Effect of the miller-capacitance during switching transients of IGBT and MOSFET

The feedback from the drain to the gate of MOSFET resp. from the collector to the gate of an IGBT during switching transients is described by the miller-capacitance. This is an appropriate approach for MOSFET, where a positive dvDG/dt leads to a positive current through the miller-capacitance. The aim of this paper is to explain, why during turn-off of a bipolar device like an IGBT, this is not always the case. A positive dv_CG/dt may lead to a negative current through the miller-capacitance. For a better understanding of the switching behaviour of the IGBT, it is helpful to take the time derivative of the electrical field peak as a measure for the current through the miller-capacitance.