CONTACTLESS POWER RECEIVER AND METHOD FOR OPERATING SAME

1 . A contactless power system comprising a power transmitter having a transmitting coil and a power receiver having a receiving coil, the power receiver being configured to receive power transmitted by the power transmitter via contactless electromagnetic coupling of the respective coils and deliver the received power to a load, wherein the receiving coil of the power receiver is part of a resonant circuit having a resonant frequency, the resonant circuit comprising a detuning element to detune the frequency of the resonant circuit from the resonant frequency in accordance with power requirements of the load.

2 . A system as claimed in claim 1 , wherein the receiving coil is an inductance element and the resonant circuit of the power receiver comprises the inductance element in series with a capacitive element, the inductance and capacitance values of the inductance and capacitive elements being selected to provide the resonant frequency.

3 . A system as claimed in claim 2 , wherein the detuning element of the resonant circuit is configured as part of the capacitive element.

4 . A system as claimed in claim 3 , wherein the detuning element is a variable capacitor.

5 . A system as claimed in claim 4 , wherein the variable capacitor comprises a capacitor in series with a switch.

6 . A system as claimed in claim 5 , wherein the power receiver comprises controller configured to receive one or more signals in accordance with the power requirements of the load and to control operation of the switch in accordance with the received signals thereby varying the capacitance value of the variable capacitance and detuning the frequency of the resonant circuit from the resonant frequency.