Systems and methods of detecting a change in object presence in a magnetic field

• US 9,912,201 B2
• Filed: 04/11/2011
• Issued: 03/06/2018
• Est. Priority Date: 04/11/2011
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Oettinger, Eric Gregory
• Primary Examiner(s): Henze-Gongola, David V
• Application Number:
  US13/084,510
• Publication Number:
  US 20120256620A1
• Time in Patent Office: 2,521 Days
• Field of Search: 320108, 307104
• CPC Class Codes: G01R 33/0041 using feed-back or modulation techniques
• CPC Class Codes: G01R 33/028 Electrodynamic magnetometers
• CPC Class Codes: H01F 38/14 Inductive couplings for wireless supply or distribution of electric power using inductive coupling H02J50/10
• CPC Class Codes: H02J 50/10 using inductive coupling
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/90 involving detection or optimisation of position, e.g. alignment
• CPC Class Codes: H02J 7/0049 Detection of fully charged condition
• CPC Class Codes: H04B 5/26 using coils
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer

Abstract

The systems and methods of detecting a change in object presence in a magnetic field disclosed herein inject a low amplitude signal near the resonant frequency into the coil until the system comes to equilibrium. At this point the feedback is measured. The feedback signal can be measured as at least one of several signals, for example, but not limited to the voltage on the resonant capacitor, the current in the coil, and the voltage between the resonant capacitor and the coil. A change in the steady state response indicates a change in device presence.

Claims

1. A method of operating a wireless charging circuit determining change in object presence in a magnetic field comprising:

during a time period in which the wireless charging circuit does not deliver power to a load, driving a primary coil with an injected signal at a substantially constant frequency to create a magnetic field, the injected signal being at a substantially lower duty cycle signal than a signal used to transmit power;

measuring passively generated effects on amplitude of a feedback signal during a driving phase of the injected signal after the signal reaches a steady-state;

monitoring the passively generated effects;

determining a change in object presence in the magnetic field emitted from the primary coil based on a comparison of the monitored passively generated effects with a previous determination of the passively generated effects, the determination being absence of a receiver, presence of a non-receiver object or presence of a receiver in the magnetic field, wherein object detection is determined before charging a device in the magnetic field is initiated; and

further comprising sampling the passively generated monitored effects substantially synchronously to the injected signal in at least two points, at least one point having a phase difference of substantially 180 degrees with respect to the injected signal and another point having a phase difference of substantially 90 degrees with respect to the injected signal.

2. The method of claim 1, wherein the injected signal is an analog signal transmitted from the primary coil at substantially a resonant frequency.

3. The method of claim 2, wherein the monitored passively generated effects are in response to the transmitting of the analog signal.

4. The method of claim 1, wherein the sampling is performed after the sampled effects have reached a steady state condition.

5. The method of claim 1, wherein the monitored passively generated effects are detected on at least one of:

voltage on a resonant capacitor, current in the primary coil, and voltage node between the resonant capacitor and the primary coil.

6. A wireless charging system comprising:

a charger for providing power at a first amplitude to a receiver comprising;

a power control circuit;

a primary coil driven by an injected signal from the power control circuit at a substantially constant frequency at a second amplitude less than the first amplitude and insufficient for power delivery to operate a receiver to create a magnetic field and configured to measure amplitude of passively generated effects on a feedback signal during a driving phase of the injected signal after the signal reaches a steady-state; and

a controller configured to compare the measured amplitude of the feedback signal with passively generated effects in a previous measurement and to determine a change in presence of an object in the magnetic field emitted from the primary coil, the determination being absence of a receiver, presence of a non-receiver object or presence of a receiver in the magnetic field, wherein object detection is determined before charging a device in the magnetic field is initiated;

wherein the measured passively generated effects are sampled substantially synchronously with the injected signal in at least two points one point having a substantially 180 degree phase difference with respect to the injected signal and another point having a phase difference of substantially 90 degree with respect to the injected signal.

7. The wireless charging system of claim 6, wherein the injected signal is an analog signal transmitted from the primary coil at substantially a resonant frequency of the primary coil.

8. The wireless charging system of claim 7, wherein the measured passively generated effects are a response to the analog signal.

9. The wireless charging system of claim 6, wherein the sampling is performed after the sampled effects have reached a steady state condition.