A 200 °C Safety System at Power-Up of Normally On SiC JFETs Inverters

Silicon carbide (SiC) power devices are the only commercialized components to run at high voltage and high temperature. Normally on junction field-effect transistors (JFETs) have lower on-state resistance and lower output capacitance than other SiC switches, which reduces conduction and switching losses. However, normally on power devices induce a short-circuit in voltage-fed inverters (VFI) when the gate driver is not powered prior to the bus supply. This is a power-up limitation that has not received much attention in the literature, especially for safety systems that can be used in an integrated circuit capable of running at elevated temperature. This paper describes an original solution based on SiC JFETs to secure the inverter operation at power-up without gate driver supply for the SiC JFETs. The reliability test of the protection circuit and his impact on the ageing of the JFET of the VFI are also presented. The safety system is capable of running in elevated ambient temperatures. Experimental results have been carried out in a 540 V, 10 A inverter and at ambient temperatures from 27 to 200 °C.