An exemplary power supply circuit (200) includes a pulse width modulation circuit (220) providing a pulse signal, a voltage conversion circuit (210) converting a primary voltage to an output voltage according to the pulse signal, a feedback circuit (260), and a control circuit (290). The feedback circuit includes a sampling branch (261) detecting a current of the voltage conversion circuit and accordingly providing a feedback signal, and a voltage division branch (262) electrically coupled to the sampling branch. The control circuit is electrically coupled to the voltage division branch, and is configured for disabling the voltage division branch after a predetermined period of time when the output voltage is within a predetermined range.