Use of the MOSFET channel reverse conduction in an inverter for suppression of the integral diode recovery current

If the integral diodes are used as free-wheeling diodes of a MOSFET half-bridge inverter, the reverse recovery current can be high during the transistor integral diode turn-off. It generates important switching losses and can be induced a transistor failure. This paper shows how to take advantage of the negative channel conduction in a MOSFET to prevent the integral diode conduction and suppress the reverse recovery current. The current is transferred directly from a transistor channel to the opposite one, avoiding the limitation imposed by the diode conduction. This method requires a very fine adjustment of the delay time between the gate drive signals applied to the two transistors to obtain an optimal switching. So the authors propose a method to measure the current during the switching which allows the design of a regulation acting on the transistor gate drive signals, so that they can have switching with a minimal overcurrent transient. The current measurement, when it is integrated into the converter, must be economical, with a large bandwidth. Experimental results showing the reverse recovery current variations and the behaviour of the measurement device integrated into the converter are presented