Wireless charger, system and method
A wireless charger includes a plurality of charging units for charging wirelessly chargeable devices. Each charging unit includes one or more transmit coils for producing a wireless charging signal. Each charging unit also includes a driver circuit for driving the one or more transmit coils. The driver circuit is switchable according to a charging PWM duty cycle of that charging unit. Each charging unit is operable to perform a Q factor measurement by injecting excitation energy into the one or more transmit coils of that charging unit to produce a free resonance signal, and measuring a decay rate of the free resonance signal. Each charging unit is operable to alter its charging PWM duty cycle during a time window in which another charging unit of the wireless charger is performing a Q factor measurement.
1. A wireless charger for simultaneous wireless charging of multiple wirelessly chargeable devices, the wireless charger comprising:
a plurality of charging units, each charging unit for charging a respective one of the wirelessly chargeable devices, each charging unit comprising:
one or more transmit coils for producing a wireless charging signal; and
a driver circuit for driving the one or more transmit coils of that charging unit, the driver circuit comprising at least one transistor, wherein each transistor is switchable according to a charging pulse width modulation (PWM) duty cycle of that charging unit,
wherein each charging unit is operable to perform a Q factor measurement for measuring a Q factor associated with the one or more transmit coils of that charging unit by:
injecting excitation energy into the one or more transmit coils of that charging unit to produce a free resonance signal; and
measuring a decay rate of the free resonance signal, and wherein each charging unit is operable to alter its charging PWM duty cycle during a time window in which another charging unit of the wireless charger is performing a Q factor measurement, for reducing interference from the wireless charging signal of that charging unit in the free resonance signal produced by the other charging unit.
2. The wireless charger of claim 1 , wherein the time window is in the range 1-200 μs.
3. The wireless charger of claim 1 , wherein each charging unit is operable to alter its charging PWM duty cycle during the time window by reducing the duty cycle.
4. The wireless charger of claim 3 , wherein each charging unit is operable to alter its charging PWM duty cycle during the time window by reducing the duty cycle by at least 50%.
5. The wireless charger of claim 4 , wherein each charging unit is operable to alter its charging PWM duty cycle during the time window by reducing the duty cycle to substantially zero.
6. The wireless charger of claim 1 , wherein each charging unit is operable to increase its charging PWM duty cycle to a predetermined charging PWM duty cycle after the time window has passed.
7. The wireless charger of claim 1 , further comprising circuitry for, while a first charging unit of the wireless charger is performing a Q factor measurement, discharging energy from the one or more transmit coils of each other charging unit of the wireless charger.
8. A wireless charging system comprising a wireless charger according to claim 1 and at least one said wirelessly chargeable device.
9. The wireless charging system of claim 8 , wherein the wirelessly chargeable device includes a capacitor for storing energy to drive charging circuitry of the wirelessly chargeable device during the time window.
10. A wireless charging method for simultaneous charging of wirelessly chargeable devices, the method comprising:
a first charging unit of a wireless charger performing a Q factor measurement for measuring a Q factor associated with one or more transmit coils of that charging unit by:
injecting excitation energy into the one or more transmit coils of that charging unit to produce a free resonance signal; and
measuring a decay rate of the free resonance signal, and
at least one other charging unit of the wireless charger, during a time window in which the first charging unit is performing the Q factor measurement:
altering a charging pulse width modulation (PWM) duty cycle of that charging unit for reducing interference from the wireless charging signal of that charging unit in the free resonance signal produced by the first charging unit.
11. The wireless charging method of claim 10 , wherein the time window is in the range 1-200 μs.
12. The wireless charging method of claim 10 , comprising the at least one other charging unit of the wireless charger altering its charging PWM duty cycle during the time window by reducing the duty cycle.
13. The wireless charging method of claim 12 , comprising the at least one other charging unit of the wireless charger altering its charging PWM duty cycle during the time window by reducing the duty cycle by at least 50%.
14. The wireless charging method of claim 13 , comprising the at least one other charging unit of the wireless charger altering its charging PWM duty cycle during the time window by reducing the duty cycle to substantially zero.
15. The wireless charging method of claim 10 , further comprising discharging energy from the one or more transmit coils of the at least one other charging unit while the first charging unit is performing the Q factor measurement.