Patent 7474062 was granted and assigned to Auckland Uniservices Limited on January, 2009 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 at least partially decoupled by a switching circuit asynchronously with the frequency of the power supply. The switch on and off time is controlled to regulate the output power, either the voltage or the current output being a function of the switch off time divided by the switch on time.