The influence of turn-off dead time on the reverse-recovery behaviour of synchronous rectifiers in automotive DC/DC-converters

The current commutation from the channel into the body diode of a MOSFET synchronous rectifier as well as the relation of the PWM turn-off dead time and its reverse-recovery behaviour were simulated and investigated experimentally. Both, reverse-recovery charge and current can be reduced significantly by shortening the dead time to few 10 ns. It leads to an overall converter loss reduction of several percent. The improvement of the reverse-recovery behaviour is based on the turn-on dynamics of the diode. In the considered case it takes several 10 ns to enhance plasma in the n^--region of the body diode. Therefore, turning off of the synchronous rectifier before the plasma has reached a steady-state will lead to a lower reverse-recovery charge.