Improved capacitance model for power bipolar transistor turn-off performance

High voltage bipolar transistors are widely employed in many power supplies and most self-oscillating electronic ballasts for voltage applications up to 600 V. At the time of turn-off, these devices show significant storage time and fall time. This paper presents a new model to predict the fall time performance of power bipolar transistors. This is achieved by redefining the effective depletion capacitance to account for stored charge in the drift region of a power bipolar transistor in high level injection. The authenticity of the model is tested under various hard and soft switching load conditions. The model will enable better simulation of bipolar transistor turn-off characteristics in applications such as electronic lamp ballasts