The present invention provides a power converter having a phase lock circuit for quasi-resonant soft switching. The power converter includes a first circuit coupled to the feedback signal to generate a switching signal for switching a switching device and regulating the output of the power converter. A second circuit is coupled to an auxiliary winding of the transformer for generating a voltage signal in response to the voltage of the transformer. A phase lock circuit generates a control signal to enable the switching signal in accordance with the voltage signal. The switching signal further turns on the switching device in response to a valley voltage across the switching device.