Patent ID: 8395352

Claim:
A power transmission control device provided in a power transmission device included in a contactless power transmission system in which power is transmitted from the power transmission device to a power receiving device by electromagnetically coupling an elementary coil and a secondary coil and the power is supplied to a load of the power receiving device, the power transmission control device comprising a load state detection circuit that detects a load state of the power receiving device on the basis of a differential signal between a first signal from a first end of a resonance capacitor forming a resonant circuit with the elementary coil and a second signal from a second end of the resonance capacitor, wherein the load state detection circuit includes: a differential amplifier that outputs an amplifier output signal corresponding to the differential signal; and a phase difference detection circuit that detects a phase difference between the amplifier output signal from the differential amplifier and a reference clock signal and outputs a phase difference signal.