A fixed frequency external power source having an external coil is inductively coupled with an implanted coil of an implanted medical device. The implant device has an electronic impedance transformer as part of its load circuit. Such electronic impedance transformer sets a proper voltage and current...http://www.google.de/patents/US6745077?utm_source=gb-gplus-sharePatent US6745077 - Electronic impedance transformer for inductively-coupled load stabilization
