A power converter including a controller to control a synchronous rectifier (SR) switch. The controller includes a request control circuit and a discharge prevention circuit. The request control circuit is configured to generate a request signal in response to an output of the power converter. The request control circuit generates a secondary control signal to control the SR switch. The discharge prevention circuit is configured to prevent a parasitic capacitance discharge of a power switch caused by a turn on of the SR switch. The discharge prevention circuit is further generates a prevent signal to disable the secondary control signal from control of the synchronous rectifier switch when a period of the request signal is greater than a first time threshold, and enable the secondary control signal to control the synchronous rectifier switch when the period of the request signal is less than a second time threshold.