Contactless power feeding device

A contactless power feeding device for supplying electric power to a power receiving device without contact, the contactless power feeding device comprising:

• a power transmitting circuit configured to transmit alternating-current power;
• and
• a power transmitting resonator which includes a power transmitting resonant circuit including a power transmitting coil and a power transmitting resonant capacitor, wherein
• a resonant frequency of the power transmitting resonant circuit matches a fundamental frequency of the alternating-current power,
• a resonant frequency of the power receiving device matches the fundamental frequency of the alternating-current power,
• input impedance of the power transmitting resonant circuit is set to a first input impedance in a facing state in which (i) a power receiving coil included in the power receiving device is electromagnetically coupled to the power transmitting coil and (ii) a surface of the power receiving coil and a surface of the power transmitting coil are entirely or partially overlapping each other, whereby the power transmitting coil is supplied with the alternating-current power from the power transmitting circuit,
• the input impedance of the power transmitting resonant circuit is set to a second input impedance that is greater than the first input impedance so as to place the power transmitting resonant circuit out of a resonance state, in a non-facing state in which at least one of:
• (i) the power receiving coil is not electromagnetically coupled to the power transmitting coil;
• and (ii) the surface of the power receiving coil and the surface of the power transmitting coil are not overlapping each other, whereby the power transmitting coil is not supplied with the alternating-current power from the power transmitting circuit, and
• an inductance of the power transmitting coil changes in value during a transition from the facing state to the non-facing state, such that the input impedance of the power transmitting resonant circuit increases from the first input impedance to the second input impedance.