CS242850B1 - Protective blackout circuit for screens - Google Patents

Abstract

The aim of the solution is to create a simple and reliable circuit with an immediate response. The stated aim is achieved by a circuit in which the output of the transformer of the final stage of the line decomposition is connected to the anode of a diode, the cathode of which is connected to the second input of a two-input circuit of the logical product negation type. The output of the image signal source is connected to the first input of a two-input circuit of the logical product negation type, the output of which is connected to the input of the image amplifier. The circuit can be used to turn off a light point on the screen of video monitors of television receivers and the like.

Description

The invention relates to a protective blackout circuit for video monitors, television sets and the like.

If the supply voltage or excitation pulses fail due to a fault, the screen shade must be darkened. Otherwise there is an undefined movement of the light point on the screen, where it affects the operator and results in gradual degradation of the screen. This phenomenon is due to the inertia of the incandescence, the residual space charge between the cathode and the control grid, and the capacitance of the screen holding the voltage, which accelerates the remaining electrons to form a slowly disappearing bright spot whose movement is no longer controlled by decomposition circuits.

To suppress this phenomenon, for example, large time constants are used in the circumference of the second grid to ensure the removal of the remaining charge. Another measure is protection by a brightness regulator connected between two voltage sources. In normal screen operation, the slider of the potentiometer is in such a position that the screen is lit by the nominal brightness. When the screen is turned off or a failure occurs, one voltage dissipates faster than the other. If the positive voltage persists for a longer time, the residual charge is led to the ground via the control grid. If the negative voltage is maintained for longer, the electron current is blocked. Another solution comprises a timing circuit with a capacitor charged by pulses from decomposition circuits, the output of which via a switch controls either the screen or the video amplifier directly.

These measures have a common drawback in the use of relatively large capacitors, which slow down the response speed and do not contribute to long-term reliability. In addition, there is a need for a variety of other passive and active components that complicate the entire display screen assembly.

- 2'242 850

These disadvantages are eliminated by the connection of the protective screen blanking circuit according to the invention, which is based on the fact that the output of the line decomposition output stage transformer is connected to the anode of the diode whose cathode is connected to the second input of the dual input logical product type. the first input of a dual-input logic product, the output of which is connected to the input of the video amplifier.

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The advantage of wiring the protective screen dimming circuit according to the invention is its simplicity and reliability, as well as its immediate response.

An example of a protective blanking circuit for a screen according to the invention is shown in the attached drawing, in which Fig. 1 is a circuit diagram and Fig. 2 is a timing diagram of the signals S1, S2, S3 and OS.

The output 01 of the line decomposition output stage transformer 1 for the signal S1 is connected to the anode of a diode 5, the cathode of which is connected both to the input 61 of the filter cell 6 whose output 06 is connected to zero potential. signal S2. The output 02 of the video signal source 2 OS is connected to the first input of a dual-input logic product 3, whose output for the signal S3 is connected to the input 41 of the video amplifier 4. The output 04 of the video amplifier 4 is connected to the input 71 of the screen 7.

The signal S1, which is the pulse voltage from the output 01 of the transformer of the final decomposition stage 1, is converted by a diode 5 to a signal S2. The filter element 6 removes unwanted oscillations on the diode 5. In the two-input circuit 3 of the logical product type, the product of this signal S2 is generated with the video signal OS. The resulting signal S3, after amplification in the video amplifier 4, is applied to the screen 7. If the signal S1 is generated when the screen is turned off or in the breakdown circuit, the signal S3 cannot appear at the output 04 of the video amplifier 4 and the screen 7 is dimmed. Also, at the time of the electron beam reversal, the screen 7 is dimmed. The activity of the wiring is further evident from the time

- 3 242 850 of the diagram of Fig. 2, where δΒ means the active run and ZB is the reverse run of the electron beam of the screen 7.

The invention can be used to turn off the light spot on the screen of the video monitors of television sets and the like.

Claims (1)

BACKGROUND OF THE INVENTION Protective blackout circuitry for displays characterized in that the output (01) of the transformer (1) of the final decomposition stage is connected to the anode of the diode (5), the cathode of which is connected to the second input of the dual input The video signal source (2) is connected to the first input of a dual-input logic product (3) whose output is connected to the video amplifier (4) input (41).