Some effects of base current on transistor switching and reverse-bias second breakdown

Some experimental observations of the switching characteristics and second breakdown susceptibility of high-voltage, fast-switching power transistors are discussed. A unique test circuit is described which permits devices to be taken into reverse-bias second breakdown many times with little or no apparent degradation. Evidence for the constriction of emitter current to the centers of the emitter fingers during the time associated with the extraction of stored charge is presented, three modes of reverse-bias second breakdown are shown, and reverse-bias safe-operating-area limits which have been nondestructively determined are shown.