Difficulties in characterizing transient thermal resistance of SiC MOSFETs

Thermal design is important for safety and reliable operation of power electronics system to cope with emerging loss accompanied by power conversion operation. This paper point outs the difficulties in evaluating transient thermal resistance of power module with SiC MOSFET. The static mode thermal test method to extract structure function of power device utilises K factor of power device to estimate junction temperature. The knee voltage of body diode and threshold gate voltage are utilized as K factor for MOSFET. The estimated junction temperature of SiC MOSFET through the use of K factor gives inappropriate temperature behaviour especially at the onset of thermal test measurement. The anomalous results are observed for different measurement setup type for MOSFET. The dynamic instability of threshold gate voltage occurring in SiC MOSFET violates the estimation of junction temperature with K factor. The larger temperature variation for measurement is effective in mitigating temperature estimation error.