INDUCTIVE POWER TRANSFER SYSTEM

An inductive power transfer system () for coupling a power source to a load across an air gap () is disclosed. The system () comprises a primary unit () associated with a host platform and a secondary unit () arranged to receive power transmitted inductively from the primary unit (). The primary unit () includes a phase detection circuit () configured to detect phase changes in a signal in the primary unit () indicative of changes in an operating condition within the secondary unit (), and a drive circuit (). The drive circuit () is configured to adjust the power level transmitted to the secondary unit () depending on the detected phase.