| Abstract |
At high switching speeds silicon pin-diodes can show a significant forward recovery voltage, which appears as a reverse voltage over the anti-parallel IGBT. The avalanche breakdown of the IGBT floods its base-region with electron-hole-plasma, which is extracted when the diode is turned-off again after a while and contributes to the diode's reverse recovery peak. This effect increases the losses and endangers the IGBT because it is designed neither for a reverse avalanche breakdown nor for a reverse recovery. This work investigates the turn-on behaviour of silicon pin-diodes and SiC-Schottky-diodes (SBD) and their influence on the IGBT by means of measurements and mixed-mode simulations. The measurements were done on a 1000 A, 1700 V PrimePACK3 half-bridge module and on a special set-up with a discrete IGBT and a discrete diode (both with a rating of 20 A, 1200 V) to investigate the interaction between the two devices. At the end it turns out that the IGBT is indeed doing a reverse recovery, if it had been flooded during diode turn-on. The effect is rather small with the investigated 1200 V and 1700 V devices but it is much more severe for higher voltage classes. Using a unipolar SiC-Schottky-diode removes the turn-on overvoltage (but not the inevitable inductive component) and the stress on the IGBT. This way, the switching speed can be further increased and losses can be reduced. |
