Patent ID: 7505290

Claim:
A power supply apparatus comprising: a charge-pump type step-up circuit adapted to charge a step-up capacitor by a power supply voltage, step up a charged voltage of said step-up capacitor using a charge-pump operation, and discharge a stepped-up voltage to a smoothing capacitor via parallel first switch and second switch between the step-up capacitor and the smoothing capacitor, a resistor being connected in series between one of the first and second switches and the smoothing capacitor; and a regulator having a first comparator adapted to compare a voltage corresponding to an output voltage of said step-up circuit with a reference voltage to generate a first comparison output signal and skip a clock signal in accordance with said first comparison output signal, so that the output voltage of said step-up circuit is brought close to a target voltage, discharging of said smoothing capacitor being carried out through the resistor with a predetermined time constant when the output voltage of said step-up circuit is between said target voltage and a voltage lower than said target voltage by a predetermined value.