FOREIGN OBJECT DETECTING DEVICE, WIRELESS POWER TRANSMITTING APPARATUS, AND WIRELESS POWER TRANSFER SYSTEM

摘要

A foreign object detecting device includes first, second, and third coils (11a,11b,11c) and a foreign object detecting circuit (10). The foreign object detecting circuit outputs a first detecting signal (S1) having a first predetermined waveform to a first terminal (T1) of the first coil (11a) and outputs a second detecting signal (S2) having a second predetermined waveform, which is an inverted form of the first predetermined waveform, to a fifth terminal (T5) of the third coil to cause a combined magnetic field extending over the first and third coils. The foreign object detecting circuit (10) measures an amount of change of the impedance value of the first or third coil with respect to a change in the combined magnetic field in the case of the presence of a foreign object (20). The amount of change exceeds a predetermined value, the foreign object detecting circuit determines that there is a foreign object above the second coil.