Thermal Impedance Identification of a SiC JFET Module

Abstract:
This paper proposes a method to estimate the junction temperature of a SiC JFET by evaluation of the voltage drop of the internal gate source diode. This information is used to identify the thermal impedance. First, the voltage drop of the diode is characterised with the SiC JFET heated by a heating plate. Secondly, the thermal path from junction to fluid is modelled and analysed. The device is heated by on-state power dissipation, and the cooling down process is evaluated to calculate the thermal impedance. In this context, the influence of fluid temperature, power loss and flow rate is appraised. Finally, a gate drive circuit with associated simulations is presented which is capable of measuring the temperature-dependent forward and breakdown voltage of the gate source diode during switching operation.