Optimized reverse diode operation of power MOSFETs

The basic structure of a power MOSFET is a pn-junction giving forward blocking capability. In reverse operation the pn-junction is forward biased and the device operates as a conducting diode. Unfortunately this diode has a poor dynamic behaviour. This paper presents an approach to achieve the effect of antiparallel diodes by using the controllable MOS-channel inside the FETs. This new method achieves excellent turn-off behaviour and low on-state losses of the "emulated diode". To get good diode operation mode in a bridge circuit, the interlock time in the control scheme of the two MOSFETs of one bridge leg must be much shorter than in conventional operation. Our working group found that fortunately the optimum interlock time does not depend on the operating conditions of the application circuit. The interlock times of the control scheme may therefore be kept constant. Adaptive adjustment of these times by some kind of status sensing may nevertheless give improved performance.