Wireless charging solutions have two key elements; the transmitter and the receiver. The transmitter contains a MOSFET-based inverter to convert the DC power into an AC waveform to drive the coil and create the alternating magnetic field. In order to provide the flexibility and functionality required, the inverter is controlled by a wireless power controller in real time through the associated MOSFET driver components. The receiver contains a rectifier to convert the incoming AC waveform into DC power and a regulation stage to provide a conditioned supply to the load. Most receivers also contain a wireless power controller which is responsible for overall system management and communication.
Two types of technology are commonly used to transfer power wirelessly through alternating magnetic fields - inductive and resonant. Reflecting the different benefits of these two technologies, there are two standards bodies active in the wireless charging market: the Wireless Power Consortium (WPC) and the AirFuel Alliance. The main differences between the two standards are shown in figure 2 at a glance.
The Wireless Power Consortium (WPC) supports the Qi standard for wireless charging, which is the leading standard in the market. Qi uses inductive technology that supports efficient and tightly coupled charging. In addition, the upcoming version of the WPC Qi standard contains provisions that create a certified authentication standard. OPTIGA Trust Qi is Infineon's turnkey IoT security solution, designed to meet the challenges of secured wireless charging required by the Qi standard.
The single coil inductive approach is the most prevalent solution on the market and consists of a single transmitter coil operating between 80 - 205kHz. This approach requires centering the device to be charged in relation to the transmitter coil and is only able to charge a single receiver device at a time. With good design and high-quality power conversion electronics the efficiency of this type of charging can match wired charging. Extending this approach to a charger with a multi-coil array brings an additional benefit. The positioning of the device is much less precise and smart systems can detect which coil is closest to the device being charged and direct the power accordingly.