In my previous blog I talked about efficiency and using it to measure “how loose” a loosely coupled system actually is. The next question is how much does an end-user actually care about the efficiency of sub 20W consumer device charging solutions. When was the last time you checked the efficiency of your wall wart for your smartphone or your laptop for that matter? Is this data even easily available to curious end-users?
To get an appreciation for how close to the thermal edge smartphones operate at today, you only need to play music or stream a video over 3G / WiFi on a sunny day and see how long it takes before smartphone goes into self-preservation mode. It is said that computer design is more like refrigerator design these days to see who can design the best heat sinks. For a long time Apple did not put i7 processors in their MacBook Pros due to the inability to get heat outside the slick Aluminium shell.
To ensure that wireless charging for consumer devices is widely adopted (such as smartphones & tablets), the technology should not limit the usability of devices while charging is taking place. In my view efficiency is actually a means to achieving thermal performance which is the “end”, and NOT the “end” itself. Other parameters that matter are; cost, Human RF Exposure, EMC performance, Rx size, and how quickly the device charges.