Abstract: A DC-DC power converter includes an input, an output, a transformer, a primary field-effect transistor (FET), and a synchronous rectifier. The synchronous rectifier includes a drain that experiences multiple resonant voltage valleys during each dead-time period of the converter. The converter further includes a synchronous rectifier drive circuit configured to turn on and turn off the synchronous rectifier, and a primary control circuit. The primary control circuit is configured to operate the primary FET in a valley skipping mode, and to transmit a drive signal to the synchronous rectifier drive circuit to turn on the synchronous rectifier during a specified one of the multiple resonant voltage valleys to generate a negative current through the synchronous rectifier. Methods of operating a DC-DC power converter are also disclosed.

Abstract: A DC-DC power converter includes an input, an output, a transformer, and a primary FET coupled to selectively conduct current though a primary winding of the transformer. The primary FET includes a drain that experiences multiple resonant voltage valleys during each dead-time period of the converter. The converter further includes a synchronous rectifier coupled to selectively conduct current through a secondary winding of the transformer, and a control circuit. The control circuit is configured to operate the primary FET in a valley skipping mode by turning on the primary FET during a second or subsequent one of the multiple resonant voltage valleys, and to allow a negative current in the secondary winding of the transformer before turning off the synchronous rectifier during one or more of the multiple resonant voltage valleys. Methods of operating DC-DC power converters are also disclosed.