An apparatus includes a controller configured to control switches of a receiver, the receiver comprising a first receiver coil configured to be magnetically coupled to a transmitter coil of a wireless power transfer system, a rectifier circuit coupled to two terminals of the first receiver coil, a second receiver coil and a first auxiliary switch, wherein the second receiver coil is connected in series with the first auxiliary switch, and the second receiver coil is configured to be magnetically coupled to the transmitter coil, and wherein in response to a low power mode of the apparatus, the controller is configured to turn on the first auxiliary switch such that the first receiver coil and the second receiver coil are connected in series to boost a gain of the wireless power transfer system.