The SG6203 is designed to control and drive the synchronous rectifier for the flyback converter. The synchronous signal of the primary switch is obtained by a single diode connected between the transformer secondary winding and the SG6203. Using the SG6203, no additional transformer winding is required and the circuit complexity can be minimized. The power unit can be properly operated under discontinuous conduction mode (DCM) or continuous conduction mode (CCM). Problems such as "shoot-through" or "cross conduction" in CCM and energy-reverse from the secondary to the primary in DCM are prevented by the SG6203 design.