Improved DC-modelling of high current bipolar transistors for accurate converter simulation

The modeling of bipolar transistors with current ratings from 200 A to 1000 A is considered. An approach based on the physical mechanisms in the device is used in contrast to the many curve-fitting approaches found in this field. It is shown that sufficient static modeling can be achieved by a minimum number of parameters that are easily determined experimentally. Existing models for low-current devices, namely, the Gummel-Poon, Ebers-Moll/Shockley, and Hower models, are examined, and a survey of the literature is given. The fundamental assumptions of high-current modeling are derived, the second-order effects are examined, and the dominant mechanisms for DC operation are derived by a detailed experimental investigation. It is shown that the Hower model is the most suitable approach for high-current bipolar transistors in quasi-saturation. The findings of the study are incorporated into an improved model and incorporated in the SPICE network simulation program. It is shown by comparison of simulation and experiment that the proposed approach models the behavior of power devices in switches adequately for converter simulation over a wide range of operating conditions.<>