Patent ID: 8829725

Claim:
A wireless power feeder that wirelessly feeds power from a power feeding coil to a power receiving coil using a magnetic field resonance phenomenon between the power feeding coil and the power receiving coil, the feeder comprising: the power feeding coil; a power transmission control circuit that feeds AC power to the power feeding coil at a drive frequency so as to make the power feeding coil feed the AC power to the power receiving coil; a phase detection circuit that detects a phase difference between voltage and current phases of the AC power; a signal receiving coil that receives, from the AC power receiving side, an output signal having a duty ratio indicating an output level; and a signal adjustment circuit that DC-converts the output signal in accordance with the duty ratio, the power transmission control circuit adjusting the drive frequency so as to reduce the phase difference, the phase detection circuit performing ex-post adjustment of the detected value of one or both of the voltage and current phases in accordance with a signal level of the DC-converted output signal.