The AP436 is a high-speed controller designed to drive N-channel power MOSFET used as synchronous rectifiers in high current, high frequency fly-back converters. The circuit does not require any ties to the primary side and derives its operating power directly from the secondary. The circuit functions are structured by anticipating transformer output transitions then turns the power MOSFET on or off before the transitions of the transformer to minimize body drain diode conduction and reduce associated losses.