Energy transfer control adapted to a medical device system

An apparatus adapted to transmit wireless energy from an external energy transmitting device placed externally to a human body to an internal energy receiver placed internally in the human body, the apparatus comprising,

• a first electric circuit to supply electrical pulses to the external transmitting device, said electrical pulses having leading and trailing edges, said transmitting device adapted to supply wireless energy, wherein the electrical circuit being adapted to vary the lengths of first time intervals between successive leading and trailing edges of the electrical pulses and/or the lengths of second time intervals between successive trailing and leading edges of the electrical pulses, and wherein the transmitted wireless energy, generated from the electrical pulses having a varied power, the power depending on the lengths of the first and/or second time intervals, wherein
• the first electric circuit has a time constant, and
• the first electric circuit is adapted to provide the electrical pulses varying the first and second time intervals to have lengths in the range of, in particular lengths that are in the magnitude of order of or are shorter than, the first time constant, and the relationship or proportion between the lengths of the first and second time intervals is varied, whereby, by the varying a varying power is transmitted.