1111111111111111 IIIIII IIIII 11111 1111111111 11111 111111111111111 IIIII IIIII 1111111111 11111111
`US 20080079392Al
`
`c19) United States
`c12) Patent Application Publication
`Baarman et al.
`
`c10) Pub. No.: US 2008/0079392 Al
`Apr. 3, 2008
`(43) Pub. Date:
`
`(54) SYSTEM AND METHOD FOR INDUCTIVELY
`CHARGING A BATTERY
`
`(22) Filed:
`
`Sep. 14, 2007
`Related U.S. Application Data
`
`(75)
`
`Inventors:
`
`David W. Baarman, Fennville, MI
`(US); John James Lord,
`Springfield, IL (US); Nathan P.
`Stien, West Des Moines, IA (US)
`
`Correspondence Address:
`WARNER, NORCROSS & JUDD
`IN RE: ALTICOR INC.
`INTELLECTUAL PROPERTY GROUP, 111
`LYON STREET, N. W. STE 900
`GRAND RAPIDS, MI 49503-2489
`
`(73) Assignee:
`
`ACCESS BUSINESS GROUP
`INTERNATIONAL LLC, Ada,
`MI (US)
`
`(21) Appl. No.:
`
`11/855,710
`
`(60) Provisional application No. 60/827,586, filed on Sep.
`29, 2006.
`Publication Classification
`
`(51)
`
`Int. Cl.
`H02J 7100
`(2006.01)
`(2006.01)
`H0JM 10144
`(52) U.S. Cl. ........................................ 320/108; 320/137
`ABSTRACT
`(57)
`
`An inductive charging system for recharging a battery. The
`system includes a charger circuit and a secondary circuit.
`The secondary circuit includes a feedback mechanism to
`provide feedback to the charger circuit through the inductive
`coupling of the primary coil and the secondary coil. The
`charger circuit includes a frequency control mechanism for
`controlling the frequency of the power applied to the pri(cid:173)
`mary coil at least partly in response to the feedback from the
`feedback mechanism.
`
`--~~ :
`~~-~
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`1----------1 Oscilator
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`64
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`
`Over voltage
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`
`38
`
`84Jl4a -------------------------------------
`
`8
`
`Ex.1012
`APPLE INC. / Page 1 of 14
`
`

`

`Patent Application Publication
`
`Apr. 3, 2008 Sheet 1 of 7
`
`US 2008/0079392 Al
`
`100
`% CHARGE
`DELIVERED
`
`1 :
`
`CELL
`VOLTAGE
`
`CHARGE
`RATE
`
`0
`1.. Constant
`Current
`
`_J___I ~i~~~I ======-i-1
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`FIG. 3
`
`Ex.1012
`APPLE INC. / Page 2 of 14
`
`

`

`Patent Application Publication
`
`Apr. 3, 2008 Sheet 2 of 7
`
`US 2008/0079392 Al
`
`23
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`
`L _______________________________________ _
`
`FIG. 2
`
`Ex.1012
`APPLE INC. / Page 3 of 14
`
`

`

`Patent Application Publication
`
`Apr. 3, 2008 Sheet 3 of 7
`
`US 2008/0079392 Al
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`Ex.1012
`APPLE INC. / Page 4 of 14
`
`

`

`Patent Application Publication
`
`Apr. 3, 2008 Sheet 4 of 7
`
`US 2008/0079392 Al
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`Ex.1012
`APPLE INC. / Page 5 of 14
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`Ex.1012
`APPLE INC. / Page 6 of 14
`
`

`

`Patent Application Publication
`
`Apr. 3, 2008 Sheet 6 of 7
`
`US 2008/0079392 Al
`
`~ 1 .55
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`
`Ex.1012
`APPLE INC. / Page 7 of 14
`
`

`

`Patent Application Publication
`
`Apr. 3, 2008 Sheet 7 of 7
`
`US 2008/0079392 Al
`
`10
`
`Start
`
`I
`I
`I
`
`I
`
`r------------- ---------------------------------------7
`:
`102
`Wait for PROBE_INTERVALi----~---~
`104
`
`Energize primary coil at
`PROBE_FREQUENCY
`
`Detect primary current
`through coil
`
`106
`
`108
`
`99-,
`
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`
`109
`
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`132
`.-----~'1'-----------+o-ils there feedback? No
`
`Is primary current>unloaded
`primary current?
`
`No
`
`Clear
`CHARGED_FLAG
`
`134
`
`Is CHARGED_FLAG set?
`
`Yes
`
`Set CHARGED_FLAG
`
`No
`
`111
`
`110
`
`Set OP _FREQ=FREQ_START
`
`Yes
`No
`Is ChARGE_ TIME<
`118
`112
`MIN_CHARGE_ TIME?
`,---- ---- ----------------------------- --------7
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`L _________ ---------------------------,------- __ J
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`+2*AFREQ
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`
`116
`
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`124
`130 126
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`Is there feedback?t----~ :
`Long charge delay
`L-----------------------------------------~
`
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`
`FIG. 7
`
`Delay
`
`128
`
`Ex.1012
`APPLE INC. / Page 8 of 14
`
`

`

`US 2008/0079392 Al
`
`Apr. 3, 2008
`
`1
`
`SYSTEM AND METHOD FOR INDUCTIVELY
`CHARGING A BATTERY
`
`BACKGROUND OF THE INVENTION
`
`[0001] Charging of batteries with an inductive power
`supply is well-known. Inductive charging of batteries for
`electric automobiles as well as the charging of small electric
`appliance batteries such as those for toothbrushes has met
`some amount of success. Because inductive charging does
`not require a physical connection between the battery and
`the charger, the charging is considerably more convenient.
`However, not all batteries are easily charged inductively.
`Lithium-ion batteries (Li-Ion) are one such type of battery.
`[0002] Recharging Li-Ion batteries is not as straightfor(cid:173)
`ward as that of other batteries. Li-Ion batteries are unable to
`absorb an overcharge. If a constant current is applied to a
`fully charged Li-Ion battery, metallic lithium plating may
`develop which could lead to failure of the battery. Thus, care
`should be taken not to overcharge the battery.
`[0003] Conversely, charging a Li-Ion battery to full capac(cid:173)
`ity presents some difficulty. The maximum voltage of a
`Li-Ion battery can be attained relatively quickly during
`recharging by applying a constant current to the battery.
`However, when the Li-Ion battery reaches a maximum
`voltage, the Li-Ion battery may not be fully charged. Without
`further charging, the battery will only be approximately 65%
`charged. If a constant current is continually applied to the
`battery after the battery has reached its maximum voltage,
`then the battery could be overcharged, which could lead to
`premature battery failure.
`[0004] Conventional battery chargers have been devel(cid:173)
`oped to fully charge a Li-Ion battery. Generally, the battery
`charger uses a constant current, constant voltage schema to
`charge the battery. A discharged battery is first charged at a
`constant current level in the range of 0.1 C to 1 C amperes,
`where C is the battery capacity in amp-hours, until the
`battery reaches the desired voltage of about 4.2 volts. At this
`point, the battery charger switches to a constant voltage
`mode, providing the sufficient power to maintain the battery
`at this final voltage while providing additional charging to
`the battery.
`[0005] The charging profile for a typical Li-Ion battery is
`shown in FIG. 1. A constant current is applied for a prede(cid:173)
`termined period. During this phase, the charging of the
`Li-Ion battery is generally constant. For a typical battery,
`this phase lasts somewhat less than one hour. The Li-Ion
`battery eventually exhibits a constant voltage near a pre(cid:173)
`ferred voltage prior to attaining a full charge. A constant
`voltage is then applied to the Li-Ion battery. After approxi(cid:173)
`mately an hour of charging with a constant voltage, the
`battery has typically attained its maximum charge.
`[0006]
`If the charging ofa Li-Ion battery does not follow
`the charging profile shown in FIG. 1, then there is a risk that
`the battery will not be fully charged or that the charging will
`damage the battery.
`[0007] The charging of a Li-Ion battery is further compli(cid:173)
`cated because the battery is often not fully discharged before
`charging. If some residual charge remains on the battery,
`then optimal charging may require some amount of constant
`current charging followed by constant voltage charging, or,
`alternatively, the optimal charging may require only constant
`voltage charging. For better performance, the battery
`charger should provide a mechanism for compensating for
`the charge state of the battery.
`
`[0008] Charging Li-Ion batteries is especially problematic
`where inductive charging is used. In an inductive battery
`charger, a primary coil located in the charger provides power
`to an inductive secondary located in the battery. The voltage
`across the secondary is then rectified and applied to the
`battery to recharge the battery. There is no direct physical
`connection between the battery and the battery charger.
`Because there is no physical connection between the battery
`and the battery charger, information regarding the state of
`the battery is not readily available to the battery charger.
`[0009] At the same time, portable devices need to be
`lightweight. Thus, complex circuitry to monitor the charge
`state of the battery and relay that information to the induc(cid:173)
`tive charger increases the cost, size and weight of the
`portable device.
`[0010] An inductive system capable of charging a battery
`having a unique charge cycle while using a relatively simple
`circuit directly coupled to the battery is highly desirable.
`
`SUMMARY OF THE INVENTION
`
`[0011] An inductive system for recharging a battery, such
`as a Li-Ion battery, having a unique charging cycle generally
`includes a charger circuit having a primary coil for induc(cid:173)
`tively supplying charging power and a secondary circuit for
`inductively receiving the charging power and applying that
`power to a battery. The secondary circuit includes a feed(cid:173)
`back mechanism to provide feedback to the charger circuit
`through the inductive coupling of the primary coil and the
`secondary coil. The charger circuit includes a frequency
`control mechanism for controlling the frequency of the
`power applied to the primary coil at least partly in response
`to the feedback from the feedback mechanism.
`[0012]
`In one embodiment, the feedback mechanism
`includes a subcircuit for varying the reflected impedance of
`the secondary circuit. In this embodiment, the charger circuit
`may include a feedback detector for monitoring a charac(cid:173)
`teristic of the power in the charger circuit that varies at least
`in part in response to changes in the reflected impedance of
`the secondary circuit. In this embodiment, the feedback
`detector may be coupled to the primary coil to allow the
`controller to monitor the current through the primary coil.
`[0013]
`In one embodiment, the feedback mechanism
`includes an over-voltage detector or an over-current detec(cid:173)
`tor, or both. In this embodiment, the detectors may be
`arranged so as to control one or more switches, such as
`transistors. If either an over-voltage condition or an over(cid:173)
`current condition is detected in the secondary circuit, then
`the switch is turned on and the current from the secondary
`coil is shunted from the battery through a resistor. In this
`way, the battery is protected from significant exposure to
`over-voltage or over-current conditions. The feedback
`mechanism may be directly coupled to the battery.
`[0014]
`In one embodiment, the feedback detector is a
`current sensor coupled to the primary tank circuit. In this
`embodiment, when the current is shunted through the feed(cid:173)
`back signaling resistor in the secondary, the current through
`the secondary coil increases, which varies the reflected
`impedance of the secondary circuit resulting in increased
`current through the primary coil. The increase in current
`through the primary coil is detected by the current sensor in
`the primary circuit, which could include a peak detector,
`thereby providing to the controller a feedback signal for
`detecting whether the battery is in an over-voltage or over(cid:173)
`current state. In one embodiment, the frequency control
`
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`Apr. 3, 2008
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`2
`
`mechanism makes appropriate adjustments to the frequency
`to correct the over-voltage or over-current state by reducing
`the power supplied to the secondary coil.
`[0015]
`In one embodiment, the charger circuit includes an
`inverter and a tank circuit. In this embodiment, the operating
`frequency of the inverter is reduced to move the frequency
`of the power applied to the primary coil closer to the
`resonant frequency of the tank circuit, while the operating
`frequency of the inverter is increased in order to move the
`frequency of the power applied to the primary coil away
`from the resonant frequency of the tank circuit. It would be
`equally possible to arrange the system such that an increase
`in the inverter frequency would move the power applied to
`the primary coil closer to resonance and thereby increase
`power transfer while a decrease in inverter frequency would
`move the power applied to the primary coil farther from the
`resonant frequency of the tank circuit and thereby decrease
`the power transfer.
`[0016]
`In another aspect, the present invention also pro(cid:173)
`vides a method for operating an inductive charging system
`having a charger circuit with a primary coil and a secondary
`circuit with a secondary coil. The method generally includes
`the steps of detecting whether a battery is present in the
`secondary circuit and charging the battery by way of one or
`more charging cycles. The charging step generally includes
`the steps of: applying power to a primary coil at a frequency,
`evaluating feedback from the secondary circuit through the
`primary coil and secondary coil inductive coupling and
`adjusting the frequency of the power applied to the primary
`coil as a function of the feedback from the secondary circuit.
`In this way, the frequency of the power applied to the
`primary coil is changed in order to optimize the charging for
`the battery. Several charging cycles may be necessary to
`fully charge the battery.
`[0017]
`In one embodiment, the method is utilized with a
`charger circuit having a tank circuit. In this embodiment, the
`charging cycle may include the alternative steps of moving
`the power applied to the primary coil closer to the resonant
`frequency of the tank circuit or moving the power applied to
`the primary coil farther from the resonant frequency of the
`tank circuit. The charger circuit may include an inverter. In
`such embodiments, the steps of moving the frequency of the
`power applied to the primary coil may be further defined as
`moving the operating frequency of the inverter.
`[0018]
`In one embodiment, the charging step generally
`includes the steps of: applying power to the primary coil at
`a specific frequency; determining whether a feedback signal
`from the charger circuit is received by the charger circuit;
`and varying the frequency of the power applied to the
`primary coil as a function of the feedback signal to either
`increase or decrease the power delivered to the secondary
`circuit. In one embodiment, the step of varying the fre(cid:173)
`quency is further defined as including the steps of: moving
`the frequency of the power applied to the primary coil
`farther from resonance if a feedback signal from the feed(cid:173)
`back mechanism is received or moving the frequency of the
`power applied to the primary coil closer to resonance if a
`feedback signal from the feedback mechanism is not
`received.
`[0019]
`In one embodiment, the charging step generally
`includes the steps of incrementally moving the frequency of
`the power applied to the primary coil closer to resonance
`until a feedback signal is received; after a feedback signal is
`received, incrementally moving the frequency of the power
`
`applied to primary close farther from resonance until a
`feedback signal is no longer received; and applying power to
`the primary coil at the frequency for a charging period. The
`process may be repeated.
`[0020]
`In one embodiment, the step of determining
`whether a feedback signal is received includes the steps of
`sensing the current in the charger circuit and comparing the
`sensed current with a predetermined threshold.
`[0021]
`In one embodiment, the method further includes
`the step of terminating the charging cycle when the time for
`completing one charging cycle is less then a minimum
`charging cycle time. The method may further include the
`step of terminating the charging cycle when the frequency of
`the power applied to the primary coil meets an upper and/or
`lower threshold.
`[0022]
`In one embodiment, the detecting step further
`includes the steps of: applying a pulse of power to the
`primary coil at a predetermined probe frequency, sensing the
`reflected impedance, and determining whether a battery is
`present as a function of the sensed reflected impedance.
`[0023] The present invention provides a simple and effec(cid:173)
`tive inductive charging circuit that permits nonlinear charg(cid:173)
`ing profiles to be implemented in an inductive system with
`a small number of components. The over-current and over(cid:173)
`voltage detectors not only provide feedback used to drive the
`frequency of the charging power, but also protect the battery
`from potential harmful power conditions. The charging
`profile can be easily changed by varying a number of stored
`values that dictate operation of the system. The present
`invention is well-suited for use in charging portable elec(cid:173)
`tronic devices, such as cell phones, personal digital assis(cid:173)
`tants, handheld gaming devices, personal media players and
`other similar devices. In this context, the secondary circuit
`may be incorporated into the portable electronic device so
`that the device can be placed in close proximity to the
`charger circuit for charging, thereby eliminating the need to
`plug the device into a charger.
`[0024] These and other objects, advantages, and features
`of the invention will be more fully understood and appre(cid:173)
`ciated by reference to the description of the current embodi(cid:173)
`ment and the drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0025] FIG. 1 shows the charging profile for a typical
`Li-Ion battery;
`[0026] FIG. 2 shows a system for inductive charging of a
`battery;
`[0027] FIG. 3 is a power transfer curve between a primary
`coil and a secondary coil;
`[0028] FIG. 4 shows a circuit diagram corresponding to
`the block diagram of FIG. 2 for the charger circuit;
`[0029] FIG. 5 shows a circuit diagram corresponding to
`the block diagram of FIG. 2 for the battery side;
`[0030] FIG. 6 shows the output of the peak detector caused
`by the increased current through the secondary coil; and
`[0031] FIG. 7 is a flow chart for a method of operating a
`battery charger.
`
`DESCRIPTION OF THE CURRENT
`EMBODIMENT
`
`[0032] An inductive charging system in accordance with
`an embodiment of the present invention in shown in FIG. 2.
`The inductive charging system 4 is configured to inductively
`
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`Apr. 3, 2008
`
`3
`
`charge a battery having a nonlinear charging profile, such as
`a Li-Ion battery. The system 4 generally includes a charger
`circuit 6 and secondary circuit 8. The charger circuit 6
`generally includes a primary coil 15, a frequency controller
`80 for applying power to the primary coil at a desired
`frequency and a feedback detector 82 for receiving feedback
`from the secondary circuit 8. The secondary circuit 8 gen(cid:173)
`erally includes a secondary coil 30 for receiving inductive
`power from the charger circuit 6 and a feedback mechanism
`84 for providing feedback to the charger circuit 6 indicative
`of the voltage or current in the secondary circuit 8. The
`frequency controller 80 varies the frequency of the power
`applied to the primary coil 15 as a function of the feedback
`from the secondary circuit 8. Although described in connec(cid:173)
`tion with the charging of a conventional Li-Ion battery, the
`present invention is well suited for use in charging other
`types of batteries, including batteries having different charg(cid:173)
`ing profiles.
`[0033] As noted above, the charger circuit 6 generally
`includes a frequency controller 80, a primary coil 15, and a
`feedback detector 82. In the illustrated embodiment, the
`frequency controller 80 includes a controller 20, an oscilla(cid:173)
`tor 18, a driver 16 and an inverter 10. In this embodiment,
`these components collectively drive a tank circuit 12. More
`specifically, the inverter 10 provides AC (alternating cur(cid:173)
`rent) power to the tank circuit 12 from a source of DC ( direct
`current) power 14. The tank circuit 12 includes the primary
`coil 15. The tank circuit 12 may be either a series resonant
`tank circuit or a parallel resonant tank circuit. Tn this
`embodiment, the driver 16 provides the signals necessary to
`operate the switches within the inverter 10. The driver 16 in
`turn operates at a frequency set by the oscillator 18. The
`oscillator 18 is, in turn, controlled by the controller 20. The
`controller 20 could be a microcontroller, such as a
`PIC18LF1320, or a more general purpose microprocessor.
`Although shown as essentially discrete devices in the illus(cid:173)
`trated embodiment, the driver 16, oscillator 18 and could
`alternatively be integrated and could be implemented as
`modules within the controller 20.
`[0034]
`In the illustrated embodiment, the feedback detec(cid:173)
`tor 82 detects the current in the tank circuit 12. In operation,
`the controller 20 uses signals from the peak detector 22 to
`assist in determining the frequency of operation for the
`oscillator 18, and thereby the frequency of the inverter 10.
`Although the feedback detector 82 of the illustrated embodi(cid:173)
`ment detects current in the tank circuit 12, other character(cid:173)
`istics of the power in the charger circuit 6 may be evaluated
`to provide charge information regarding the battery.
`[0035] The secondary circuit 8 generally includes a sec(cid:173)
`ondary coil 30, a rectifier 32, and a feedback mechanism 84.
`The secondary coil 30 inductively receives power from the
`primary coil 15. The rectifier 32 provides DC power to
`charge the battery 34. In this embodiment, the feedback
`mechanism 84 is configured to provide feedback when the
`current applied to the battery 34 exceeds a threshold value
`or when the voltage applied to the battery 34 exceeds a
`threshold value. As shown, the feedback mechanism of this
`embodiment generally includes an over-voltage detector 36,
`an over-current detector 40, an OR gate 38, a switch 42, and
`a resistor 44. The output of an over-voltage detector 36
`indicates whether the voltage across the battery 34 is above
`a predetermined level. Similarly, the output of an over(cid:173)
`current detector 40 indicates whether the current to the
`battery 34 is above a predetermined amount. The output of
`
`the current detector 40 as well as the output of the voltage
`detector 36 are coupled to the inputs of an OR gate 38. The
`OR gate 38 could be a discrete circuit, or it could be a
`connection between the outputs of the detectors. The output
`of the OR gate 38 is coupled to the switch 42. The switch 42
`is controlled by the output of the OR gate 38 and is
`connected in series between the rectifier 32 and the resistor
`44. The switch 42 could be any suitable switch such as a
`bipolar transistor, a field effect transistor, or an insulated gate
`bipolar transistor. The resistor 44 is connected in series
`between the switch 42 and ground.
`[0036]
`In operation, if the output of the over-voltage
`detector 36 or the output of the over-current detector 40
`indicate an over-voltage or an over-current situation, then
`the output of the OR gate 38 turns on the switch 42. When
`the switch 42 is on, current from the rectifier 32 flows
`through the resistor 44 to ground.
`[0037] Because the impedance of the resistor 44 is much
`less than the impedance of the battery 34, a current surge
`occurs through the resistor 44, thereby causing a current
`surge through the secondary coil 30. The diode 64 prevents
`the battery 34 from supplying any current when the switch
`42 is turned on. The current surge through the secondary coil
`30 creates a similar current surge in the charger circuit 6
`through the primary coil 15. The current surge is detected by
`the peak detector 22. The controller 20 then changes the
`frequency of the oscillator 18.
`[0038]
`In the illustrated embodiment, the primary coil 15
`and the secondary coil 30 are loosely coupled. Because the
`two are loosely coupled in this embodiment, the slope of the
`power transfer curve about the resonant frequency is not as
`steep as if the coils 15, 30 were tightly coupled. An exem(cid:173)
`plary power transfer curve for the coils 15, 30 is shown in
`FIG. 3. In this embodiment, the power transfer is highest
`when the inverter 10 is operating at resonance. However,
`even if the inverter 10 is not operating at resonance, sig(cid:173)
`nificant power transfer can occur when the inverter is
`operating off-resonance. Generally, the inverter 10 is oper(cid:173)
`ated between frequency A and frequency B. Frequency B is
`somewhat less than the resonant frequency. Between fre(cid:173)
`quency A and frequency B, the power transfer curve can be
`piece-wise linearized by a software lookup table located in
`the controller 20. Thus, a decrease in the operating fre(cid:173)
`quency of the inverter 10 will result in a generally predict(cid:173)
`able increase in the power transferred from the primary coil
`15 to the secondary coil 30. As can be seen by the graph, it
`would be equally effective to use an operating frequency less
`than the resonant frequency. If so, then an increase in the
`operating frequency would lead to an increase in the power
`transfer, and vice-versa.
`[0039] FIG. 4 shows a circuit diagram corresponding to
`the block diagram of FIG. 2 for the charger circuit 6 of the
`system. The peak detector 22 (comprised of 22A and 22B)
`is connected in series with the primary coil 15 and provides
`a signal by way of the transformer 50 that is proportional to
`the current through the primary coil 15. The signal is
`rectified by a diode 52 and then used to charge capacitor 54.
`The operational amplifiers 56, 58 are used to smooth the
`signal for sampling by the controller 20. This particular
`circuit diagram is exemplary and is not intended to limit the
`scope of the invention to a specific circuit design.
`[0040] FIG. 5 shows a circuit diagram for the secondary
`circuit 8 of the system. As with the charger circuit diagram
`of FIG. 4, the secondary circuit diagram of FIG. 5 is
`
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`Apr. 3, 2008
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`4
`
`exemplary and not intended to limit the scope of the inven(cid:173)
`tion to a specific circuit design. Power from the secondary
`coil 30 is used to charge capacitor 60, which in tum is used
`as the power supply for the circuitry connected to the battery
`34. A rectifier 32 produces a DC current from the AC current
`supplied by secondary coil 30. A capacitor 62 is charged to
`provide a DC power source for charging the battery 34. A
`blocking diode 64 prevents the battery 34 from discharging
`when the secondary coil 30 is not receiving power or when
`the feedback mechanism is signaling an over-voltage or
`over-current condition.
`If either the over-voltage detector 36 or the over(cid:173)
`[0041]
`current detector 40 determines that too much voltage or too
`much current is applied to the battery 34, then the transistor
`42 is turned on, thereby discharging the capacitor 62 through
`the resistor 44, resulting in a lower voltage across the battery
`34. In this embodiment, the secondary circuit 8 includes a