Q-factor determination of coil select
In accordance with embodiments of the present invention, a wireless power transmitter includes a transmit coil that includes a plurality of concentric coils; a switch circuit coupled to the plurality of concentric coils; a driver coupled to provide a voltage to the switch circuit; and a controller coupled to the switch circuit, the controller providing control signals to the switch circuit selecting to provide the voltage across one or more of the plurality of concentric coils depending on a Q-factor measuring in the presence of a receive coil. A method of operating a wireless power transmitter includes determining a measured Q-factor for each of a plurality of configurations of concentric transmit coils; determining a difference between each of the measured Q-factors and a standard Q-factor; and selecting one of the plurality of configurations based on the differences.
1. A wireless power transmitter, comprising:
a transmit coil that includes a plurality of concentric coils;
a switch circuit coupled to the plurality of concentric coils;
a driver coupled to provide a voltage to the switch circuit; and
a controller coupled to the switch circuit, the controller configured to execute instructions to measure a Q-factor for each of the plurality of concentric coils in the presence of a receive coil, determine differences between standard Q-factors for each of the plurality of concentric coils and the measured Q-factor for each of the plurality of concentric coils, determine a coil configuration based on the differences such that the coil configuration includes one of the plurality of concentric coils that has a size less than that of the receive coil and provide control signals to the switch circuit selecting to provide the voltage across one or more of the plurality of concentric coils depending on the coil configuration.
2. The transmitter of claim 1 , wherein each of the plurality of concentric coils is an independent coil.
3. The transmitter of claim 1 , wherein the plurality of concentric coils is coupled in series.
4. The transmitter of claim 1 , wherein the plurality of concentric coils includes an inner coil, a middle coil, and an outer coil.
5. The transmitter of claim 4 , wherein the differences include an inner coil difference, a middle coil difference, and an outer coil difference and the controller determines the configuration of the plurality of concentric coils to use
according to a first condition, a second condition, and a third condition such that the configuration is the inner coil when the first condition is met, the middle coil when the second configuration is met, and the outer coil when the third condition is met.
6. The transmitter of claim 4 , wherein the difference include an inner coil difference, a middle coil difference, and an outer coil difference and the controller determines which of the plurality of concentric coils to use by
selecting the inner coil when the inner coil difference is high, the middle coil difference is low or medium, and the outer coil difference is low;
selecting a series combination of the middle coil and the inner coil when the inner coil difference is high, the middle coil difference is high, and the outer coil difference is low or medium; and
selecting a series combination of the outer coil, the middle coil, and the inner coil when the inner coil difference is high, the middle coil difference is high, and the outer coil difference is high.
7. The transmitter of claim 4 , wherein the inner coil has a diameter appropriate to transfer power to the receive coil of a wearable device, the middle coil has a diameter appropriate to transfer power to the receive coil of a phone, and the outer coil has a diameter appropriate to transfer power to the receive coil of a tablet.
8. A method of operating a wireless power transmitter, comprising:
determining a measured Q-factor for each of a plurality of concentric transmit coils in the presence of a receive coil;
determining a difference between each of the measured Q-factors and a standard Q-factor for each of the plurality of concentric transmit coils;
selecting one of the plurality of configurations based on the differences for each of the plurality of concentric transmit coils such that the coil configuration includes one of the plurality of concentric coils that has a size less than that of the receiver coil; and
providing wireless power using the selected configuration to the receive coil.
9. The method of claim 8 , wherein the plurality of configurations of concentric transmit coils includes a plurality of independently driven concentric coils.
10. The method of claim 8 , wherein the plurality of configurations of concentric transmit coils includes one or more series coupled combinations of a plurality of concentric coils.
11. The method of claim 8 , wherein the plurality of concentric coils includes an inner coil, a middle coil, and an outer coil.
12. The method of claim 11 , wherein the differences include an inner coil difference, a middle coil difference, and an outer coil difference and wherein selecting one of the plurality of configurations includes
selecting the inner coil when a first condition of the inner coil difference, the middle coil difference, and the outer coil difference is determined;
selecting the middle coil when a second condition of the inner coil difference, the middle coil difference, and the outer coil difference is determined; and
selecting the outer coil when a third condition of the inner coil difference, the middle coil difference, and the outer coil difference is determined.
13. The method of claim 11 , wherein the difference includes an inner coil difference, a middle coil difference, and an outer coil difference and wherein selecting one of the plurality of configurations includes
selecting the inner coil when the inner coil difference is high, the middle coil difference is low or medium, and the outer coil difference is low;
selecting a series combination of the middle coil and the inner coil when the inner coil difference is high, the middle coil difference is high, and the outer coil difference is low or medium; and
selecting a series combination of the outer coil, the middle coil, and the inner coil when the inner coil difference is high, the middle coil difference is high, and the outer coil difference is high.
14. The method of claim 11 , wherein the inner coil has a diameter appropriate to transfer power to the receive coil of a wearable device, the middle coil has a diameter appropriate to transfer power to the receive coil of a phone, and the outer coil has a diameter appropriate to transfer power to the receive coil of a tablet.
15. The method of claim 8 , further including
determining whether the one of the plurality of configurations is not appropriate; and
selecting a different configuration of the plurality of configurations if the one of the plurality of configurations is not appropriate.
16. The method of claim 15 , wherein determining includes receiving an actual identification inconsistent with the one of the plurality of configurations.
17. The method of claim 15 , wherein determining that the one of the plurality of configurations is not appropriate when power requirements of a receiver cannot be met.
18. The method of claim 17 , wherein the different configuration includes a next size coil if the power requirements of the receiver cannot be met with the one of the plurality of configurations.