What is Qi Wireless Charging?

Wireless Charging 
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Raghav Kapur - everything RF

Dec 14, 2016

Qi - pronounced as 'CHEE' - is the international standard of wireless charging developed by Wireless Power Consortium for the Near-Field applications. It allows you to wirelessly charge a compatible device's battery by placing it on top of a wireless pad without the need for cables or adaptors.

There are two fundamental technologies which have been used for wireless charging – Inductive Coupling and Magnetic Resonant Coupling. The Qi standard takes advantage of both these technologies.

Inductive charging is great for short distances, usually less than 7 mm. The charge passes between a transmitter and receiver coil placed closely together. The coils must be aligned to make the connection, making this charging technology great for direct-contact applications. Some Qi transmitters use multiple coils in different configurations which eliminate the need to align the charging area.

The Qi Specifications builds on the inductive charging by using resonant wireless charging to charge devices at a greater distance. This technology can be used to charge devices up to a distance of 45 mm. This spatial freedom makes resonant charging perfect for applications such as mounting a charger under a table, desk or embedding technology deeper into a device.

Qi Wireless Charging products use both these technologies to provide an efficient and seamless charging experience.

Key Features of the Latest Qi Wireless Charging Specification:
  • Supports both inductive and resonant charging with a range of up to 45 mm
  • Supports fast charging with the possibility for transmitters/receivers to deliver/receive up to 15 Watts of power (This was 5 Watts in the previous version).
  • Improved thermal test for transmitters
  • Improved Foreign Object Detection – This prevents heating of metal objects in the neighborhood of an active transmitter.
  • Optional unique identifier for power receivers (WP-ID)
  • Increased design freedom for transmitters. You can now choose from over 12 different transmitter specifications

Here are two images that show the same Qi Wireless Charging System using the Inductive and Resonant Coupling modes for two different use cases.


This is the same Qi Wireless Charger with the Receiver receiver separated from the transmitter with a 35mm wooden block