Detection of device removal from a surface of a multi-coil wireless charging device
Systems, methods and apparatus for wireless charging are disclosed. A charging device has a plurality of charging cells provided on a charging surface, a charging circuit and a controller. The controller may be configured to cause the charging circuit to provide a charging current to a resonant circuit when a receiving device is placed on the charging surface, provide a measurement slot by causing the charging circuit to decrease or terminate the charging current for a period of time and determine whether the receiving device has been removed from the charging surface based on measurement of a characteristic of the resonant circuit during the measurement slot. The characteristic of the resonant circuit may be representative of electromagnetic coupling between a transmitting coil in the resonant circuit and a receiving coil in the receiving device.
1. A method for operating a charging device, comprising:
transferring power to a receiving device in accordance with a charging configuration, including providing a charging current to a resonant circuit according to the charging configuration, the charging configuration being generated after determining that the receiving device has been placed at a first location on a charging surface of the charging device;
detecting a change or rate of change in voltage or current level in the resonant circuit while transferring power to the receiving device;
initiating a measurement slot by terminating the charging current for a period of time after detecting the change or rate of change in the voltage or current level;
determining, during the measurement slot, whether the receiving device has been moved away from the first location;
resuming power transfer to the receiving device in accordance with the charging configuration by resuming the charging current to the resonant circuit when the receiving device remains at the first location; and
discontinuing power transfer to the receiving device after determining that the receiving device has been moved away from the first location.
2. The method of claim 1 , wherein determining whether the receiving device has been moved away from the charging surface comprises:
performing a passive ping or digital ping procedure after initiating the measurement slot.
3. The method of claim 1 , wherein determining whether the receiving device has been moved away from the charging surface comprises:
determining whether Q-factor of the resonant circuit has changed with respect to a reference Q-factor.
4. The method of claim 1 , wherein determining whether the receiving device has been moved away from the charging surface comprises:
determining that a step change in the voltage or current level in the resonant circuit exceeds a threshold value.
5. A non-transitory processor-readable storage medium having instructions stored thereon which, when executed by at least one processor of a charging circuit in a charging device, cause the charging circuit to:
cause the charging circuit to transfer power to a receiving device in accordance with a charging configuration, including by providing a charging current to a resonant circuit when the receiving device has been placed at a first location on a charging surface of the charging device;
detect a change or rate of change in voltage or current level associated with the resonant circuit while transferring power to the receiving device;
initiate a measurement slot by terminating the charging current for a period of time after the change or rate of change in the voltage or current level is detected;
perform a passive ping or digital ping procedure after initiating the measurement slot;
determine whether the receiving device has been removed from the charging surface based on a change in Q-factor of the resonant circuit determined using measurements obtained during the measurement slot;
cause the charging circuit to resume power transfer to the receiving device in accordance with the charging configuration by resuming the charging current to the resonant circuit when the Q-factor of the resonant circuit indicates that the receiving device remains on the charging surface; and
cause the charging circuit to discontinue power transfer to the receiving device after determining that the receiving device has been moved from the first location.
6. A non-transitory processor-readable storage medium having instructions stored thereon which, when executed by at least one processor of a charging circuit in a charging device, cause the charging circuit to:
cause the charging circuit to transfer power to a receiving device in accordance with a charging configuration, including by providing a charging current to a resonant circuit when the receiving device has been placed at a first location on a charging surface of the charging device;
detect a change or rate of change in voltage or current level associated with the resonant circuit while transferring power to the receiving device;
initiate a measurement slot by causing the charging circuit to terminate the charging current for a period of time after the change or rate of change in the voltage or current level is detected;
detect a change or rate of change in voltage or current associated with the resonant circuit after initiating the measurement slot; and
determine that the receiving device has been removed from the charging surface when a step change in the voltage or current associated with the resonant circuit exceeds a threshold value.