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