SWITCHING DYNAMICS OF IGBTS IN SOFT-SWITCHING CONVERTERS

Next generation of power semiconductor devices will be designed and op timized to meet the specific application requirements. Mixed-mode simu lations are used to study the carrier dynamics in punch-through and no npunch-through Insulated Gate Bipolar Transistor (IGBT) structures dur ing soft- and hard-switching conditions. The simulation results are sh own to qualitatively predict the measured bump in the tail current wit h varying output dv/dt conditions and excessive forward conduction vol tage under varying di/dt conditions. A new physical effect termed ''co nductivity modulation lag'' is shown to occur during turn-on under sof t-switching conditions. This mechanism is caused by the fact that mino rity carrier injection into the base of the bipolar transistor signifi cantly lags behind the rate at which drift region conductivity can be modulated. The proposed phenomenon leads to an inductive effect that r esults in dynamic voltage saturation during turn-on and causes excessi ve forward voltage drop.