Patent ID: 7683598

Claim:
A power supply circuit comprising: an input pin receiving a voltage of either a first predetermined value or a second predetermined value smaller than the first predetermined value; a first output pin for which an output of a voltage of either the first or second predetermined value is required; a second output pin for which an output of a voltage of the second predetermined value is required; a DC-DC converter generating an output voltage from the voltage of the input pin in either a step-down mode or a boost mode and outputting the output voltage to at least one of the first and second output pins in accordance with a combination of the voltage value of the input pin and the voltage value required for the first output pin; a first bypass switch circuit turning on to output the voltage of the input pin to the first output pin when the voltage is not output to the first output pin from the DC-DC converter; a second bypass switch circuit turning on to output the voltage of the input pin to the second output pin when the voltage is not output to the second output pin from the DC-DC converter; a start control circuit causing the DC-DC converter to operate in the step-down mode irrespective of the combination of the voltage value of the input pin and the voltage value required for the first output pin during the period from when the DC-DC converter is started until the output voltage of the DC-DC converter becomes equal to the voltage of the input pin; and an output slope control circuit synchronizing a rising slope of the output voltage of the first bypass switch circuit with a rising slope of the output voltage of the DC-DC converter when the first bypass switch circuit turns on and synchronizes a rising slope of the output voltage of the second bypass switch circuit with a rising slope of the output voltage of the DC-DC converter when the second bypass switch circuit turns on.