A synchronous rectifier controller for controlling a rectifier switch is disclosed. The synchronous rectifier controller includes a fully-ON controller and a regulator. Capable of being triggered by a channel voltage of the rectifier switch, the fully-ON controller turns the rectifier switch fully ON for a fully-ON time in view of a predetermined condition. The regulator, disabled during the fully-ON time and enabled after the fully-ON time, turns the rectifier switch ON to regulate the channel voltage within a predetermined voltage range.