Dynamics of IGBT performance in hard- and soft-switching converters

This paper reports on the physics of IGBT switching dynamics in soft- and hard-switching conditions. Mixed device and circuit simulations were used to study the carrier dynamics during turn-on and turn-off. It is shown that di/dt-dependent turn-on voltage spike results from high drift-region resistivity in the low-level injection regime. Beyond the voltage spike, dynamic forward voltage saturation occurs because of high-level injection. These two effects cause lead to conductivity modulation lag during turn-on under ZVS conditions. During turn-off, dv/dt-dependent elevated tail-current “bump” results from the interaction between electric field and carrier recombination mechanisms. The turn-on and turn-off characteristics are measured under various boundary conditions and an excellent agreement with the simulated results is obtained