Operation of an IGBT in a self-clamped inductive switching circuit (SCIS) for automotive ignition

IGBTs designed for automotive applications can be subjected to high levels of electro-thermal stress due to abnormal conditions, such as an open secondary. These stress conditions are fundamentally different to those seen by an IGBT in the more common shorted load motor drive applications. In the ignition application, the peak IGBT collector current is much lower and is unique to each ignition application. The IGBT current during turn-off is controlled by the di/dt set by the coil inductance and the interaction during the open secondary condition. Until the current falls to a near zero value, the IGBT's internal gate signal is present. This gate level is set by the IGBT transconductance. The purpose of this paper is to explain the physics of the operation of the IGBT under these stress conditions in the ignition application, both through simulation and experiment. The mechanism of IGBT failure is described and a technique to predict device capability through simulation is presented.