Capacitor-clamped Cascode Normally-on SiC JFET operates as Synchronous Rectifier

摘要

Normally-on Silicon Carbide (SiC) Junction Field Effect Transistors (JFETs) have been used in cascoderncircuits for some time. The traditional circuit has the disadvantage that the switching speed canrnbe hard to control, resulting in high losses or poor EMI. This paper introduces the capacitor clampedrncascode, which offers new degrees of freedom in controlling switching speeds and still retains the advantagesrnof a simple gate drive. The capacitor clamped cascode when used with SemiSouth’s normally-rnon “trench” SiC JFET can also be used as a synchronous rectifier, eliminating extra catch diodesrnneeded during switching transitions and possible fault conditions. This synchronous rectification hasrnsignificant advantages in inverter and bridge configurations where the freewheeling diode can bernsaved, not only reducing system cost but also improving efficiency. This paper analyses the switchingrnin the cascode, starting with the basic switching principles and component voltages with experimentalrnresults comparing test results with and without the catch diode.