A relation between dynamic saturation characteristics and tail current of nonpunchthrough IGBT

This paper describes a relation between dynamic saturation characteristics and turn-off loss of nonpunchthrough (NPT) IGBT for the first time. By experiment and numerical simulation, it was found that the turn-off loss, ESW(off), of NPT-IGBT strongly depends on the on-state pulse width, tw(on), ESW(off) increases with increasing tw(on), and this characteristics strongly depends on the thickness of the n-drift layer and the forward voltage drop. This is because the NPT-IGBT´s dynamic carrier saturation speed determined by the hole velocity is much slower than that of PT-IGBT. Further, it is reported for the first time that the true ESW(off) of NPT-IGBT is two or three times larger than the turn-off loss value calculated using the ordinary definition (i.e. 90% of V_CE to 10% of I_C). This is due to the power loss contribution generated by the tail current under 10% of I_C which continues for more than several tens of microseconds. From these facts, the temperature rise in the NPT-IGBT during switching is higher than the value to be expected from the turn-off time specified in the data sheets. These results should be noticed in the thermal design of power applications using NPT-IGBT