Wireless Charging: All Set for Takeoff

Mobile device solutions
Convenience is one of the key drivers for consumer mobile solutions being the first adopters of wireless power technology. Devices such as cellphones, tablets, media players, and mobile TVs require different adaptors with different interface connectors, meaning one needs to carry many connectors and adaptors to serve the same purpose of transferring charge into a device. A universal wireless adaptor with a powerful supporting infrastructure and ECO system can address this inconvenience. Having the solution available in cars, coffee shops, restaurants, trains, airplanes, offices etc. will support the need for this convenience.

Another important factor is technology upgrades in mobile solutions that generate a greater demand for power from the device’s battery, meaning the convenience of wireless charging is of even greater interest.

Referring to Figure 1, we can see that for maximum flexibility, we need a sophisticated system to control the transmission and reception of the power.

Magnetics
There are many similarities between the architectures of MI and MR technologies. For example, both use a magnetic field as a bridge to transfer power.

In both technologies, current through a resonant circuit creates a magnetic field to transfer power. The alignment of the receive and transmit coils in the flux field and the distance between them determines how efficiently energy is transferred; greater separation between transmit and receive coils results in less efficient power transfer. Resonant frequency, the ratio of transmit to receive coil dimensions, coupling factor, coil impedance, skin effect, AC and DC elements, and the parasitics of the coil are other factors that have a large impact on how efficiently energy is transferred.

It is given that as the X, Y, and Z separation and the proportional angle between transmit and receive coils increases, the losses and efficiency will be greatly impacted.

Depending on the requirement, including cost and size considerations, a single or multiple coil solution can be employed in both MI and MR technologies. Figure 2 provides an overview of typical coil structures.

Power management
Development of high-performance power management architectures has a big impact on the implementation of successful MI and MR solutions. On the transmitter side, in order to induce current into the resonant circuit, a DC-to-AC conversion takes place. In MI technology, a half-bridge or full-bridge inverter is used for this conversion whereas in MR technology current is supplied from a power amplifier.

Conclusion
It is reasonable to conclude that the best potential solution for a specific application will be based on the required features and performance. If free positioning or multi-device charging capability in X, Y, and Z directions is required, magnetic resonance is probably the preferred solution. If high efficiency performance with strong standards-compliance is required, then WPC-compliant solutions may represent the optimum choice. However, there is no question that a multimode solution able to seamlessly recognize the coupled MI- or MR-based device and transfer power effectively and efficiently will be the ideal solution to serve such applications.