Leave your cables at home
Wireless charging eliminates the cable typically required to charge wearable devices, mobile phones and cordless appliances. With a wireless charger, the battery inside any battery-powered appliance can be charged by simply placing the appliance close to a wireless power transmitter or a designated charging station. Tightly coupled wireless charging technology uses magnetic induction to transfer power from a transmitter (Tx) in the charging station to a receiver (Rx). The magnetic field is generated by a coil on the TX side. The field is captured by a coil on the RX side. Inductive charging typically operates over distances of up to 4 cm (1.6 inches).
Why support wireless charging?
Wireless charging is convenient with no cables to connect. But the real benefit to wireless charging, which mechanical designers realize and others not so much yet, is that with wireless charging you can fully seal a product. You can make the case completely sealed to keep water or other liquids from getting in so it can be used outdoors. For example, if you can drop it in water, as long as the enclosure is fully sealed. Embed a battery, put in a wireless charger, and it’s fully protected product. Wireless charging is great for implanted devices or any device that needs to be sterilized with chemicals.
Wireless charging is also convenient. You simply place the device on the charger instead of plugging in a cable. It is particularly important for implanted devices where it is the only option other than removing the device to charge or replace a battery.
Wireless charging standards
There are two major wireless charging standards that have emerged in the last few years, Qi and AirPower. Apple’s AirPower standard can be used by multiple devices at once and may soon be incorporated into the Qi-standard. Older standards include Rezence, WiPower, PMA, and Open Dots.
Qi is fairly universal and there are lots of chips that support it. Additionally, there are lots of wireless Qi charging pads, so we like to design using the Qi standard.
Sometimes the application requirements do not allow the use of a mat or a wireless charging pad available off-the-shelf, and in those cases we design a custom charging station.
A number of semiconductor companies offer Qi chipsets. Popular ones are
- ST STWLC33
- NXP MWPR1516
- TI BQ51013B
- IDT P9225
Wireless charging limitations
The device must be very close to the charger. There has been a lot of work on long distance charging but it is not available for real products. Proper design is necessary so that the device is properly placed on the charger. If the device is not oriented correctly (for example on its side at right angles to the pad), it will not charge properly. The design of the device and the charger must make it difficult to orient the device incorrectly on the charger. Another limitation is that it may be necessary to carry a charger when traveling. Wireless chargers are bulkier than other chargers.
Let’s us know if you have a device that would benefit from adding wireless charging.