Techniques for detecting the presence of a foreign object on the surface of a wireless charging transmitter by measuring quality factor during a charging session

Abstract

Inductive charging systems and methods detect a wireless device upon a charging surface of a wireless charging pad including a transmitter coil, determine a first quality factor of the transmitter coil and initiate a charging session, and during the charging session, periodically perform a foreign object detection (FOD) technique including adjusting an operating point of the transmitter coil according to a specific sequence of operating points that causes rectifier diodes between the receiver coil and a receiver load of the wireless device to be reverse biased to disconnect the receiver load from the receiver coil and then determining a second quality factor of the transmitter coil, and detecting whether a foreign object is present on the charging surface based on a comparison between the first and second quality factors.