot removal signal generator are low voltage, the negative high voltage applied from the outside is distributed and applied to the first grid of the cathode ray tube, and the output terminal of the spot removal signal generator is opened. The first grid voltage control unit may be configured to apply to the first grid without distributing a negative high voltage applied from the outside.

Therefore, the present invention has an advantage that the mounting space on the printed circuit board can be reduced by simply configuring the spot elimination circuit and reducing the number of components in the manufacture of the actual circuit.

Description

Spot removal circuit

The present invention relates to a spot removing circuit of a video display device using a cathode ray tube (CRT).

More specifically, in a video display device such as a computer monitor and a television receiver using a cathode ray tube, when the device is turned off and both horizontal and vertical sync signals are not input, the horizontal as the mode is changed. Alternatively, a spot that appears on the screen can be removed by using a circuit that applies a negative high voltage to the first grid G1 as a suppression grid according to a spot removal signal generated when a vertical synchronization signal is not input. A spot killer circuit is disclosed.

FIG. 1A is a view for explaining a capacitor formed in a cathode ray tube. In general, a cathode ray tube is coated with conductive films 2 and 3 in which graphite and the like are purified on the inner and outer surfaces of the panel 1 as shown. Between the conductive films 2 and 3, a capacitor having a glass of the panel 1 as a dielectric is formed.

FIG. 1B shows a capacitor formed as described above as the equivalent circuit diagram of FIG. 1.

When the cathode ray tube of the image display device operates, a positive high voltage (+ B) is applied to the conductive layer 2 inside the panel 1, and the capacitor is charged with a positive high voltage (+ B).

In this state, when the power of the image display device is turned off, extra heat remains in the heater of the cathode ray tube, so that hot electrons continue to be emitted from the cathode, and the high voltage (+ B) charged in the capacitor formed between the conductive films 2 and 3 is maintained. Is accelerated by

On the other hand, due to the interruption of the input of the horizontal and vertical synchronization signals due to the power off, the deflection current to the horizontal and vertical deflection coils no longer flows, and in this state, the electron beam caused by the hot electrons is negative in the cathode ray tube. It hits only the central part of the fluorescent film and generates spots and appears on the screen.

At this time, if the discharge time of the high voltage charged in the capacitor formed between the conductive films 2 and 3 is long, the time for which the spot remains on the fluorescent screen is also long, and since the strong stimulus is continued to the fluorescent screen, the screen of the cathode ray tube image display device Burst noise is not only generated on the phase, but the fluorescent film itself is also deteriorated to shorten the lifespan.

As described above, the spot is powered off of the video display device so that both horizontal and vertical synchronization signals are not input, as well as a display power management system (DPMS) proposed by the video electronics standard association (VESA) of the United States. As the mode of the video display device is changed according to the < RTI ID = 0.0 >

The reason for this is that the horizontal and vertical deflections are also changed even when the mode of the video display device is changed to the stand-by state or the suspend state in order to save power, as the power management system regulations intended. At the same time, the hot electrons due to the heat of the heater are continuously released.

Accordingly, the spot display circuit is provided in the video display device using the cathode ray tube so that the spot as described above does not occur when the power is turned off or the mode is changed.

2 is a circuit diagram showing an example of such a conventional spot removing circuit.

As shown, when power is applied to the image display device, the transistor Q21 is turned on and remains on as long as the driving power + VE is normally supplied. Not shown for supplying power (+ VE) to the polarity capacitor C21 and resistor R21 connected in parallel between the base terminal and ground and to the emitter terminal of transistor Q21 via another resistor R22. A polarity capacitor C22 connected to the output terminal of the power supply source, a collector terminal of the transistor Q21, and a negative high voltage (-B) generation source (not shown) to distribute the voltages at both ends to form a suppression grid. A plurality of resistors R23, R24, and R25 are applied to one grid G1.

The operation of the conventional spot removal circuit configured as described above is as follows.

First, when the image display device operates normally and the power is supplied to the transistor Q21 normally, the transistor Q21 is turned on to form a current flow from the power source (+ VE) to the negative high voltage (-B) source. do.

With this current flow, the voltage between the power supply (+ VE) and the negative high voltage (-B), typically about -210 [V], is divided by resistors (R23) (R24) and (R25). The potential of the connection point of the resistors R23 and R24 is applied to the first grid. In this case, the distribution voltage applied to the first grid is about -60 [V], so that the cathode ray tube image display device normally displays the video signal on the screen. It does not matter in display.

When the transistor Q21 is turned on and operated as described above, the capacitor C21 connected to the base terminal of the transistor Q21 is charged with a voltage corresponding to the voltage difference VEB between the emitter terminal and the base terminal. The capacitor C22 connected to the output terminal of the illustrated power supply is charged with the output voltage + VE of the power supply.

If the cathode ray tube image display device is turned off or the mode is changed during the normal operation as described above, the power supply (+ VE) supplied to the transistor Q21 is cut off and the transistor Q21 stops its operation. A negative high voltage (-B) across the grid of resistor R25 is applied directly through resistor R24.

In this case, a voltage of -210 [V] applied to the first grid forms a strong negative field in the first grid such that hot electrons emitted from the cathode of the cathode ray tube cannot pass through, so the hot electrons are formed in the cathode ray tube. It is impossible to reach the fluorescent film of, and eventually no spot appears on the screen of the cathode ray tube video display device.

Here, as described above, the time point at which the spot removing circuit operates normally and the spot is removed coincides with the time point when the transistor Q21 is turned off. In FIG. 2, a capacitor connected to the base of the transistor Q21 is used. The C21 and the resistor R21 shorten the turn-off time of the transistor Q21.

That is, when there is no capacitor C21 and resistor R21 connected to the base of transistor Q21, the voltage + VE supplied to transistor Q21 is stabilized to a constant value by being connected to an output terminal of a power supply not shown. The transistor Q21 is not turned off until the voltage (+ VE) charged in the capacitor C22 to be discharged is equal to or less than the voltage difference VEB between the emitter and the base of the transistor Q21. There is a time after which the spot will appear without being removed even if the device is powered off.

However, as shown in Fig. 2, if the discharge circuit composed of the capacitor C21 and the resistor R21, which preferably has a discharge time much larger than the discharge time of the above-described capacitor C22, is connected to the base terminal of the transistor Q21, When the transistor Q21 is in the on state, the capacitor C21 is charged with the above-described voltage, and thus the power of the image display device is turned off, so that the capacitor C22 is charged between the capacitor C21 and the emitter and base of the transistor Q21. When discharged to the moment having the same voltage as the sum of the voltage difference VEB, the reverse voltage is applied between the base of the transistor Q21 and the emitter and turned off.

At this time, the turn-off time of the transistor Q21 is determined according to the difference between the magnitude of the voltage charged in the capacitor C21 connected to the base terminal and the time when the two capacitors C21 and C22 are discharged. These are related to the capacitance of the capacitor constituting the spot elimination circuit and the resistance values related to charge and discharge.

Since the spot elimination circuit of the conventional video display device having the above-described configuration and operation is determined by whether or not power is supplied to a predetermined switching circuit of the cathode ray tube image display device, the switching transistor and voltage A large number of components such as a charge / discharge capacitor and a plurality of resistors were required. This causes a lot of mounting space on the printed circuit board, which limits the miniaturization of the image display device.

Accordingly, an object of the present invention is to provide a simple circuit configuration that operates by supplying horizontal and vertical synchronization signals instead of power supplied to a predetermined circuit of a cathode ray tube video display device. The present invention provides a spot removing circuit capable of removing spots as in the prior art.

1A is a view for explaining a capacitor formed in the cathode ray tube,

1B is an equivalent circuit diagram of FIG. 1;

2 is a circuit diagram showing an example of a conventional spot removing circuit;

3 is a circuit diagram illustrating an embodiment of a spot removing circuit according to the present invention.

* Explanation of symbols for main parts of the drawings

10. spot removal signal generator 20: first grid voltage controller

21: reverse current blocking element 22: voltage divider

D31: diodes R31, R32: resistor

Features of the spot elimination circuit according to the present invention for achieving the above object is to output a low potential voltage when both the horizontal synchronizing signal and the vertical synchronizing signal is input to the cathode ray tube image display device, and either the horizontal synchronizing signal or the vertical synchronizing signal If no signal is input, the spot elimination signal generator which opens the output terminal and the spot elimination signal generator are divided into a negative high voltage applied from the outside and applied to the first grid of the cathode ray tube when the output of the spot elimination signal generator is low potential. When the output terminal of the spot elimination signal generator is opened, the first grid voltage controller is configured to apply the negative grid high voltage to the first grid without distributing a negative high voltage.

Hereinafter, a preferred embodiment of the spot removing circuit according to the present invention will be described in detail with reference to FIG.

3 is a circuit diagram illustrating an embodiment of a spot removing circuit according to the present invention.

As shown, the spot elimination circuit according to the present invention applied to the cathode ray tube image display device includes a spot elimination signal generator 10 for outputting different states according to whether the horizontal synchronizing signal and the vertical synchronizing signal are input, and the spot elimination circuit; The first grid voltage controller 20 is configured to supply the first grid with different voltages according to the output state of the signal generator 10.

Here, the first grid voltage control unit 20 is connected in series with the spot elimination signal generator 10 again to block the current flowing into the spot elimination signal generator 10 and the reverse current blocking element 21 and the reverse. And a voltage divider 22 which is connected in series with the current blocking element 21 and outputs a part of the negative high voltage (-B) applied from a negative high voltage source (not shown).

The operation of the spot removing circuit according to the present invention configured as described above is as follows.

First, when the cathode ray tube image display device is normally operated and both the horizontal synchronizing signal and the vertical synchronizing signal are input, the spot removing signal generator 10 maintains a low potential voltage, that is, a ground potential.

In this case, a current flow is formed from the output terminal of the spot elimination signal generator 10 to the negative high voltage generation source (not shown) via the reverse current blocking device 21 and the voltage divider 22, and the reverse current blocking. The voltage between the output terminal of the element 21 and the negative high voltage (-B) generated from the negative high voltage source is distributed by the voltage divider 22 to output the voltage of the first grid control unit 20. (Node A).

Here, the spot elimination signal generator 10 is generally preferably constituted by a microcomputer or a digital logic circuit, and a flyback transformer (FBT) is typically used as a source of negative high voltage (not shown). The voltage generated from this and supplied to the voltage divider 22 is about -210 [V].

At this time, the distribution voltage applied from the node A to the first grid is about -60 [V], so that the video display device maintains a potential that is not a problem in displaying a video signal on a screen normally.

As described above, it is possible to use the diode D31 as the reverse current blocking device 21, which is caused by reverse current flowing from the first grid or the negative high voltage source to the spot removing signal generator 10 to remove spots. The circuit of the signal generator 10 is prevented from being damaged.

In addition, the voltage divider 22 may be simply configured with a plurality of resistors R31 and R32, and the voltage of the node A supplied to the first grid is a voltage applied to the connection point of the resistors R31 and R32. .

However, when the cathode ray tube image display apparatus is turned off or the mode is changed, the spot elimination signal generator 10 does not input either the horizontal synchronizing signal or the vertical synchronizing signal, or both of them.

In this case, the output terminal of the spot elimination signal generator 10 maintains an open state as if the switch is open, so that the current flows from the output terminal to the reverse current interruption element 21 and the voltage divider 22. It will not form.

Thus, a negative high voltage of about -210 [V] applied from a negative high voltage source is directly applied to the first grid without being distributed by the voltage divider 22.

When a negative high voltage is applied to the first grid, hot electrons emitted from the cathode of the cathode ray tube cannot reach the fluorescent film because a strong negative electron field is formed in the first grid. The spots do not appear on the screen of the video display device because it is impossible.

As described above, according to the spot elimination circuit according to the present invention, a negative high voltage is generated according to the spot elimination signal generated due to supply of horizontal and vertical synchronizing signals according to power-off or mode change of the cathode ray tube image display device. By using a circuit that is applied to the first grid as it is, it is possible to simply configure the spot elimination circuit, there is an effect that can reduce the mounting space on the printed circuit board by reducing the number of parts in the production of the actual circuit.

Claims (4)

A spot elimination signal generator for outputting a low potential voltage when both the horizontal synchronizing signal and the vertical synchronizing signal are input, and opening the output terminal when no signal is input either the horizontal synchronizing signal or the vertical synchronizing signal; And If the output of the spot elimination signal generator is a low potential voltage, a negative high voltage applied from the outside is distributed and applied to the first grid of the cathode ray tube, and when the output terminal of the spot elimination signal generator is opened, the sound is applied from the outside. And a first grid voltage controller for applying the high voltage of (-) to the first grid without distributing the negative voltage. The apparatus of claim 1, wherein the first grid voltage controller comprises: a; A reverse current blocking device connected to an output terminal of the spot elimination signal generator to block a current flow from a first grid or a negative high voltage source to the spot elimination signal generator; And A voltage distribution in which the output voltage is applied to the first grid from the node where the voltage is distributed and is divided between the output terminal of the spot removing signal generator and the negative high voltage applied from the outside in series with the reverse current blocking device Spot removal circuit, characterized in that consisting of. The method of claim 2, wherein the reverse current blocking device; And a diode having an anode connected to the output terminal of the spot removing signal generator. 3. The apparatus of claim 2, wherein the voltage divider; Spot removal circuit, characterized in that composed of two or more resistive elements.