Transient junction temperature estimation of IGBT using improved thermal model

Insulated gate bipolar transistors (IGBTs) under some extreme conditions, such as the variation of the load or outside disturbance, will cause a transient junction temperature rise. This temperature step is one of the major causes of IGBT failure. However, in the traditional Cauer-type thermal model, the temperature of each layer inside IGBT is assumed to be well distributed. This assumption will impair the accuracy of the thermal analysis. In this paper, an improved thermal model that can accurately predict the junction temperature under transient temperature rise is proposed, based on the accurate structure description of IGBT with an active volume. The theoretical expression of the temperature derived from the improved model is verified by finite element analysis (FEA). The outcome of the proposed model can provide a design reference for short circuit protection and failure analysis.