Malfunction detecting apparatus for use in a CRT deflection circuit

TLDR: In this article, a flyback transformer is connected to a resonant capacitor and is driven by a switching device synchronized with horizontal scanning pulses so that flyback pulses are produced during the normal retrace intervals in the horizontal deflection.

Abstract: Apparatus is provided for preventing the generation of an excessively high voltage by the high voltage circuit of a CRT device, such as a television receiver, thereby avoiding the danger of producing injurious X-ray radiation and further minimizing the potential fire hazard attributed to such an excessively high voltage. A flyback transformer is connected to a resonant capacitor and is driven by a switching device synchronized with horizontal scanning pulses so that flyback pulses are produced during the normal retrace intervals in the horizontal deflection. A relatively low voltage power supply is coupled to the switching device to apply an operating voltage thereto. A first detecting circuit is coupled to the flyback transformer for detecting a high frequency component included in the flyback pulses in the event of a malfunction of the resonant capacitor, such as a disconnection of that capacitor, which high frequency component causes an excessively high voltage to be produced by the high voltage circuit. A second detecting circuit is coupled to the flyback transformer for detecting a high flyback pulse level that is produced when the operating voltage applied by the low voltage power supply exceeds a predetermined level. In the event that the first detecting circuit detects the presence of a high frequency component or the second detecting circuit detects a high flyback pulse level, a switch is actuated to control the CRT deflection circuit, thereby reducing the level of the flyback pulses, and thus the level of the high voltage produced by the high voltage circuit.