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Compatibility or freedom?

Qi is about compatibility and design freedom.

Compatibility means that, when you see the Qi logo, you know "this will work".  A mobile product carrying the Qi logo will be powered by all wireless power transmitters that carry the Qi logo.

Design freedom means that manufacturers are not limited in the design of products. Manufacturers must be able to innovate and differentiate their products.

Compatibility is not a natural friend of design freedom. It is really easy to design a wireless battery charger that does not charge a Qi-compatible receiver. It is much harder to make sure that a new transmitter design will work flawlessly with all Qi receivers.

The Wireless Power Consortium has a policy for dealing with the trade-off between design freedom and compatibility:

  1. Compatibility is king. The message of the Qi logo is: "it will work".
  2. Design freedom for power receivers has priority. We give receivers priority because Qi adoption in mobile products drives the market for wireless chargers.

The first version of the Qi specification delivers the intended design freedom for receivers. You can see that already in our demonstrations: Qi receivers have been built into batteries, phones, Bluetooth headsets, sleeves, ...

There are more requirements for transmitters, but the range of possible transmitters is significant. The first version of the Qi specification allows four types of transmitters. Two multi-coil arrays, a moving coil, and fxed single coil transmitters. And each type allows different shapes and sizes where manufacturers can make their own trade off between cost, user experience, and design. That is already quite a bit of design freedom.

We are now increasing the freedom in transmitter design even further. Members of the consortium have proposed new transmitter types. These new types are added to the specification when we are certain that the new transmitter will not break the compatibility rule. The procedure for adding a new transmitter looks straightforward but is quite a lot of work:

  1. The new transmitter must pass the certification tests described in part 3 of the specification.
  2. The new transmitter must meet the performance requirements described in part 2 of the specification
  3. The new transmitter must work flawlessly with all previously certified receivers.
  4. The new transmitter must not reduce the design freedom of receivers.

Step 4 of the procedure is the tricky part. How can you be sure that some future receiver does not break compatibility with this new transmitter type? Interoperability with the previously certified receivers and conformity with the certification tests (Steps 1 & 3) are a good indication, but not enough. In Step 4 we challenge the reviewers of the proposed new transmitter type to come up with exotic receiver designs that will work with the current transmitter types but fail with the new transmitter type. When the reviewers fail, the new transmitter passes.

When can you expect new transmitter types in future updates of the Qi specification? I will announce that when the update is ready!

Do you want to add a transmitter design of your own? Follow the procedure! Members of the wireless power consortium can find a more detailed description of this procedure on the member's section of the website.

Compatibility or freedom?