Patent ID: 8085560

Claim:
A power supply apparatus, comprising: a transformer to convert input power supplied to a primary winding so as to induce an output current and an output voltage in a secondary winding; a current detector to detect the output current of the secondary winding of the transformer; a voltage detector to detect the output voltage of the secondary winding of the transformer; a switch to adjust the output voltage outputted by the transformer; and a controller to control the switch to maintain an output power of the transformer obtained by multiplying the output current by the output voltage to be within a predetermined level, wherein the current detector comprises a current transformer connected to the secondary winding of the transformer to induce the output current according to a turns ratio, a photocoupler light emitter to emit light by a current of the secondary winding of the current transformer, and a photocoupler light receiver coupled to a feedback terminal of the controller to receive the light from the photocoupler light emitter.