MOS controlled thyristor turn-off modeling results

The MOS Controlled Thyristor (MCT) is presently under development. It has been observed that the MCT´s maximum controllable current depends on its gate voltage rise time. Research, using a detailed computer model of a single MCT cell, has been conducted to understand the origin of this phenomenon. It is found that the MCT cell´s turn off transient is substantially different when it is turned off driven from a voltage source as compared to when it is driven from a current source. An MCT cell turning off driven from a voltage source models the situation of a single MCT cell turning off in parallel with many other MCT cells since a change in one cell´s current cannot change the voltage across itself. This voltage is determined by the combined effect of the many other cells. The voltage source turn off results explains the MCT´s maximum controllable current dependence on gate voltage rise time. These results also lead to the proposal that the interaction of many parallel MCT cells can be modeled using just two cells in parallel. The two cells should have very unequal current ratings. The higher current rated cell creates the voltage source for the lower current rated cell being studied