Low cast chopper inverter power supply and gating circuit therefor

Abstract

A metal based cookware induction heating apparatus having an improved power supply and control circuit comprised of a chopper inverter including a gate controlled power thyristor coupled to and supplying an induction heating coil with periodic energization currents. A full wave rectifier supplies rectified, unfiltered, unidirectional high voltage excitation potential to the chopper inverter which converts the excitation potential to a comparatively high frequency of the order of 20 kilohertz for supply to the induction heating coil. A gating circuit is provided for driving the chopper inverter directly from the rectified high voltage excitation potential supplied by the rectifier. The gating circuit includes an additional low voltage, direct current excitation potential connected to supply to a timing circuit charging capacitor. A voltage responsive switch such as a SUS or PUT or their equivalents is rendered conductive upon the timing circuit reaching a present value and in turn rendered conductive a constant current high voltage switching transistor connected in series with the primary winding of a pulse transformer across the output of the additional low voltage derived from the main full wave rectifier. The pulse transformer in turn has its secondary winding connected to the control gate of the power thyristor included in the chopper inverter.