Patent ID: 7633774

Claim:
A power supply apparatus for outputting a predetermined voltage based on an alternative voltage on which a communication signal is superimposed, the alternative voltage being supplied from a power line and having a first frequency, and the communication signal having a second frequency higher than the first frequency, the power supply apparatus comprising: a transformer which has a primary winding and a secondary winding, the primary winding transmitting the communication signal to the secondary winding, the communication signal being superimposed on the alternative voltage; and a capacitor which has impedance characteristics such that impedance at the first frequency is higher than impedance at the second frequency; wherein the primary winding has a first end and a second end, the first end for being connected to the power line through the capacitor, and the second end for being connected to the power line, and wherein the alternative voltage is applied both to the primary winding and the capacitor and the power supply apparatus outputs the predetermined voltage through the capacitor based on the alternative voltage being applied to the capacitor.