Switching characteristics of MCT's and IGBT's in power converters

The performances of the Insulated Gate Bipolar Transistor (IGBT) and MOS-Controlled Thyristor (MCT) in hard- and soft-switching applications are studied in detail, both experimentally and by using numerical simulations. Simulated results show good qualitative agreement with the measured data under a wide range of circuit operating conditions. The simulation results are obtained from an advanced mixed device and circuit simulator in which the device under test (DUT) is represented by a two-dimensional (2-D) grid structure and the internal plasma dynamics is studied using finite element numerical solution technique. A comparison is then made between the switching performance of the bipolar transistor-like device (IGBT) and a thyristor-like device (MCT) in power converters. It is shown that due to a basic difference in the turn-off mechanism, whereas an IGBT shows a tail-current `bump' due to electric field buildup during turn-off, the MCT shows a turn-off `shoulder' due to current flow through the turn-off MOS channel. This leads to much higher losses for MCT than IGBT under identical operating conditions. Furthermore, since the turn-off of MCT involves removal of more carriers from the drift-region, the turn-off is slower than IGBT.