Investigation of parasitic turn-ON in silicon IGBT and Silicon Carbide MOSFET devices : a technology evaluation

This paper investigates the switching rate and temperature dependence of parasitic (false) turn-on of power transistors when switched in power converters implemented in silicon IGBTs and Silicon Carbide (SiC) MOSFETs. It is shown that although high switching rates are normally desirable for minimizing the switching losses, this can result in shoot-through arm currents due to the combination of a Miller capacitance and high dV/dt. The power losses arising from this can be significantly larger than the normal switching losses since the device will still be blocking a considerable voltage. Even though SiC MOSFETs have a significantly smaller Miller capacitance compared with silicon IGBTs, this problem is no less of an issue due to higher switching speeds and lower threshold voltages. Additionally it is seen that the overshoot current increases with temperatures due to the negative temperature coefficient of the threshold voltage in both device technologies. Various solutions to overcome this have been analyzed for both device technologies. It is seen that the effectiveness of the mitigation techniques differs, and in general due to the lower threshold voltage of the SiC device, the solutions proposed are less effective