A method and apparatus for predicting the discharge time of magnetic device are provided. A switching circuit generates a switching signal and an auxiliary signal. The switching signal is used to regulate the switching regulator. The auxiliary signal is used to control the synchronous rectifier. An evaluation circuit generates a timing signal in response to an input signal and the switching signal. The input signal is correlated to the input voltage of the switching regulator. The timing signal is formed for turning off the synchronous rectifier for preventing a reverse current under light load and no load conditions.