IGBT turn-off losses for hard switching and with capacitive snubbers

The authors present measured turn-off losses in IGBTs (insulated-gate bipolar transistors) from six different manufacturers. The rated breakdown-voltage and on-state current are 600 V and 75 A, respectively, for all transistors tested, except the IR-transistor which has 55 A as rate current. Hard switching and switching with a capacitive turn-off snubber are analyzed, both at 25 degrees C and 125 degrees C. The influence of variations in the gate resistance is covered. Conclusions from a similar set of measurements on 1000-1200 V IGBTs are also given. The loss reduction when using a turn-off snubber is larger than expected from experience with bipolar junction transistors. This is mainly due to the fact that the first part of the current fall time until the current tail is reached is shorter when a capacitive snubber is used than in hard switching. The turn-off losses increase strongly with temperature and also with the transistor current at turn-off. There is a significant increase in turn-off losses with increasing gate resistance.<>