Patent ID: 8416593

Claim:
A switching power supply, comprising: a rectifier circuit for rectifying an input voltage into a first direct current voltage; a converter for generating a first current according to the first direct current voltage; a detecting unit for generating a detected voltage according to the first current; a control unit for generating a control signal; a switching unit for enabling the converter, and conducting the first current to the detecting unit when receiving the control signal; and a protection unit for comparing the detected voltage with a zener voltage and conducting the first current to ground when the detected voltage is equal to or higher than the zener voltage; wherein the switching unit is not disabled when the protection unit shunts the first current, the control unit stops generating the control signal when determining that the detected voltage is equal to or higher than a predetermined value; wherein the protection unit is further configured for shunting the first current with the detecting unit and the switching unit when the first current becomes so large to breakdown the switching unit, the protection unit operates when the control unit is short circuited to ground.