Wireless power supply device, wireless power receiving device, wireless power transmission system, and wireless power supply method

A wireless power receiving device that alternately performs a wireless communication operation and a wireless power receiving operation, comprising:

• a receiving coil configured to receive an AC (alternating current) magnetic field to thereby obtain an AC voltage;
• a rectifier circuit configured to rectify the AC voltage, thereby to obtain a DC voltage;
• a communication stabilizing circuit configured to stabilize the DC voltage, thereby to obtain a communication operation voltage for the wireless communion operation;
• a power supply stabilizing circuit configured to stabilize the DC voltage, thereby to receive power in the wireless power receiving operation;
• and
• a communication control circuit configured to receive the communication operation voltage, to perform the wireless communication operation, and to control the power supply stabilizing circuit.

A wireless power receiving device configured to receive a receiving power from a wireless power supply device, comprising:

• a resonant circuit including
• a receiving coil configured to receive an AC magnetic field from the wireless power supply device to thereby obtain an AC voltage, and
• a resonant capacitor;
• a capacity change circuit configured to change a capacity of the resonant capacitor;
• a supply line configured to receive a supplied voltage rectified from the AC voltage;
• and
• a current voltage measuring circuit configured to measure a current flowing through the supply line and the supplied voltage, thereby to calculate a receiving power, the capacity change circuit changing the capacity of the resonant capacitor based on whether the calculated receiving power exceeds a prescribed threshold range.