Issues in SOA Protection of SiC MOSFETs Using Optocoupler Based Gate Drivers

SiC MOSFETs have gained huge attention in power electronic applications due to their improved characteristics, the potential to increase efficiency and reduce size. The faster switching and reduced chip size of SiC MOSFETs necessitate protection circuits during faults. MOSFETs need to operate inside a safe operating area (SOA) in power electronic circuits. One of the widely used methods, in Si devices for SOA protection, is driving Si devices with optocoupler based gate drivers incorporating desaturation. Although for Si devices SOA protection by optocoupler based drivers are well developed, it has not been investigated thoroughly for SiC devices. This paper investigates the use of optocoupler based gate drivers with desaturation for SOA protection of SiC MOSFETs. A laboratory prototype is developed for testing SiC MOSFETs with optocoupler based gate drivers, sensing diodes and other auxiliary circuits. A detailed study of SOA protection of SiC MOSFETs is performed by analysing the experimental results and parameters of the gate driver circuit. The important issues in SOA protection using the optocoupler based gate drivers are found. The investigations show that faster sensing diodes, proper choice of blanking capacitors and high common mode transient immunity (CMTI) are needed for SOA protection of SiC MOSFETs.