Wirelessly powered devices

A circuit for delivering power to a load from a wireless power supply comprises an inductor coil for placing in the electromagnetic field of an inductor coil of a supply and a switchable capacitor bank with capacitors switchable at least between a series and a parallel configuration. The voltage across the capacitor bank is used as a feedback control parameter for controlling the capacitor bank switching. A voltage regulator is used to supply the load with a constant voltage power supply derived from the capacitor bank output.