An apparatus comprises a rectifier configured to convert an alternating current voltage into a direct current voltage, wherein the alternating current voltage is generated by a receiver coil configured to be magnetically coupled to a transmitter coil of a wireless power transfer system, a high efficiency power converter connected to the rectifier, the high efficiency power converter comprising a first stage and a second stage connected in cascade and a controller configured to detect a plurality of operating parameters and generate a control signal applied to a control loop of the first stage.