Performance limitations of a GTO with near-perfect technology

The performance of multiple-cell devices is limited by a redistribution of current during turn-off, caused by minor differences between the individual cells, which becomes important at high current density. A simple model, based on Gaussian statistics, is proposed where the degree of homogeneity between cells is expressed in terms of a technological quality factor k. It turns out that the increase of turn-off current for a gate turn-off thyristor (GTO) with a large number of cells is highly nonlinear. A major issue is the influence of the external load on the maximum turn-off current of a GTO. In the case of a typical inductive load, the turn-off capability of a device with a small number of segments n (n<100) hardly shows a difference between operation without and operation with a snubber. In contrast, for large GTOs (n>1000) snubberless operation imposes severe limitations on turn-off while a snubber with a realistic leakage inductance allows for a substantially larger turn-off current