Power supply circuit

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