Patent ID: 7586364

Claim:
A power supply voltage controlling circuit that controls an output voltage at an output terminal to a desired set voltage, comprising: a voltage regulator circuit that is connected to a first power supply and a second power supply that outputs a higher voltage than said first power supply, supplies a current to said output terminal from at least any of said first power supply and said second power supply, and compares the output voltage at said output terminal with a first reference voltage to adjust said output voltage to approach said first reference voltage; and a controller circuit that supplies said first reference voltage to said voltage regulator circuit and controls said voltage regulator circuit by outputting, to said voltage regulator circuit, at least any of a first enable signal for enabling said first power supply to supply a current to said output terminal and a second enable signal for enabling said second power supply to supply a current to said output terminal, wherein said controller circuit has a regulator selecting circuit that compares the voltage of said first power supply with a second reference voltage and outputs said second enable signal if the voltage of said first power supply is lower than said second reference voltage.