An FET-driven power thyristor

Abstract

An experimental power thyristor structure is presented, featuring a bipolar gate as well as an FET-driven gate (n-channel MOSFET) on orthogonal sides of a quadratic chip. Thus, the two turn-on modes can be studied independently of each other on the identical thyristor. In addition, the influence of a switchable cathode-emitter short resistance (p-channel MOSFET), integrated on the same chip, is investigated for both types of gate. A simplified analytical model is proposed, assuming that transport effects, represented by a fictitious time dependence of the transport factors in the n- and p-base on one hand and current dependence of the injection coefficient of the cathode emitter on the other hand, are the only variables dominating during turn-on. A quantitative evaluation of the time-dependent thyristor current yields a theoretical description that is in good agreement with the experiment, both for the bipolar as well as for the FET-driven gate. In either case, measurements with and without the shorted emitter are presented. The FET-drive, inducing anode current without delay, leads to a higher dissipation during turn-on. In addition, the current threshold for turn-on is higher since the FET feeds the n-base rather than the p-base. An FET-driven thyristor thus has the advantage of being voltage controlled while the limit of high di/dt capability is more critical than in the conventional case. An additional feature of the structure presented is its potential to serve as a gate turn-off device.