SWITCHING CIRCUITS

摘要

We describe a protection circuit for a normally-on silicon carbide JFET, comprising a first power switching connection coupled to the JFET drain; a gate driver circuit; and a normally-off MOSFET in series between the JFET source and a second power switching connection. The circuit includes a diode having an anode coupled to JFET gate and a cathode coupled between a second power switching connection and a source/drain connection of the MOSFET. A control circuit is coupled to the gate of the MOSFET to sense a failure of a power supply to the gate driver circuit and to switch off the MOSFET in response, for example using a bias circuit powered from this power supply. When the MOSFET is off the external power maintains the gate of the JFET negative with respect to the source, via a circuit including the internal capacitance of the off MOSFET and the diode.