Investigations on Averaging Mechanisms of Virtual Junction Temperature Determined by VCE (T) Method for IGBTs

In this article, the physical meaning of the virtual junction temperature determined by the VCE(T) method for insulated gate bipolar transistors (IGBTs), especially the averaging mechanisms, have been studied in depth to answer the question of which physically meaningful value of the chip is associated with the virtual junction temperature. A combination of theoretical analysis and electro-thermal simulation is performed to discuss the influence of temperature gradient on the virtual junction temperature, including vertical and lateral gradient. Furthermore, the averaging mechanisms of the virtual junction temperature are investigated and verified by effective experimental results. The results show that the virtual junction temperature is not a fixed value but a value related to the measurement current and is neither the area-weighted average temperature NOR the current-weighted average temperature, but it is in between. It provides guidance for understanding the virtual junction temperature in the measurement and defining the virtual junction temperature in the finite element model (FEM) simulation.