Degaussing circuit for color television receivers

Abstract

A color television receiver having degaussing coil means which are energizable by an alternating current source and which are disposed in demagnetizing relation to magnetically permeable materials in receiver components such as the receiver picture tube is shown to include resistor means of positive temperature coefficient of resistivity in series with the degaussing coil means. The resistor means are self-heating when energized and display progressively increasing resistance as resistor temperature increases, the resistor means further displaying a sharp or anomolous increase in resistance when resistor temperature increases to a selected level. Preferably, relay means responsive to this increase in temperature of the resistor are connected in parallel with the degaussing coil means to shunt the degaussing coil means as resistor temperature increases to said selected level. The receiver circuit is arranged so that each actuation of the receiver from a cold start energizes the degaussing coil and resistor means to establish a magnetic field, subsequent heating of the resistor means progressively reducing degaussing coil current to reduce the magnetic field to substantially zero in a cyclical manner, thereby to demagnetize the receiver picture tube. Where used, the relay means respond to increase in resistor temperature to said selected level to shunt the degaussing coil means after the picture tube is demagnetized. A relay which incorporates the resistor means, relay contact means movable in response to resistor temperature, and appropriate terminals for connecting the relay in a television receiver circuit is also shown.