Internal dynamics of IGBT under zero-voltage and zero-current switching conditions

Soft switching involves turning the semiconductor device on or off with minimal switching stress. Zero voltage switching (ZVS) and zero current switching (ZCS) are the two most popular variants of soft switching schemes. The turn-off performance of insulated gate bipolar transistors (IGBT's) under ZVS and ZCS environments is critically evaluated in this paper. It is shown that the turn-off mechanism under ZVS and ZCS conditions is dissimilar. Charge removal from the drift region during ZVS turn-off is mainly due to carrier sweep-out and recombination. On the other hand, charge removal through the channel during the phase of no device current is shown to be an important mechanism governing the magnitude and extent of the current tail during ZCS turn-off. This also results in significantly reduced turn-off losses of IGBT in ZCS as compared to ZVS. Improved understanding of internal carrier dynamics will lead to better utilization of IGBT in a soft-switching environment.