Conductivity modulation lag during IGBT turn on in resonant converter applications

Abstract

A novel physical mechanism is identified in the IGBT t u n on waveforms when switched in resonant converter applications. Dynamic saturation of the forward voltage drop Vce has been observed in excess of 1OV followed by voltage spikes under varying di/dt switching conditions. This value of Vce is far in excess of that due to inductance caused by the package and module substrate assembly. The additional di/dt induced voltage results from the inductive effect within the intrinsic device. As the device is being turned on, the rate of conductivity modulation of the drift region lags behind the rate at which the excess carriers are removed. Computer simulations using an advanced 2D mixed-mode circuit simulator suggest significant. amount of drift region " conductivity modulation lag 'I. In this simulator, 2D device carrier dynamics is calculated in an actual circuit switching environment, and thus, allows for the study of plasma spreading as the circuit boundary conditions are changed. This mechanism results in excessive turn on power loss in fast-switching IGBT's where device speed is increased using carrier lifetime killers. A circuit simulation model is developed that accurately predicts the turn on waveforms.