A power supply for power factor correction and a driving method thereof wherein a ripple current of a power factor correction circuit (PFC) can be reduced to enhance a power factor and an efficiency. In the power supply, a power factor correction circuit corrects a power factor of a AC voltage supplied from an AC voltage source using a switching device to convert it to a DC voltage. A DC to DC converter converts said DC voltage from the power factor correction circuit into a desired DC voltage. A controller controls the switching device in accordance with an input voltage inputted to the power factor correction circuit to vary an output voltage of the power factor correction circuit.