Patent 7279850 was granted and assigned to Auckland Uniservices Limited on October, 2007 by the United States Patent and Trademark Office.
Power taken inductively from the alternating current in a track is received by a resonant circuit which is output controlled by a switching circuit asynchronous with the frequency of the power supply. The switch on and off time is controlled to regulate the output power and the circuit is such that on light loads the resonant circuit decouples from the track.