Method and apparatus for supplying energy to a medical device

A method for controlling transmission of wireless energy supplied to an electrically operable medical device when implanted in a patient, wherein the method comprises transmitting said wireless energy from an external energy source located outside the patient, and receiving said wireless energy by an internal energy receiver located inside the patient, the internal energy receiver being connected to the medical device for directly or indirectly supplying received energy thereto, the method further comprising:

• determining an energy balance between the energy received by the internal energy receiver and the total energy used for the medical device,
• determining the energy balance, by an internal control unit or external control unit, during the transmission of wireless energy,
• transmitting feedback information from inside the body to be able to control the wireless energy supply sent by the external energy source,
• and
• controlling the transmission of wireless energy from the external energy source, based on the determined energy balance, the transmission of wireless being controlled in accordance with at least one of:
• an energy reception rate in the internal energy receiver compared to an total rate of used energy being consumption rate, storage rate or combined consumption and storage rate, and
• directly or indirectly measuring over time the difference between the total amount of energy received by the internal energy receiver and the total amount of used energy being consumed, stored or combined consumed and stored energy, and determining the energy balance based on at least one of:
• said difference and a detected change in said difference.