The Cascode Junction Field Effect Transistor  is a combination structure that uses a low-voltage MOSFET as an auxiliary switch to convert a high-voltage normally-on JFET into a normally-off device. In this article, we combine the advantages of GaN's fast switching speed, simple gate drive circuit, and the high breakdown voltage of SiC. Firstly, a 650V normally-off cascode device is built using a low-voltage GaN and a high-voltage normally-on SiC JFET. The Miller platform is no longer available during the gate turn-on and turn-off process of the SiC JFET, and the SiC JFET can work at higher frequencies. The working principle and switching process of the Cascode device are analyzed in detail, and then the double pulse test and the half-bridge LLC resonance are built. The converter experiment platform compares the switching loss and switching speed of GaN/SiC Cascode, Si/SiC Cascode and Si MOSFET at different current levels, and conducts efficiency tests in actual application circuits. The results show that compared with other devices, GaN/SiC Cascode devices have faster switching speeds, smaller switching losses and higher efficiency, and have good application prospects.
 

GaN/SiC Cascode; working principle; switching loss; double-pulse test; LLC resonant converter