Deutsche Thomson-brandt Gmbh

Eduard Lohmuller

Uwe Hartmann

Fritz Ohnemus

A circuit for demagnetizing a mask in a color picture tube of a television receiver, in which a resistor with positive temperature coefficient is applied to the input alternating current when the receiver is turned on. A bridge rectifier is connected with one terminal, to a first pole of the alternating current source, via the demagnetizing coil that is mounted on the picture tube, and the resistor. The bridge rectifier has another terminal connected to a second pole of the alternating current source. A variable electronic switch interconnects the direct-current output terminals of the bridge rectifier. The variable electronic switch is controlled to continuously decrease current flowing through the demagnetizing coil to zero. For this purpose, a controlling voltage is obtained from a winding in a horizontal-frequency synchronized power-intake stage by flyback rectification. A feedback circuit is connected to a delay network and to the variable electronic switch for opening the latter completely after a time interval determined by the delay network.

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Villingen-Schwenningen, Germany

Eduard Lohmuller