Low Inductance Switching for SiC MOSFET Based Power Circuit

Wide Band Gap power semiconductor switching devices offer superior performance compared to an equivalent Si power device. SiC MOSFETs can be competitive when compared to Si IGBTs of the same voltage class, whilst offering greater benefits at high switching frequencies. Operating SiC MOSFETs at high switching frequencies imposes significant challenges, including: Ringing and voltage overshoot issues, making accurate high bandwidth measurements, and the requirement for a high-performance gate drive circuit. This paper presents a prototype low inductance PCB design for a SiC MOSFET switching circuit. In addition, a linear current gate-drive circuit and a high bandwidth on-board measurement system have been developed and the designs for these are presented. The measurement system showed good agreement with the external probe measurements and superior bandwidth. Hard-switching tests with a 900V SiC MOSFET showed that the dV(DS)/dt becomes largely invariant to changes in load current when using a current source gate drive. The measured dV(DS)/dt slew rates are compared with the dV(DS)/dt slew rates estimated from the parameter values given in the SiC MOSFET datasheet, and the two sets of results show good agreement. In this paper, the performance of an optimised circuit is successfully demonstrated and the benefits are discussed.