A controller for controlling a controlled switching device functioning as a synchronous rectifier of alternating current, the controller comprising a control circuit for sensing the direction of current through the controlled switching device, the controlled switching device comprising a MOSFET having a conduction channel and a parasitic body diode and having two main current carrying terminals and a control terminal, the control circuit generating a control signal provided to the control terminal to turn on the controlled switching device approximately when current begins to flow in a first direction through the controlled switching device and turn off the controlled switching device approximately when current begins to flow in a second opposite direction through the controlled switching device, further wherein the control circuit for sensing the direction of current through the controlled switching device main current carrying terminals comprises a sensing circuit coupled across the controlled switching device for comparing a voltage across the controlled switching device to first and second thresholds, the sensing circuit causing the control signal to be generated to turn off the controlled switching device at the first threshold and to turn on the controlled switching device at the second threshold.