Patent ID: 8760887

Claim:
A power supply circuit having a first power supply and a second power supply, the first power supply being a single power supply providing a first positive-side supply voltage and a first reference potential, the second power supply being a single power supply providing a second positive-side supply voltage and a second reference potential different from the first reference potential of the first power supply, the circuit comprising: a switching element; a switching transformer for generating a voltage in a secondary winding of the switching transformer according to an ON/OFF operation of the switching element connected to a primary winding of the switching transformer; a switching controller operated by the first positive-side supply voltage and the first reference potential, the switching controller controlling an ON/OFF state of the switching element according to a voltage input into a feedback input terminal, said first positive supply voltage being supplied to the switching controller from a primary side of the switching transformer; a reference potential generating section for dividing the first positive-side supply voltage so as to generate the second reference potential; a voltage generating section for generating the second positive-side supply voltage upon receiving the voltage of the secondary winding of the switching transformer; a current mirror circuit for converting the second positive-side supply voltage with respect to the second reference potential into an electric current so as to output the electric current; and a current/voltage converting section for converting the electric current from the current mirror circuit into a voltage with respect to the first reference potential so as to supply this voltage to the feedback input terminal of the switching controller.