Soft switching involves turning the semiconductor device on or off with min
imal switching stress. Zero voltage switching (ZVS) and zero current switch
ing (ZCS) are the two most popular variants of soft switching schemes. The
turn-off performance of insulated gate bipolar transistors (IGBT's) under Z
VS and ZCS environments is critically evaluated in this paper. It is shown
that the turn-off mechanism under ZVS and ZCS conditions is dissimilar. Cha
rge removal from the drift region during ZVS turn-off is mainly due to carr
ier 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 importa
nt 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 soft-switching environ
ment.