Transmitter Coil Power Foreign Object Detection

Systems, methods and apparatus for wireless charging are disclosed. A wireless charging device has a resonant circuit including one or more power transmitting coils in a charging surface of the charging device, a driver circuit configured to provide a charging current to the resonant circuit, and a controller. The controller is configured to determine an average transmitted power using samples of current and voltage captured from the resonant circuit, and determine that a foreign object is located on or near the charging surface when the average transmitted power exceeds a measurement of received power provided by a receiving device and parasitic losses associated with the wireless charging device. In one example, each sample of current is obtained by measuring a current flowing in the resonant circuit, and each of sample of voltage is obtained by measuring a voltage across the one or more power transmitting coils.