WIRELESS POWER TRANSFER

A wireless power transmitter () an output circuit () comprises a transmitter coil () for which generates the power transfer signal a drive signal generated by a driver circuit () is applied. A power loop controller () implements a power control loop for controlling the drive signal to adjust a power level of the power transfer signal in response to power control error messages received from the power receiver (). A mode store () stores a plurality of power level modes for the power receiver where each power level mode is associated with a reference power level for the power transfer signal. A mode circuit () adapts the drive signal to set the power level of the power transfer signal to a first reference value in response to receiving a mode request message where the first reference value corresponds to a reference power level for a first power level mode indicated in the mode request message.