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 considered is based upon the premise that if the instantaneous current through 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 upon 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 form 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~N might be obtained are discussed