Method and apparatus for wirelessly charging portable electronic devices

• US 10,164,472 B2
• Filed: 11/19/2014
• Issued: 12/25/2018
• Est. Priority Date: 12/03/2013
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Chandrakasan, Anantha, Jin, Rui
• Primary Examiner(s): Tra, Quan
• Application Number:
  US14/911,599
• Publication Number:
  US 20160268832A1
• Time in Patent Office: 1,497 Days
• Field of Search: 307104
• CPC Class Codes: H02J 50/10 using inductive coupling
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/40 using two or more transmitting or receiving devices H02J50/50 takes precedence
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0013 acting upon several batteries simultaneously or sequentially H02J7/1423 takes precedence
• CPC Class Codes: H02J 7/342 The other DC source being a battery actively interacting with the first one, i.e. battery to battery charging with circuits for polarity protection H02J7/0034
• CPC Class Codes: H03F 2200/451 the amplifier being a radio frequency amplifier
• CPC Class Codes: H03F 3/19 with semiconductor devices only
• CPC Class Codes: H03F 3/2176 Class E amplifiers
• CPC Class Codes: H04B 1/3883 Arrangements for mounting batteries or battery chargers

Abstract

Wireless charging of portable electronic devices is carried out by detecting load variations caused by the device and dynamically compensating for these variations during charging to increase system efficiency and regulate delivered power. In some embodiments, load variations are tracked by comparing a feedback signal to a value range and determining whether the feedback value is higher than, lower than, or within the range of values. This information is then used to modify one or more parameters associated with a power amplifier in a transmitter device.

Claims

1. A portable electronic device that is capable of charging other portable electronic devices, the portable electronic device comprising:

a battery terminal for connection to a battery;

a class-E power amplifier coupled to the battery terminal, the class-E power amplifier having a switching transistor and a resonant circuit, the resonant circuit having at least one variable shunt capacitance and at least one variable inductance, the at least one variable inductance for magnetic coupling to a coil within an external portable device to be charged, wherein the at least one variable inductance in the first portable electronic device and the coil in the external portable device form a transformer between the devices during a charging operation, wherein a load of the external portable device is reflected into the portable electronic device through the transformer;

comparison circuitry to determine whether a voltage across an output of the switching transistor is above, below, or within a predetermined voltage range at a particular point within a switching cycle of the switching transistor of the class-E power amplifier; and

compensation circuitry to adjust the at least one variable shunt capacitance and the at least one variable inductance if the comparison circuitry determines that the voltage across the output of the switching transistor is above or below the predetermined voltage range, wherein the compensation circuitry is configured to perform no adjustment to the at least one variable shunt capacitance and the least one variable inductance if the comparison circuitry determines that the voltage across the output of the switching transistor is within the predetermined voltage range; and

wherein;

the comparison circuitry is configured to sample the voltage across the output of the switching transistor just before the transistor turns back on during the switching cycle, wherein the comparison circuitry is synchronized to the switching frequency of the switching transistor but samples at a lower rate.

2. The portable electronic device of claim 1, wherein:

at least one variable shunt capacitance and the at least one variable inductance of the resonant circuit are capable of switching between a predetermined number of capacitance-inductance value pairs that have a particular order, wherein the compensation circuitry is configured to activate a next capacitance-inductance value pair in the order if the comparison circuitry determines that the voltage across the output of the switching transistor is above the predetermined voltage range and the compensation circuitry is configured to activate a previous capacitance-inductance value pair in the order if the comparison circuitry determines that the voltage across the output of the switching transistor is below the predetermined voltage range.

3. The portable electronic device of claim 1, wherein:

the compensation circuitry is configured to adjust the capacitance value of the at least one variable shunt capacitance and the inductance value of the at least one variable inductance in a continual manner to dynamically compensate for changes in primary side load in the portable electronic device.

4. The portable electronic device of claim 1, wherein:

the portable electronic device is configured to cease charging another portable electronic device when the other portable electronic device has reached a predetermined level of charging that is less than a maximum level of charging.

5. The portable electronic device of claim 1, wherein:

the external portable device includes one of the following;

a wearable electronic device, a wireless accessory, and a medical implant.

6. The portable electronic device of claim 1, wherein:

the external portable device includes one of the following;

a smart wristband, a smart watch, a smart glove, a bicycle light, a portable multi-media player, a wireless input/output device, a pager, and a cochlear implant.

7. The portable electronic device of claim 1, wherein:

the power amplifier circuitry is configured to convert a DC voltage from the battery to a radio frequency (RF) signal to generate a time varying current within the at least one variable inductance.

8. The portable electronic device of claim 1, wherein:

the portable electronic device includes a cellular telephone.

9. The portable electronic device of claim 1, wherein:

the comparison circuitry and the compensation circuitry are configured to operate continually during charging operations to compensate for time varying load.

10. The portable electronic device of claim 1, wherein:

the compensation circuit includes at least one comparator to compare the switch voltage to first and second reference voltages which define the predetermined voltage range.

11. The portable electronic device of claim 10, wherein:

at least one of the comparison and compensation circuitry includes logic circuitry to process the output of the at least one comparator to determine whether the switch voltage is higher than, lower than, or within a voltage range defined by the first and second reference voltages and to generate the control signals based thereon.

12. The portable electronic device of claim 10, wherein:

the comparison and compensation circuitry are configured to adjust the at least one variable shunt capacitance and the at least one variable inductance, based on the comparison, in a manner that maintains approximately zero switch turn-on voltage to achieve enhanced efficiency and to regulate the power delivered to the external portable device.

13. The portable electronic device of claim 1 wherein:

the at least one variable shunt capacitance and the at least one variable inductance of the resonant circuit includes a set of discrete capacitors and a multi-tapped transmit coil, respectively, the set of discrete capacitors and a multi-tapped transmit coil having N switchable capacitance-inductance value pairs, wherein N is a positive integer greater than 1.

14. The electronic device of claim 1 wherein the class-E power amplifier is configured to use energy from the battery to wirelessly charge the external portable device during charging operations.

15. The electronic device of claim 1 wherein the voltage across the output of the switching transistor corresponds to a feedback voltage of the class-E power amplifier measured at a time just before the switch turns on during a switching cycle.