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1. (WO2012145327) WIRELESS POWER TRANSMITTER TUNING
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WHAT IS CLAIMED IS:

1. An apparatus configured to wirelessly provide power to a load, the apparatus comprising:

a transmit circuit comprising a transmit coil, the transmit circuit being configured to wirelessly provide power to the load, the transmit circuit being further configured to resonate at a resonant frequency, the transmit circuit having a reactance;

a detection circuit configured to detect a change in the resonant frequency while providing power to the load; and

a tuning circuit configured to adjust the reactance based on the change.

2. The apparatus of claim 1, further comprising a driver circuit configured to drive the transmit circuit, wherein the detection circuit is configured to detect a change in current through the driver circuit, and wherein the tuning circuit is configured to:

adjust the reactance of the transmit coil to a plurality of reactance values; determine a respective plurality of current values by measuring current through the driver circuit at the plurality of reactance values;

select one of the plurality of reactance values based on the determined current values; and

adjust the reactance of the transmit coil to the selected reactance value.

3. The apparatus of claim 2, wherein the detection circuit is configured to detect an amount of increase in the current.

4. The apparatus of any of claims 1-3, wherein the transmit circuit comprises a reactive element, wherein the tuning circuit comprises a switch in parallel with the reactive element, and wherein the tuning circuit is configured to adjust the reactance of the transmit circuit by opening or closing the switch.

5. The apparatus of claim 4, wherein the switch is positioned at a center tap of the transmit coil

6. The apparatus of claim 4, wherein the reactive element comprises a capacitor.

7. The apparatus of any of claims 1-3, further comprising a parasitic coil inductively coupled to the transmit coil, and wherein the tuning circuit is configured to adjust the reactance by opening or closing a switch of the parasitic coil.

8. The apparatus of any of claims 1-3, further comprising a driver circuit, and wherein the detection circuit is configured to detect an amount of current through the driver circuit to detect a change in the resonant frequency based on the amount of current.

9. The apparatus of any of claims 1-3, wherein the transmit circuit comprises a reactive element, wherein the tuning circuit comprises a two or more transistors, the two or more transistors being in parallel with the reactive element, and wherein the tuning circuit is configured to adjust the reactance of the transmit circuit by enabling the two or more transistors.

10. The apparatus of any of claims 1-3, wherein the transmit circuit is configured to wirelessly provide power to a receive circuit to provide power to the load, the receiver circuit being configured to resonate at the resonant frequency.

11. A method of tuning a wireless power transmitter, the method comprising: detecting a change in a resonant frequency of a transmit circuit comprising a transmit coil of the wireless power transmitter while wirelessly providing power to a first device; and

adjusting a tuning reactance of the transmit circuit based on the detection while wirelessly providing power to the first device.

12. The method of claim 11, wherein detecting a change in the resonant frequency comprises detecting a change in current through a driver circuit of the wireless power transmitter, and wherein adjusting a tuning reactance comprises:

adjusting a reactance of the transmit circuit to a plurality of reactance values;

determining a respective plurality of current values by measuring the current through the driver circuit at the plurality of reactance values;

selecting one of the plurality of reactance values based on the determined current values; and

adjusting the reactance of the transmit circuit to the selected reactance value.

13. The method of claim 12, wherein selecting one of the plurality of reactance comprises selecting based on an amount of increase in the current.

14. The method of any of claims 11-13, wherein adjusting the tuning reactance comprises opening or closing a switch in parallel with a reactive element of the transmit circuit.

15. The method of claim 14, wherein the switch is positioned at a center tap of the transmit coil

16. The method of claim 14, wherein the reactive element comprises a capacitor.

17. The method of any of claims 11-13, wherein adjusting the tuning reactance comprises opening or closing a switch of a parasitic coil circuit inductively coupled to the transmit coil.

18. The method of any of claims 11-13, wherein detecting a change in the resonant frequency comprises detecting an amount of current through a driver circuit and detecting the change in the resonant frequency based on the amount of current.

19. The method of any of claims 11-13, wherein adjusting the tuning reactance comprises enabling two or more transistors, the two or more transistors being in parallel with a reactive element of the transmit circuit.

20. The method of any of claims 11-13, wherein the first device comprises a receive circuit configured to wirelessly receive power from the transmit circuit, the receive circuit being configured to resonate at the resonate frequency.

21. An apparatus configured to wirelessly provide power to a load, the apparatus comprising:

means for wirelessly transmitting power to the load, the means for wirelessly transmitting power being configured to resonate at a resonant frequency, the means for wirelessly transmitting power having a reactance;

means for detecting a change in the resonant frequency while providing power to the load; and

means for tuning configured to adjust the reactance based on the change.

22. The apparatus of claim 21, further comprising means for driving the means for wirelessly transmitting power, wherein the means for detecting is configured to detect a change in current through the means for driving, and wherein the means for tuning is configured to:

adjust the reactance of the means for wirelessly transmitting power to a plurality of reactance values;

determine a respective plurality of current values by measuring current through the means for driving at the plurality of reactance values;

select one of the plurality of reactance values based on the determined current values; and

adjust the reactance of the means for wirelessly transmitting power to the selected reactance value.

23. The apparatus of claim 22, wherein the means for detecting is configured to detect an amount of increase in the current.

24. The apparatus of any of claims 21-23, wherein the means for wirelessly transmitting power comprises a reactive element, wherein the means for tuning comprises a switch in parallel with the reactive element, and wherein the means for tuning is configured to adjust the reactance of the means for wirelessly transmitting power by opening or closing the switch.

25. The apparatus of claim 24, wherein the switch is positioned at a center tap of the means for wirelessly transmitting power

26. The apparatus of claim 24, wherein the reactive element comprises a capacitor.

27. The apparatus of any of claims 21-23, further comprising a means for wirelessly passively relaying power inductively coupled to the means for wirelessly transmitting power, and wherein the means for tuning is configured to adjust the reactance by opening or closing a switch of the means for wirelessly passively relaying power.

28. The apparatus of any of claims 21-23, further comprising a means for driving, and wherein the means for detecting is configured to detect an amount of current through the means for driving to detect a change in the resonant frequency based on the amount of current.

29. The apparatus of any of claims 21-23, wherein the means for wirelessly transmitting power comprises a reactive element, wherein the means for tuning comprises a two or more transistors, the two or more transistors being in parallel with the reactive element, and wherein the means for tuning is configured to adjust the reactance of the transmit circuit by enabling the two or more transistors.

30. The apparatus of any of claims 21-23, wherein the means for wirelessly transmitting is configured to wirelessly provide power to a means for wirelessly receiving to provide power to the load, the means for wirelessly receiving being configured to resonate at the resonant frequency

31. The apparatus of any of claims 21-23, wherein the means for wirelessly transmitting power comprises a transmit circuit comprising a transmit coil.

32. The apparatus of any of claims 21-23, wherein the means for detecting comprises a detection circuit, and wherein the means for tuning comprises a tuning circuit.

33. The apparatus of claim 27, wherein the means for wirelessly passively relaying power comprises a parasitic coil circuit comprising a parasitic coil.

34. The apparatus of claim 30, wherein the means for wirelessly receiving comprises a receive circuit comprising a receive coil.