Ultrafast Protection of Discrete SiC MOSFETs With PCB Coil-Based Current Sensors

Silicon carbide (SiC) mosfets offer significant advantages in terms of improved efficiency and reduced size of power electronic converters. However, they possess lesser short-circuit withstand time than silicon devices. An ultrafast short-circuit protection scheme for TO-247 packaged SiC mosfets is presented in this article. The protection scheme utilizes printed circuit board (PCB) coils to sense the rate of change of current through SiC mosfets in a half-bridge circuit. The PCB coils are fabricated near a single interconnect trace between the power device and the dc busbar. To ensure minimal intrusion inside the power-loop, the methodology of selecting the minimum trace length for a desired mutual inductance between the coil and the interconnect trace is presented through finite-element analysis. Experimental results for an SiC mosfet subjected to a hard switched fault and a fault under load are presented, and the protection circuit response time under 25 ns is reported. Lastly, the peak current-mode control of a buck converter is implemented using the designed PCB coil-based sensor as current feedback sensor. Therefore, the PCB coil is demonstrated to be an effective alternative for Hall effect and magnetic core-based sensors in current control applications with dc/dc converters.