A power system includes DC-DC power conversion circuitry that has a first switch and a second switch on either side of a transformer, and the second switch is operates as a synchronous rectifier. Power transfer from a primary side to secondary side of the DC-DC power conversion circuitry is controlled by operating the first switch. A drive signal for the second switch is calculated based on a sensed transformer winding current, and operation of the second switch is controlled based on the drive signal.