USOO8129864B2
`
`(12) United States Patent
`Baarman et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,129,864 B2
`Mar. 6, 2012
`
`(54)
`
`(75)
`
`(73)
`
`(*)
`
`(21)
`(22)
`(65)
`
`(60)
`
`(51)
`
`(52)
`(58)
`
`(56)
`
`INDUCTIVE POWER SUPPLY WITH IDUTY
`CYCLE CONTROL
`
`Inventors: David W. Baarman, Fennville, MI (US);
`Scott A. Mollema, Rockford, MI (US);
`Joshua K. Schwannecke, Portland, MI
`(US); Thomas Jay Leppien, Grand
`Haven, MI (US); Kenneth Michael
`Burns, North Canton, OH (US)
`Assignee: Access Business Group International
`LLC, Ada, MI (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 208 days.
`Appl. No.: 12/349,840
`
`Notice:
`
`Filed:
`
`Jan. 7, 2009
`
`Prior Publication Data
`US 2009/O174263 A1
`Jul. 9, 2009
`
`Related U.S. Application Data
`Provisional application No. 61/019,411, filed on Jan.
`7, 2008.
`
`Int. C.
`(2006.01)
`HOIF 27/42
`U.S. Cl. ....................................................... 307/104
`Field of Classification Search .................. 307/104;
`713/300,320, 320/108
`See application file for complete search history.
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`4,076,966 A
`2f1978 Bovo et al.
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`
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`6,271,508 B1
`8/2001 Thompson et al.
`(Continued)
`
`EP
`
`FOREIGN PATENT DOCUMENTS
`O267009
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`(Continued)
`
`OTHER PUBLICATIONS
`International Search Report and Written Opinion of the International
`Searching Authority in the Counterpart PCT Application, dated May
`4, 2009.
`
`(Continued)
`Primary Examiner – Albert W Paladini
`(74) Attorney, Agent, or Firm — Warner Norcross & Judd
`LLP
`
`ABSTRACT
`(57)
`An inductive power Supply that maintains resonance and
`adjusts duty cycle based on feedback from a secondary cir
`cuit. A controller, driver circuit and Switching circuit cooper
`ate to generate an AC signal at a selected operating frequency
`and duty cycle. The AC signal is applied to the tank circuit to
`create an inductive field for powering the secondary. The
`secondary communicates feedback about the received power
`back to the primary controller. The power transfer efficiency
`may be optimized by maintaining the operating frequency
`Substantially at resonance, and the amount of power trans
`ferred may be controlled by adjusting the duty cycle.
`
`35 Claims, 10 Drawing Sheets
`
`124
`
`/
`
`WIRELESS
`RECEIVER
`
`OO
`
`115
`
`112
`111
`AA.
`A.
`l-1 DRIVER H SWITCH
`
`
`
`116
`
`CONTROLLER
`
`) N DRIVER
`110
`ity-------------.
`
`SWITCH
`--------------- V
`
`
`
`TANK
`CIRCUIT
`
`CURRENT
`SENSOR
`
`.../
`
`Ex.1009
`APPLE INC. / Page 1 of 19
`
`

`

`US 8,129,864 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`6,316,756 B1
`1 1/2001 Thompson et al.
`6,348,679 B1
`2/2002 Ryan et al.
`6,359,267 B1
`3, 2002 Wilcox et al.
`6,515,878 B1* 2/2003 Meins et al. .................... 363/37
`6,521,874 B2
`2/2003 Thompson et al.
`6,529,127 B2 * 3/2003 Townsend et al. ............ 340/.505
`6,600,142 B2
`7/2003 Ryan et al.
`6,617,557 B1
`9/2003 Ryan et al.
`6,649.888 B2 11/2003 Ryan et al.
`6,664,881 B1
`12/2003 Thompson et al.
`6,727,482 B2
`4/2004 Bassill et al.
`6,730,894 B2
`5/2004 Thompson et al.
`6,812,445 B2 11/2004 Gorbold
`6.825,620 B2 11/2004 Kuennen et al.
`6,861,629 B2
`3/2005 Dahake et al.
`6,912,137 B2
`6/2005 Berghegger
`6,934,167 B2 * 8/2005 Jang et al. .................. 363.21.02
`6,995,345 B2
`2/2006 Gorbold
`7,180,248 B2
`2/2007 Kuennen et al.
`7,208,912 B2
`4/2007 Ghabra et al.
`7.212,414 B2
`5/2007 Baarman ......................... 363/16
`7,279.665 B2 * 10/2007 Kagan ........................... 219,661
`7,385,357 B2
`6/2008 Kuennen et al.
`7,489,530 B2
`2/2009 Paull
`7,551,011 B2
`6, 2009 Paul1
`7,579,715 B2 * 8/2009 Seelig et al. .................... 307/75
`7,602,142 B2 * 10/2009 Weber et al. .................. 320, 108
`7,626.463 B2 12, 2009 Paul1
`7,804,045 B2
`9, 2010 Rosenbloom et al.
`
`2003/02101.06 A1 11/2003 Cheng et al.
`38885 A.
`1439 San Fulos et al.
`2004/O130916 A1
`7/2004 Baarman
`2004/O145342 A1
`7/2004 Lvon
`56
`ics. A
`75, Ran
`2007/0182367 A1
`8, 2007 PartOvi
`2010, 0123451 A1
`5, 2010 Freer
`2010.0171367 A1
`7, 2010 Kitamura et al.
`FOREIGN PATENT DOCUMENTS
`12097.91
`11, 2001
`12097.91
`5, 2002
`09-103037
`4f1997
`HO9-149565
`6, 1997
`H111881.13
`7, 1999
`2001.23372
`8, 2001
`9428560
`12/1994
`96.05648
`2, 1996
`96.17499
`6, 1996
`OO54387
`9, 2000
`2004O73 150
`8, 2004
`2005122686
`12/2005
`2008137996
`11, 2008
`
`EP
`EP
`JP
`JP
`JP
`JP
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`
`OTHER PUBLICATIONS
`
`US 4,658,187, 04/1987, Grubbs (withdrawn)
`* cited by examiner
`
`Ex.1009
`APPLE INC. / Page 2 of 19
`
`

`

`U.S. Patent
`
`Mar. 6, 2012
`
`Sheet 1 of 10
`
`US 8,129,864 B2
`
`124
`
`1 OO
`
`WIRELESS
`RECEIVER
`
`DRIVER
`
`SWITCH
`
`CONTROLLER
`
`CIRCUIT
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`110
`
`
`
`DRIVER H SWITCH
`
`-----
`
`CURRENT
`SENSOR
`
`Fig. 1
`
`122
`
`Ex.1009
`APPLE INC. / Page 3 of 19
`
`

`

`U.S. Patent
`
`Mar. 6, 2012
`
`Sheet 2 of 10
`
`US 8,129,864 B2
`
`2OO
`
`226
`
`WRELESS
`TRANSMITTER
`
`222
`
`
`
`CONTROLLER
`
`SIGNAL
`RECEIVER
`
`212
`
`CURRENT
`SENSOR
`
`VOLTAGE
`SENSOR
`
`RECTFER
`
`SWITCH
`
`
`
`
`
`SECONDARY
`
`21 O
`
`216
`
`Fig.2
`
`Ex.1009
`APPLE INC. / Page 4 of 19
`
`

`

`U.S. Patent
`
`Mar.6, 2012
`
`Sheet 3 of 10
`
`US 8,129,864 B2
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`Ex.1009
`APPLEINC./ Page 5 of 19
`
`Ex.1009
`APPLE INC. / Page 5 of 19
`
`

`

`U.S. Patent
`
`Mar.6, 2012
`
`Sheet 4 of 10
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`US 8,129,864 B2
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`APPLE INC. / Page 6 of 19
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`

`

`U.S. Patent
`
`Mar. 6, 2012
`
`Sheet 5 of 10
`
`US 8,129,864 B2
`
`
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`
`Ex.1009
`APPLE INC. / Page 7 of 19
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`

`

`U.S. Patent
`
`Mar. 6, 2012
`
`Sheet 6 of 10
`
`US 8,129,864 B2
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`Ex.1009
`APPLE INC. / Page 8 of 19
`
`

`

`U.S. Patent
`
`Mar. 6, 2012
`
`Sheet 7 of 10
`
`US 8,129,864 B2
`
`0
`
`
`
`Ex.1009
`APPLE INC. / Page 9 of 19
`
`

`

`U.S. Patent
`
`Mar. 6, 2012
`
`Sheet 8 of 10
`
`US 8,129,864 B2
`
`
`
`SET INITIAL
`OPERATING
`FREQUENCY
`
`SET INITIAL
`DUTY CYCLE
`
`ADJUST
`OPERATING
`FREOUENCY
`
`INCREASE
`DUTY CYCLE
`
`Fig.5
`
`DECREASE
`DUTY CYCLE
`
`Ex.1009
`APPLE INC. / Page 10 of 19
`
`

`

`U.S. Patent
`
`Mar. 6, 2012
`
`Sheet 9 of 10
`
`US 8,129,864 B2
`
`6O2
`
`INCREASE
`OPERATING
`FREOUENCY
`
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`EFFICIENCY
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`FREOUENCY
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`FREOUENCY
`
`61 O
`
`Fig.6
`
`Ex.1009
`APPLE INC. / Page 11 of 19
`
`

`

`U.S. Patent
`
`Mar. 6, 2012
`
`Sheet 10 of 10
`
`US 8,129,864 B2
`
`8O
`
`70
`
`60
`
`50
`
`40
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`30
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`
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`SWITCH'ON'
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`SWITCH "OFF"
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`SWITCH "ON"
`
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`SWITCH 'OFF'
`
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`
`INCREASED ON TIME
`
`REDUCED ON TIME
`
`Fig.8
`
`Ex.1009
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`
`

`

`1.
`INDUCTIVE POWER SUPPLY WITH IDUTY
`CYCLE CONTROL
`
`US 8,129,864 B2
`
`This application claims the benefit of U.S. Provisional
`Application No. 61/019,411, filed on Jan. 7, 2008.
`The present invention relates to inductive power and more
`particularly to a system and method for wirelessly supplying
`power.
`
`BACKGROUND OF THE INVENTION
`
`10
`
`In recent years, wireless power Supply systems have
`received increased attention because of some of their benefits
`over traditional wired power Supply systems. Some more
`basic wireless power Supply systems are specifically
`designed to charge a particular device, which can help mini
`mize power transfer efficiency issues. Other wireless power
`Supply systems attempt to account for misalignment, charge
`different remote devices and provide different amounts of
`power. In these systems, maintaining an acceptable power
`transfer efficiency can be difficult.
`Some wireless power systems adjust the operating fre
`quency of an AC signal across the tank circuit closer to or
`further from resonance to increase or decrease the amount of
`power delivered to the remote device. Other wireless power
`systems adjust the resonant frequency of the tank circuit
`closer to or further from the operating frequency. One issue
`with these systems is that the power transfer efficiency
`between the inductive power supply and the remote device is
`a function of how close the operating frequency is to reso
`nance. So, while adjusting the operating frequency or reso
`nant frequency can provide some control over the amount of
`power delivered to the remote device, it may come at the cost
`of decreased power transfer efficiency.
`Other wireless power Supplies use a fixed operating fre
`quency and instead adjust the rail Voltage, duty cycle, orphase
`of the AC signal across the tank circuit to increase or decrease
`the amount of power delivered to the remote device. One issue
`with this is that in order for the power transfer efficiency to be
`acceptable, the inductive power Supply and remote device
`may need to be precisely aligned and specifically designed to
`work with each other.
`
`15
`
`25
`
`30
`
`35
`
`40
`
`SUMMARY OF THE INVENTION
`
`45
`
`The present invention provides an inductive power Supply
`that maintains resonance and adjusts duty cycle based on
`feedback from a secondary circuit. In one embodiment, the
`inductive power Supply includes a primary controller, a driver
`circuit, a Switching circuit, and a tank circuit. The controller,
`driver circuit and Switching circuit cooperate to generate an
`AC signal at a selected operating frequency and duty cycle.
`The AC signal is applied to the tank circuit to create an
`inductive field for powering the secondary. The secondary
`communicates feedback about the received powerback to the
`primary controller. The power transfer efficiency may be
`optimized by maintaining the operating frequency Substan
`tially at resonance, and the amount of power transferred may
`be controlled by adjusting the duty cycle.
`In one embodiment, the secondary circuit includes a sec
`ondary, a rectifier, a Switch, a load, a sensor, a secondary
`controller, and a communication means. A voltage and/or
`current sensor detects characteristics about the power which
`are transmitted back to the primary controller using the com
`munication means. Optionally, over-Voltage and over-current
`65
`protection may be provided. If a fault condition is detected the
`load is disconnected using the Switch.
`
`50
`
`55
`
`60
`
`2
`In one embodiment, a process for inductively powering a
`load by maintaining Substantial resonance and adjusting duty
`cycle is provided. Initially an operating frequency and duty
`cycle are set to an acceptable value. The initial operating
`frequency is determined by Sweeping a range of frequencies
`and selecting the operating frequency which provided the
`highest power transfer efficiency. The initial duty cycle is set
`to a relatively low value, such as 20%, to ensure that too much
`power is not delivered to the secondary. Once the initial
`values have been set, the inductive power Supply enters a
`continuous process of adjusting the operating frequency to
`maintain Substantial resonance and adjusting the duty cycle
`depending on whether the amount of power is too high or too
`low or temperature is too high.
`The present invention provides a simple and effective sys
`tem and method for providing a selected amount of wireless
`power while maintaining a high transfer efficiency. Adjust
`ment of duty cycle provides another level of control of wire
`less power transfer, one which can be used to fine tune the
`amount of power provided to a secondary. Additionally, the
`ability to adjust the amount of power being transferred while
`maintaining Substantial resonance results in fewer overall
`losses and easier fulfillment of specified power requirements.
`These and other objects, advantages, and features of the
`invention will be readily understood and appreciated by ref
`erence to the detailed description of the current embodiment
`and the drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of an inductive power Supply.
`FIG. 2 is a block diagram of a secondary circuit.
`FIGS. 3A-3D together are a circuit diagram of an inductive
`power Supply.
`FIG. 4 is a circuit diagram of a secondary circuit.
`FIG.5 is a flowchart of a process to maintain resonance and
`adjust duty cycle.
`FIG. 6 is a flowchart of a process to adjust the operating
`frequency to maintain resonance.
`FIG. 7 is an exemplary graph showing frequency versus
`power transfer efficiency.
`FIG. 8 is a timing diagram showing a varying duty cycle.
`
`DESCRIPTION OF THE CURRENT
`EMBODIMENT
`
`I. Overview
`
`An inductive power Supply or primary circuit in accor
`dance with an embodiment of the present invention is shown
`in FIG. 1, and generally designated 100. The primary circuit
`100 includes a primary controller 110, a driver circuit 111
`including a pair of drivers 112, 114, a switching circuit 115
`including a pair of switches 116, 118, a tank circuit 120 a
`primary sensor 122 and an optional wireless receiver 124. The
`primary controller 110, driver circuit 111 and the switching
`circuit 115 together generate an AC signal at a selected fre
`quency and selected duty cycle that is applied to the tank
`circuit 120 to create an inductive field for transferring power
`wirelessly to a secondary circuit. A secondary circuit in
`accordance with an embodiment of the present invention is
`shown in FIG. 2, and generally designated 200. The second
`ary circuit 200 may include a secondary 210, a rectifier 212,
`a switch 214, a load 216, a current sensor 218 or voltage
`sensor 220, a secondary controller 222, a signal resistor 224
`for communicating using reflected impedance and an
`optional wireless transmitter 226.
`
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`

`US 8,129,864 B2
`
`3
`In operation, an embodiment of the process for adjusting
`the duty cycle is shown in FIG. 5, the initial operating fre
`quency is set Substantially at resonant frequency 504 and the
`initial duty cycle is set at a relatively low value 506. The
`primary controller continuously adjusts the operating fre
`quency 508 to maintain Substantially resonant frequency and
`continuously determines if the amount of power being trans
`ferred is too high 510. If too much power is being provided or
`temperatures are above a preset threshold then the duty cycle
`is decreased 514. If too little power is being provided then the
`duty cycle is increased 512. Various conditions may tempo
`rarily or permanently reduce or halt the power transfer.
`II. Inductive Power Supply
`
`4
`refers to the number of repetitions per unit time of a complete
`waveform. Duty cycle refers to the proportion of time during
`which the waveform is high compared to the total amount of
`time for a complete waveform. Thus, a square wave as shown
`in FIG. 8, may be described by its frequency and its duty
`cycle. Further, the duty cycle may be adjusted while main
`taining the same frequency and the frequency may be
`adjusted while maintaining the same duty cycle. The driver
`circuit 316 of the illustrated embodiment includes two sepa
`rate drivers and may include additional circuit components to
`boost and filter the signal. For example, in the current
`embodiment, the signal is boosted to 20 volts, without effect
`ing the timing of the signal.
`The switching circuit 318 includes two switches. In the
`current embodiment, the switches are implemented as MOS
`field effect transistors. In alternative embodiments, other cir
`cuit components may be used to implement the Switching
`circuit. Additionally, depending on power requirements
`MOSFETs with different characteristics may be imple
`mented during manufacture. In some embodiments, multiple
`sets of switches may be provided on the circuit board, allow
`ing one set of Switches to be soldered at the time of manufac
`ture based on the particular power requirements of that appli
`cation.
`In one embodiment, the switching circuit 115 includes two
`separate switches 116, 118 that are switched on at the same
`frequency, but out of phase with each other. FIG. 8 illustrates
`the timing for one embodiment of Such a Switching circuit. In
`FIG. 8, both switches have the same duty cycle, but are shifted
`in time from each other by half of the period of the switching
`waveform. In alternative embodiments, each Switch may have
`a different duty cycle and they the switches may be shifted in
`time a different amount from each other. That is, half period
`separation and similar duty cycle are desirable, but unneces
`sary, for the Switches because it may result in increased power
`transfer efficiency from the inductive power supply to the
`remote device.
`The tank circuit 320 generally includes the primary and a
`capacitor. The primary of the current embodiment is an air
`core coil inductor. A cored inductor can also be used if the
`proper considerations are made for spatial freedom, monitor
`ing overall power, and feedback. The capacitance of the
`capacitor may be selected to balance the impedance of the
`primary coil at anticipated operating parameters. In the cur
`rent embodiment, although three tank capacitors are shown,
`all three capacitors need not necessarily be soldered into the
`circuit at the time of manufacture. An inductive power Supply
`may be fabricated which at the time of soldering can have an
`appropriate capacitance value selected by Soldering or
`switching different capacitors into the circuit. The tank circuit
`320 may be either a series resonant tank circuit (as shown in
`FIG. 3D) or a parallel resonant tank circuit (not shown). The
`present invention may be incorporated into the adaptive
`inductive power supply shown in U.S. Pat. No. 6,825,620,
`which is incorporated herein by reference. As another
`example, the present invention may be incorporated into the
`adaptive inductive power supply shown in U.S. Patent Appli
`cation Publication US2004/130916A1 to Baarman, which is
`entitled Adapted Inductive Power Supply’ and was pub
`lished on Jul. 8, 2004 (U.S. Ser. No. 10/689,499, filed on Oct.
`20, 2003), which is also incorporated herein by reference.
`Further, it may be desirable to use the present invention in
`connection with an adaptive inductive power Supply capable
`of establishing wireless communications with the remote
`device. Such as the adaptive inductive power Supply shown in
`U.S. Patent Application Publication US 2004/130915A1 to
`Baarman, which is entitled "Adapted Inductive Power Supply
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`The present invention is suitable for use with a wide variety
`of inductive power supplies. As used herein, the term “induc
`tive power supply” is intended to broadly include any induc
`tive power supply capable of providing power wirelessly. The
`present invention is also suitable for use with “adaptive induc
`tive power supplies.” As used herein, the term “adaptive
`inductive power supply’ is intended to broadly include any
`inductive power Supply capable of providing power wire
`lessly at a plurality of different frequencies. For purposes of
`disclosure, the present invention is described in connection
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`with a particular adaptive inductive power Supply, shown in
`FIGS. 3A-3D and generally designated 300. The illustrated
`adaptive inductive power supply 300 is merely exemplary,
`however, and the present invention may be implemented with
`essentially any inductive power Supply that can be modified to
`provide inductive power at varying duty cycles.
`In the illustrated embodiment, the adaptive inductive
`power supply 300 generally includes a primary controller
`310, a low voltage power supply 312, memory 314, a driver
`circuit 316, a switching circuit 318 a tank circuit 320, a
`current sensor 322, a filter 324 and optionally a wireless
`receiver 326. In operation, the primary controller 310, driver
`circuit 316 and switching circuit 318 apply power to the tank
`circuit 320 to generate a source of electromagnetic inductive
`power at a selected frequency and a selected duty cycle.
`The primary controller 310 of the illustrated embodiment
`includes two microcontrollers, one to control the frequency
`and one to control the duty cycle. The frequency microcon
`troller may be a microcontroller, such as a PIC24FJ32GA002,
`or a more general purpose microprocessor. The duty cycle
`microcontroller may be a microcontroller, such as a
`dsPIC30F2020, or a more general purpose microprocessor. In
`alternative embodiments, the primary controller 310 may be
`implemented using a single microcomputer, FPGA, analog or
`digital circuit. The driver circuit 316 may be discrete compo
`nents, as shown in FIG. 3D, or they may be incorporated into
`the primary controller 310. An oscillator (not shown) may be
`included within the primary controller 310.
`The primary circuit 300 may also include a low voltage
`power Supply 312 for Supplying low Voltage power to the
`primary controller 310, the driver circuit as well as any other
`components requiring low Voltage powerfor operation. In the
`illustrated embodiment the low voltage power supply 312
`provides scales the input voltage to 3.3 volts. In alternative
`embodiments, a different voltage may be provided.
`In the current embodiment, the various components of the
`primary circuit 310 collectively drive the tank circuit 320 at a
`frequency and duty cycle dictated by the primary controller
`310. More specifically, the primary controller 310 controls
`the timing of the driver circuit 316 and switching circuit 318.
`The timing refers to both the frequency and duty cycle of the
`signal being generated. Frequency as it is being used here
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`5
`with Communication' and was published on Jul. 8, 2004
`(U.S. Ser. No. 10/689,148, filed on Oct. 20, 2003), which is
`incorporated herein by reference. Further yet, it may be desir
`able to use the present invention with a printed circuit board
`coil. Such as a printed circuit board coil incorporating the
`invention principles of U.S. Ser. No. 60/975,953, which is
`entitled “Printed Circuit Board Coil” and filed on Sep. 28,
`2007 by Baarman et al, and which is incorporated herein by
`reference in its entirety. In other alternative embodiments, the
`inductor may be implemented as a multi-tap inductor and/or
`the capacitors may be implemented as a Switched capacitor
`bank that may be used to dynamically, before or during use,
`alter the resonance of the primary circuit, for example, as
`described in U.S. Pat. No. 7.212,414, which is entitled "Adap
`tive Inductive Power Supply’ and issued May 1, 2007, to
`Baarman, which is herein incorporated by reference.
`In certain modes of operation, the primary controller 310
`may establish the operating frequency as a function of input
`from the current sensor 322. The controller 310, in turn,
`operates the driver circuit 318 at the frequency established by
`the primary controller 310. The driver circuit 316 provides the
`signals necessary to operate the Switching circuit 318. As a
`result, the switching circuit 318 provides AC (alternating
`current) power to the tank circuit 320 from a source of DC
`(direct current) power. In an alternative embodiment, the
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`operating frequency is established from a separate commu
`nication link, such as the wireless receiver 326, implemented
`in the current embodiment as an IR receiver.
`The primary controller 310 may also establish the duty
`cycle as a function of input from the current sensor 322.
`Planned shunting of the signal resistor on the secondary,
`which will be described in more detail below, may be used to
`provide information to the primary using reflected impedance
`detected with the current sensor 322. Alternatively, the duty
`cycle may be established using a separate communication
`link, such as the wireless receiver 326, implemented in the
`current embodiment as an IR receiver. This could also be near
`field or other RF communication channels.
`In the illustrated embodiment, the current sensor 322 is a
`current transformer having a primary coil connected to the
`tank circuit and a secondary coil connected to the primary
`controller 310. In the current embodiment, the current sensor
`322 includes circuitry to adjust the gain of the output of the
`current sensor to accommodate the ranges accepted by the
`primary controller 310. Further, the amount of gain may be
`adjusted by the primary controller 310 by applying a signal to
`the switch. The inductive power supply 300 may include
`conditioning circuitry 324 for conditioning the current trans
`former output before it is supplied to the primary controller
`310. In the current embodiment, the conditioning circuitry
`324 is a 5KHZ2-pole filter. Although the illustrated embodi
`ment includes a current transformer for sensing the reflected
`impedance of the secondary or remote device, the inductive
`power supply 300 may include essentially any alternative
`type of sensor capable of providing information regarding
`reflected impedance from the secondary 400. Further,
`although the current sensor 322 of the illustrated embodiment
`is connected directly to the tank circuit, the current sensor (or
`other reflected impedance sensor) can be located in essen
`tially any location where it is capable of providing readings
`indicative of the reflected impedance.
`In the illustrated embodiment, the inductive power supply
`300 further includes a memory 314 capable of storing infor
`mation relating to the operating parameters of a plurality of
`secondaries 400. The stored information may be used to per
`mit the inductive power supply 300 to more efficiently power
`the secondary 400 and more readily recognize fault condi
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`US 8,129,864 B2
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`tions. In some applications, the inductive power supply 300
`may be intended for use with a specific set of secondaries 400.
`In these applications, the memory 314 includes the unique
`resonant frequency (or pattern of frequencies) for each sec
`ondary 400, along with the desired collection of associated
`information, such as maximum and minimum operating fre
`quencies, current usage and minimum and maximum duty
`cycle. The memory 314 may, however, include essentially any
`information that may be useful to the inductive power supply
`300 in operating the secondary 400. For example, in applica
`tions where it is desirable to establish wireless communica
`tions with the secondary 400, the memory 314 may include
`information regarding the wireless communication protocol
`of the remote device 400.
`
`III. Secondary Circuit
`
`The present invention is intended for use with a wide vari
`ety of remote devices or secondaries of varying designs and
`constructions. It is anticipated that these various remote
`devices will require power at varying frequency and will have
`different power requirements.
`For purposes of disclosure, one embodiment of a second
`ary circuit 400 is shown in FIG. 4. In the embodiment of FIG.
`4, the secondary circuit 400 generally includes a secondary
`410 for receiving power from the inductive power supply 300,
`a rectifier 414 (or other components for converting AC power
`to DC), a low voltage power supply 412 that scales the
`received power to operate the secondary controller 428, con
`ditioning circuitry 416, 426 to remove ripple in the signal,
`current sensor 418, voltage sensor 422, switch 420, load 424,
`secondary controller 428, a signal resistor 432 and an optional
`wireless transmitter 430. In operation, the rectifier 414 con
`verts the AC power generated in the secondary 410 to DC
`power, which is typically needed to power the load. Alterna
`tively, multiple secondary coils receiving power on different
`phases can be used to reduce the ripple Voltage. This is ref
`erenced in Application Ser. No. 60/976,137, entitled Mul
`tiphase Inductive Power Supply System to Baarman et al.
`which is herein incorporated by reference. Multiple primary
`coils may be desired to transmit power on different phases in
`Such an embodiment. In one embodiment, the load is a charg
`ing circuit (not shown) for a battery. Charging circuits are
`well-known and are widely used with a variety of recharge
`able electronic devices. If desired, the charging circuit may be
`configured to both charge a battery (not shown) and/or power
`the load 424. In alternative embodiments the rectifier may be
`unnecessary and AC power may be conditioned to be used to
`power the load.
`The current sensor 418 detects the amount of current in the
`received power and provides that information to the second
`ary controller 428. The voltage sensor 422 detects the amount
`of voltage in the received power and provides that informa
`tion to the secondary controller 428. Although the illustrated
`embodiment includes both a Voltage sensor 422 and a current
`sensor 418, only one is necessary. By sensing the Voltage
`and/or current in the secondary circuit and knowing the Volt
`age and/or current provided by the primary circuit, the pri
`mary controller can calculate the power transfer efficiency.
`By Sweeping a range of operating frequencies, noting the
`power transfer efficiency at each frequency, the operating
`frequency closest to resonance can be determined it corre
`sponds with the operating frequency that yields the best
`power transfer efficiency. In addition, the Voltage and current
`sensors 418, 422 can be used in conjunction with a protection
`algorithm in the secondary controller 428 to disconnect the
`load 424 if a fault condition is detected. This concept is
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`US 8,129,864 B2
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`7
`described in more detail in U.S. patent application Ser. No.
`1 1/855,710 entitled System and Method for Inductively
`Charging a Battery to Baarman et al., which was previously
`incorporated by reference.
`The secondary controller 428 may be essentially any type
`of microcontroller. In the illustrated embodiment, the second
`ary controller 428 is an ATTINY24V-10MU microcontroller.
`The secondary controller 428 generally includes an analog to
`digital converter, and is programmed to process the Voltage
`and/or current readings and transmit them to the primary
`controller 310 of the inductive power supply 300. The micro
`processor may also include other code unrelated to the fre
`quency or duty cycle control processes.
`Communication of the sensed Voltage and/or current in the
`secondary may be transmitted to the primary controller 310 in
`a variety of ways. In the illustrated embodiment, the informa
`tion may be transmitted using the signal resistor 432 or the
`wireless transmitter 430.
`In one embodiment, signal resistor 432 may be used to send
`information to the primary controller 310. The use of a signal
`resistor 432 to provide communication from the secondary to
`the primary was discussed in U.S. patent application Ser. No.
`1 1/855