The Equivalent Electron Density Concept for Static and Dynamic Modeling of the IGBT Base in Soft- and Hard-Switching Applications

The transient and static behavior of an insulated gate bipolar transistor (IGBT) are analyzed through finite elements simulations and physically based equations. The standard model using a bipolar transistor driven by a MOSFET is abandoned for three partial voltage drops in series, each with its specific static and dynamic behavior. One voltage drop on the internal MOSFET, one on the base and one on the collector-base junction. It is found that the dynamic model can be drastically simplified by focusing on the equivalent electron density. This takes into account the most important phenomena related to the carrier mobilities, necessary for an accurate transient modeling. The specific behavior of the gate-collector capacitance in soft switching conditions is discussed. An equation set based on semiconductor physics is developed to determine the static operating points for each contribution. The importance of the minority carriers transit time in soft switching conditions is then shown. The similarity observed between the waveforms obtained through a finite element simulation and the waveforms obtained using the developed IGBT model within various external structures validates the proposed approach.