BACKGROUND

Wireless power transfer is the transmission of electrical energy from a power source to an electrical load without the use of man-made conductors to connect the power source to the electrical load. A wireless power transfer system includes a transmitter and one or more receiver devices. The transmitter is electrically coupled to a source of power and converts the power to a time-varying electromagnetic (EM) field. The one or more receiver devices receive the power via the EM field and convert the received power back to an electric current to be utilized by an electrical load that is either part of the receiver device or is electrically coupled to the receiver device.

The receiver devices are configured to resonate at the characteristic frequency at which the transmitter is operating in order to receive power from the near EM field. The receiver devices convert the received power from the near EM field into an electrical current that can then be used to power an electrical load that is part of, or that is electrically coupled to, the receiver device.

One of the difficulties associated with current receiver devices used in wireless power transfer systems is ensuring that a constant voltage or current, depending on which is needed, is provided to the electrical load. Another difficulty associated with current receiver devices used in wireless power transfer systems is the lack of a mechanism for shutting down the resonant response of the receiver device when electrical power is not needed by the load. If the resonant response is not shut down when power is not needed, the receiver device will waste power and dissipate heat whenever the load is not using a large fraction of the available power. In known receiver devices that provide a mechanism for shutting down the resonant response, the mechanism typically includes a high-speed switching circuit implemented using expensive high-speed components.

A need exists for a receiver device for use in wireless power transfer systems that is capable of providing a constant current or voltage, depending on which is needed, to the load. A need exists for a receiver device for use in wireless power transfer systems that is capable of shutting down the resonant response when electrical power is not needed by the load to reduce power consumption and avoid unnecessary heat dissipation.

