Although wireless electricity is without a doubt, an area filled with uncertainty and doubt, the applications for it have proven quite versatile over these past few years. From wireless chargers to inductive-based batteries, there certainly is a need for wireless charging and energy-saving technologies.

Perhaps the main problem withdesigning a functional wireless battery charging system at this point in time is the limited scope of applications such a technology could be used for. This applies to both standard wireless chargers and versatile Qi charging stations regardless of whether they employ WPC, PMA, or any hybrid charging system.

This isn’t a problem that only wireless battery chargers have but pretty much any inductive-based charging system. It is perhaps for this reason that each new charger that hits the market is usually designed for a limited range of devices and applications. Without a doubt, this is guaranteed to change as new breakthroughs are made with regard to WPC / PMA dual-mode receivers.

The components

The key to an effective wireless battery charging system is in the efficiency of its incorporated components. While you can expect any inductive system to feature a transmitter coil, such a system should also support multi-coil arrays for maximum efficiency. Ideally, this would be driven by separate bridges that are automatically selected for their coupled power.

• Charging transmitter –The charging transmitter should at the very least benefit from an input DC rail of 5 to 19 V, which is typically derived from a USB port or an AC/DC power adapter depending on the system’s designated purpose. Mind you, this can get a lot higher within the optimal parameters but not exactly something you can expect at this point in time.
• Transmitter coil –It is important for the transmitter to employ a powerful coil in order to deliver a steady flow of electromagnetic induction. Know that some transmitters support multi-coil arrays driven by separate bridges which automatically select the highest coupled power in order to then deliver it to the wireless power receiver.
• Receiver –Unlike your average wireless charger, the receiver built into afunctional wireless battery charging system uses diode rectifiers made of FETs for improved efficiency. At the same time, this receiver filters the power through the usage of ceramic output capacitors that are then applied to the battery that’s being charged. This can be done either through a linear stage or through a switching regulator.

Now, it needs to be said that both the transmitter and the receiving battery need to be coupled in a way that allows for an optimal current flow. For this reason, the receiving unit usually has a similar coil to the transmitter in order to collect the incoming power. The receiver can also command the transmitter in order to adjust the charging current or voltage.

Design considerations

It goes without saying that wireless electricity requires a stable platform on both ends, which is why when integrating a wireless charging system into a device, the key is to first decide which power standard would best fit the application. In this respect, a next-level charging system would have to offer both single and dual-mode solutions to maximize interoperability.

• Coil selection –One key element to figuring out the appropriate design is to understand the standards that make good use of the coil itself. The coil in this context has to meet certain input DC voltage and output requirements based on application. It needs to be said, however, that the appropriate coil geometry and coil type are usually the same ones used in the evaluation kit of any particular receiver.
• The interface –It is also important for the system to make use of a flat plastic interface for the receiver’s casing. This has the purpose of ensuring that the charging coils are always facing one another for a steady charge transfer. Know that in this respect, the plastic wall cannot be more than a few millimeters thick as it can otherwise affect the transfer of power over a longer period of time.

Some shielding may be necessary with respect to design so that it reduces noise and EMI pickups occurring inside the device. Furthermore, fuel gauging isn’t usually considered whenintegrating the coils into the wireless battery charging system so there’s a chance that this feature may be supported separately depending on the general design.

Such a system would also incorporate a protective mechanism to automatically detect foreign metallic objects if present in the power transfer path. This is essential for avoiding any potential overheating and to make sure that nothing gets in the way of a steady current transfer. Then again, it can be quite tricky to integrate so many protective subsystems into a fairly peculiar charging assembly.

A multipronged approach to wireless charging

We should point out that wireless battery charging systems aren’t meant to compete with standard Qi chargers but rather to complement them by adding a bit of range and versatility. Seeing how the wireless charging landscape keeps changing more and more with the advent of newer technologies, we may reach a point where regular wireless charging simply isn’t suitable or preferable.

This might happen over time as more and more high-power devices begin incorporating wireless charging capabilities, because let’s face it, your average wireless charger has a fairly limited range of applications at this point. 

In other words, it isn’t obvious that one would eventually have to choose their wireless charging system of choice but rather be pressured into a decision by virtue of hardware limitations.

Last but not least, engineers will eventually have to contend with the fact that different devices require different wireless charging methods. This may eventually lead to the creation of new international standards for certain devices and technologies, standards that are already taking shape with respect to some of the proprietary chargers that reputable manufacturers are working on.