MODELS OF DEPENDENCE OF CONTROLLABLE CURRENT ON NUMBER OF ISLANDS IN GATE TURN-OFF THYRISTORS

The maximum controllable on-state current, I(M), of a multi-island GTO , is calculated as a function of the number of islands. The limit cons idered is based upon the premise that if the instantaneous current thr ough the cathode of an island exceeds a critical value i(c), then that island, and hence the GTO, will not turn off. Our approach is based u pon the observed variation in the storage times of individual islands after the initiation of the gate turn-off current. The distribution of storage times is treated as a distribution of random numbers. Both a homogeneous and a Gaussian distribution are treated. The functional fo rm in time of the fall in current through an island, after the storage time was also found to be important. If an island shuts off within a time short compared to the spread in storage times, then I(M) will be small and not scale with the number of islands N. The conditions under which I(M) is similar to N might be obtained are discussed.