HORIZONTAL SYNCHRONIZING CIRCUIT

摘要

PURPOSE:To prevent such a defective case where the X rays are continuously radiated through the surface of a picture tube in a continuous abnormal state by changing the output signal frequency of a horizontal oscillator by a 1st reference voltage and stopping the output of video signals by a 2nd reference voltage. CONSTITUTION:When the input voltage rises up to the level of the 1st reference voltage due to some fault, an overvoltage protecting circuit 6 cuts an AFC loop of a horizontal AFC circuit 1 and forcibly changes the oscillation frequency of a horizontal oscillation circuit 2 to perform a hold-down operation as conventional. If the input voltage continuously rises and reaches the level of the 2nd reference voltage, the circuit 6 performs a black-out operation to stop the output of a video signal processing circuit 7. The 2nd reference voltage is generated in the circuit 6 based on the 1st reference voltage and usually kept at a level slightly higher than the 1st reference voltage. Thus it is possible to prevent such a case where the X rays are continuously radiated through the surface of a picture tube in a continuous abnormal state. Then the effect and the danger can be eliminated to the human bodies.