The Importance of Thermal Design in Wireless Charging Devices

14 November, 2017


The advantages of wireless charging are that it’s quicker, easier, and more convenient – just place your device down on top of a charging pad and wait. It offers real benefits in terms of both productivity and efficiency. But while it’s likely to be the next big step in smartphone technology – with brands such as Apple and Samsung building wireless charging capabilities into both the iPhone8 and the S8 this year – it is also expected to present a significant thermal design challenge for future engineers.

Wireless charging uses the principle of Inductive Power Transfer (IPT) - the process of inducing an electromagnetic field by transferring an electrical current between two objects via coils. While this system provides a highly efficient form of charging, it does place two coils – the coil in the phone and the charging pad – in close proximity.

The majority of installed wireless charging systems are built for “regular speed” charging, transferring a maximum of 5W of power to the battery. However, both Apple and Samsung’s smartphones support FastCharge capabilities. Samsung’s Galaxy series allows for 9W quick-charging while the recent iPhone 8 update allows for 7.5W – power levels that will generate a significant amount of heat. As a result, design engineers have a tough challenge to ensure the device does not overheat. 

It’s well known that smartphones, which are often subjected to computationally intense workloads, can heat up quickly – with some processors heating up by more than 30ºC within seconds – before quickly cooling again. The dramatic fluctuation in temperature can result in poor performance and a reduced lifecycle.

This additional heat presents new challenges for product designers. However, for many designers, thermal properties are still largely seen as a secondary design consideration. Faced with widespread demand for wireless charging, device manufacturers may overlook seemingly minor thermal considerations in order to get their products to market. In reality however, these minor considerations can be the difference between a product that works efficiently and a product that burns out after a short amount of time. 

If engineers are to deal with these thermal considerations effectively, they must start to design out potential thermal issues as early on in the design process as possible. According to research from 6SigmaET, only 25% of design engineers are managing thermal issues early on in their designs, while 27% wait until after a design is complete. To make wireless charging a functional reality, engineers must start to fix the potential thermal challenges before they have an opportunity to arise.

As wireless charging is refined over the coming years – and the system’s capabilities increase as it becomes more commonplace – engineers need to shift towards dealing with thermal properties as a priority in the initial design process. 

By: Tom Gregory, Product Manager