Patent ID: 7092261

Claim:
A switching power supply, comprising a rectifier which receives an input voltage and converts the input voltage into a rectified DC voltage; a switch device connected to the rectifier; a transformer connected to the switch device for transducing the rectified DC voltage into a magnetization energy by a primary winding and transferring the magnetization energy across a secondary winding according to on/off operations of the switch device; a switching control circuit which generates a switching control signal to regulate a duty cycle of the switch device; and an oscillator frequency tuner that modulates an oscillator frequency of the switching control circuit according to a feedback control signal provided by the switching control circuit to broaden a maximum duty cycle of the switching control circuit wherein the oscillator frequency tuner includes a plurality of capacitors connected between a reference voltage output of the switching control circuit and a ground terminal, and at least one bypass switch coupled across at least one of the plurality of capacitor for controlling the charging and discharging operation of the capacitor coupled therewith when the switching power supply is operating under a peak load condition.