Power supply protection circuit utilizing a silicon controlled rectifier

Abstract

Abstract A control circuit for preventing the application of accelerating potential in excess of a predetermined maximum value to the cathode-ray picture tube of a television receiver. Positive polarity pulses amplitude-related to the applied accelerating potential are derived from the receiver horizontal deflection system and impressed across the emitter-base junction of a transistor. The base of this transistor is biased at a DC level such that the impressed pulses will exceed the breakdown potential of the junction when the accelerating potential exceeds its maximum value. When this occurs a control voltage is applied by the transistor to the control electrode of a silicon controlled rectifier (SCR) which has principal electrodes connected between the screen of the horizontal deflection system output tube and ground. This causes the SCR to conduct, substantially reducing the screen current applied to the output tube and hence the energy available for powering the receiver''s sweep-excited high voltage power supply, and preventing further generation of excessive accelerating potential. To prevent the receiver from being rendered inoperative by a transient overload condition, a capacitor couples pulses from the output circuit of the receiver vertical deflection system to the screen of the horizontal output tube to periodically reduce the quiescent current through the principal electrodes following an overvoltage condition to a value below the minimum holding current required to sustain conduction, thereby restoring the SCR to a nonconductive state and the high voltage power supply to an operative state. During a sustained overvoltage condition the control circuit causes the receiver to alternate between operative and nonoperative states, which ''''blinking'''' action on the receiver viewing screen effectively indicates a malfunction.

Inventors

• 👤 Kenneth Frizane

Bibliographic Details