A circuit includes a drain detect circuit. The drain detect circuit receives a sense signal from a secondary side of a power converter circuit, determines, using voltage values of the sense signal, whether a primary side switch of the power converter circuit has been turned on, and assert a switch on detect signal in response to determining that the primary side switch has been turned on. The circuit may assert an enable signal in response to the assertion of the switch on detect signal, and de-asserts the enable signal in response to an assertion of a control signal. The control signal may only allowed to be asserted when the enable signal is asserted. The control signal may control a Synchronous Rectifier device. The power converter circuit may be a flyback converter, and the primary side switch may control a current into a primary-side coil of a transformer.