WIRELESS POWER TRANSFER

A power transmitter (101) provides power to a power receiver (105) via an inductive power transfer signal. An output circuit (203, 103) generates the power transfer signal in response to a drive signal generated by a driver (201). A communicator (207) transmits messages to the power receiver (105) using amplitude modulation and receives messages from the power receiver (105) using load modulation. A controller (205) controls the driver (201) to generate the power transfer signal to apply a repeating time frame comprising a power transfer interval during which the power transfer signal is arranged to transfer power to the power receiver (105) and a communication time interval during which no power transfer signal is generated. A synchronizer (209) controls the power transmitter to transmit at least part of a first message from the power transmitter (101) to the power receiver (105) during a power transfer time interval and to receive a response message from the power receiver (105) during a communication time interval.