Patent ID: 8884468

Claim:
Circuitry for use in a primary unit of an inductive power transfer system to generate an electromagnetic field so as to transfer power wirelessly by electromagnetic induction to one or more secondary units of the system, the or each secondary unit being separable from the primary unit, the circuitry comprising: a plurality of drivable portions, at least one of said plurality of drivable portions comprising a primary coil and at least one of said plurality of drivable portions comprising a dummy coil; driving circuit operable to supply both or at least two of said portions with drive signals so as to cause those driven portions that have a said primary coil to generate said electromagnetic field; and control circuit operable, in dependence upon a feedback signal indicative of a characteristic of the primary coil or dummy coil of one or more of the driven portions, to control the circuitry so as to tend to regulate said feedback signal, wherein the circuitry is configured so that: those portions that are driven are connected together in parallel and have a tuned resonant response; and said control tends to regulate a characteristic of each of said driven coils.