High-Voltage IGBT turn-off at transition from overcurrent to desaturation

Abstract

The turn-off capability of a power semiconductor is normally given by the datasheet with test conditions. The RBSOA (Reverse Bias Safe Operation Area) diagram limits the collector-emitter peak voltage and maximum turn-off current [1]. As mentioned in the early literature and many datasheets of IGBT power modules, the current which can be turned off is limited to twice the nominal current, in the between this and short circuit it is forbidden to turn off the device [2]. In this paper, the turn-off behaviour of HV- IGBTs at the transition from overcurrent to desaturation is investigated with a 2D half-cell model in Synopsys TCAD as well as with single chip measurements. This article focuses on the classification of the turn-off process near the VCE desaturation, with respect to the plasma- and electric field distribution, dynamic avalanche, as well as electric field peaks which occur during this process. It shows that the IGBT can be operated in this former forbidden region successfully, and a beginning desaturation releases dynamic avalanche.