Wireless power feeder and wireless power transmission system

A wireless power feeder for feeding power by wireless from a feeding coil to a receiving coil at the resonance frequency of the feeding coil and receiving coil, comprising:

• a power transmission control circuit that feeds AC power to the feeding coil at the drive frequency;
• a feeing coil circuit that includes the feeding coil and a capacitor and resonates at the resonance frequency;
• a phase detection circuit that detects the phase difference between the voltage phase and current phase of the AC power and generates a phase difference indicating voltage in accordance with the magnitude of the phase difference;
• and
• a reset circuit that is connected to a voltage line to which the phase difference indicating voltage is fed so as to reduce the phase difference indicating voltage, wherein
• the power transmission control circuit includes first and second current paths and makes first and second switches connected in series respectively to the first and second current paths alternately conductive to feed the AC power to the feeding coil,
• the phase difference indicating voltage output from the phase detection circuit is input to the power transmission control circuit,
• the power transmission control circuit adjusts the drive frequency so as to reduce the phase difference according to the phase difference indicating voltage to allow the drive frequency to track the resonance frequency, and
• the reset circuit reduces the phase difference indicating voltage when the phase difference indicating voltage exceeds a predetermined threshold.