Abstract: A circuit controls a control signal of a free-wheeling switch and has a switch in series with the control signal signal. A timer has an output that controls the switch. The timer opens the switch for a predetermined time and closes the switch afterwards. In other embodiments, a free-wheeling switch circuit is provided for a synchronous switching power supply having an input and a pre-biased output. The switch circuit has an inductor, a first switch connected to the inductor and having a first control input, a first control signal source, a second switch having a second control input and being connected between the first control signal source and the first control input, and a control circuit having an output in communication with the second control input. The control circuit opens the second switch for a predetermined time and then closes the second switch.

Abstract: A drive circuit for a synchronous rectifier has a transformer having a main secondary winding and an auxiliary secondary winding. A first switch and a second switch each have a pair of terminals, a terminal of the first switch being connected to the first end of the main winding, a terminal of the second switch being connected to the second end of the main winding, and each remaining terminal of the first and second switch being connected together. A third switch connects between the second end of the main winding and the first end of the auxiliary winding, wherein the third switch periodically closes to connect the main winding and the auxiliary winding in series, a drive voltage being developed by the connected main and auxiliary windings being used to control at least one of the first switch and second switch.