LOAD RESPONSIVE TRIGGER INTERVAL CONTROL

摘要

An induction heating apparatus of the invention is provided with a pair of inversely parallel connected thyristors which receives power from a low frequency energy source. Depending on the polarity of the source voltage, one of the thyristors is triggered into conduction by a control pulse generated in delayed response to a sensed forward bias potential at its anode for the purpose of supplying a forward current to a commutating circuit which is tuned to a high frequency in the ultrasonic range, whereupon a backward current is generated. The backward current is commutated through the other thyristor to complete a high frequency oscillation. A detector is provided to detect when the magnitude of the backward commutating current reaches a predetermined value for the purpose of terminating the trigger control pulse. The control pulses are supplied simultaneously to both thyristors through a pulse transformer which upon termination of the control pulse generates a counterelectromotive force which negatively biases the thyristor which has been conducting during the first half-cycle of each complete oscillation to reduce its turn-off time.