US 7,825,537 B2
`(10) Patent No.:
`a2) United States Patent
`Freer
`(45) Date of Patent:
`Nov. 2, 2010
`
`
`US007825537B2
`
`(54)
`
`INDUCTIVE POWER TRANSFER SYSTEM
`AND METHOD
`
`5,831,841 A * 11/1998 Nishino oe 307/10.1
`6,301,128 BL
`10/2001 Janget al.
`6,421,600 BL*
`7/2002 Ross oo... eee eeeeeeeeeeeeeeee TOL/117
`6,489,745 Bl
`12/2002 Koreis
`:
`tne
`75
`6515878 Bl
`Inventor: Benjamin Freer, Rochester, NY (US)
`(75)
`2/2003 Meins et al.
`
`: 1/2004 Parketal.: A 6,683,438 B2
`
`
`
`(73) Assignee: Harris Corporation, Melbourne, FL
`6.912.137 B2
`6/2005 Bergheaper etal.
`(US)
`7,375,493 B2
`5/2008 Calhoonet al.
`
`(*) Notice:
`
`Subject to any disclaimer, the term ofthis
`ree iSpybyia,Fa unde 22
`~—
`y
`ys:
`(21) Appl. No.: 12/271,023
`(22)
`Filed:
`Nov. 14, 2008
`oo.
`,
`Prior Publication Data
`US 2010/0123451 Al
`May20, 2010
`
`(65)
`
`(51)
`
`Int. Cl.
`(2006.01)
`HO5K 1/02
`(2006.01)
`HOLF 21/04
`(2006.01)
`BoOL 9/00
`(52) US. Ch cececcccccccsceceeeeee 307/42; 336/115; 701/22
`(58) Field of Classification Search ..........0..0.... 701/22;
`180/2.1; 307/42; 191/10; 336/115, 116,
`336/123
`See application file for complete search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`* cited by examiner
`Primary Examiner—Shawn Riley
`(74) Attorney, Agent, or Firm—Fox Rothschild, LLP; Robert
`JSai
`ABSTRACT
`67)
`An inductive powertransfer system includes a base unit com-
`prising a first inductive elementfor providing input powerto
`a second inductive elementof a target unit providing output
`power, a positioning structure provided onat least one of the
`base unit and the target unit for removably positioning the
`second inductive element at a predetermined orientation and
`distancerelative to the first inductive element, a switch ele-
`ment configured for selectively applying a time varying elec-
`tric current to the first inductive element to produce a time
`varying magneticfield for inducing an electric current in the
`secondinductive element, and a controlcircuit for monitoring
`one parameter indicative of an efficiency of powertransfer
`and automatically selectively adjusting at least one charac-
`teristic of the time varying electric current responsive to the
`parameter to maximize an efficiency of powertransfer from
`the base unit to the target unit.
`
`5,396,538 A
`
`3/1995 Hongetal.
`
`28 Claims, 4 Drawing Sheets
`
`126
`
`122 —
`possre
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`103
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`102
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`U.S. Patent
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`Nov.2, 2010
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`Sheet 1 of 4
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`US 7,825,537 B2
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`COT =ET
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`Ex.1001
`APPLEINC./ Page 2 of 11
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`U.S. Patent
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`Nov.2, 2010
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`Sheet 2 of 4
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`US 7,825,537 B2
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`aNeer
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`Ex.1001
`APPLEINC./ Page 3 of 11
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`U.S. Patent
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`Nov.2, 2010
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`Sheet 3 of 4
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`US 7,825,537 B2
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`cor
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`Ex.1001
`APPLEINC./ Page 4 of 11
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`U.S. Patent
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`Nov.2, 2010
`
`Sheet 4 of 4
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`US 7,825,537 B2
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`(M) GIYNSASNVELL UIMOd
`
`FIG.4
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`POWERCONSUMED(W)
`
`(%) ADNSIDI44
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`Ex.1001
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`US 7,825,537 B2
`
`1
`INDUCTIVE POWER TRANSFER SYSTEM
`AND METHOD
`
`FIELD OF THE INVENTION
`
`The present inventionrelates to supplying electrical power
`wirelessly, and moreparticularly to systems and method for
`inductively supplying electrical power.
`
`BACKGROUND
`
`10
`
`Inductive powertransfer has been proposed as one method
`for wirelessly providing electrical power. In such a power
`transfer method, mutual
`inductance generally results in
`power being wirelessly transferred from a primary coil (or
`simply “primary”) in a power supply circuit to a secondary
`coil (or simply “secondary’”’) in a secondary circuit. Typically,
`the secondary circuit is electrically coupled with a device,
`such as a lamp, a motor, a battery charger or any other device
`poweredbyelectricity. The wireless connection provides a
`numberof advantages over conventional hardwired connec-
`tions. A wireless connection can reduce the chance of shock
`
`and can provide a relatively high level of electrical isolation
`between the power supply circuit and the secondary circuit.
`Inductive couplings can also makeit easier for a consumerto
`replace limited-life components. For example, in the context
`of lighting devices, an inductively powered lamp assembly
`can be easily replaced without the need to makedirect elec-
`trical connections. This not only makes the process easier to
`perform,butalso limits the risk of exposureto electric shock.
`In general, the use of inductive power has been limited to
`niche applications, such as for connections in wet environ-
`ments, due to power transfer efficiency concerns. Several
`methods have been proposed to improvethe efficiency of the
`inductive coupling, typically focused on the configuration of
`the primary and secondary coils. Such methods typically
`require not only close proximity of the primary andthe sec-
`ondary coils, but also careful tuning of the coil designs to
`match with one another to maximize the efficiency of the
`inductive coupling. This has placed significant limitations on
`the overall design and adaptability of inductively powered
`devices by increasing cost and complexity of conventional
`designs. Furthermore, even when such complex designs are
`used, the amount of powerthat can be transferred is further
`limited, reducing the amountofefficiency gains.
`
`SUMMARY
`
`Embodiments ofthe present invention provide systems and
`methodsfor inductively transferring power. For example, ina
`first embodimentof the present invention, a methodis pro-
`vided for inductively transferring power from a base unit
`providing input powerto a target unit providing output power,
`wherethe base unit andthe target unitare electrically isolated.
`The method can include positioning a second inductive ele-
`mentofthe target unit within a predetermined distance of a
`first inductive element of the base unit and applying a time
`varying electric current to thefirst inductive element to pro-
`duce a time varying magneticfield, the time varying magnetic
`field inducing an electric current in the second inductive
`element. The method can also include monitoringat least one
`parameter indicative of an efficiency of powertransfer from
`the base unit to the target unit and automatically adjusting at
`least one characteristic of the time varying electric current
`responsive to the parameter to maximize an efficiency of
`powertransfer from the base unitto the target unit.
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`2
`Ina second embodimentofthe present invention, an induc-
`tive power transfer system is provided. The system can
`include a base unitincludinga first inductive element config-
`ured for providing input powerto a second inductive element
`of a target unit providing output power, wherethe base unitis
`electrically isolated from the target unit. The system can also
`include a positioning structure providedonat least one of the
`base unit and the target unit for removably positioning the
`second inductive element at a predetermined orientation and
`distance relativeto the first inductive element. The system can
`further include a switch element for selectively applying a
`time varying electric currentto the first inductive elementto
`producea time varying magneticfield, the time varying mag-
`netic field inducing anelectric current in the second inductive
`element. The system can also include a control circuit con-
`figured for monitoring at least one parameterindicative of an
`efficiency of power transfer from the base unit to the target
`unit and for automatically adjusting at least one characteristic
`of the time varying electric current responsive to the param-
`eter to maximizean efficiency ofpowertransfer from the base
`unit to the target unit.
`Ina third embodimentof the present invention, A DC-DC
`converter is provided. The converter can include a input cir-
`cuit for receiving a DC input voltage and an output circuit
`electrically coupled to the input circuit. The output circuit can
`comprise a load sub-circuit electrically coupled to a converter
`sub-circuit includingatleast a first inductive element and at
`least one switch element having a switch control node respon-
`sive to a first control voltage for selectively alternating the
`switch element between an openstate anda closed state. The
`convertor can also include a control circuit having an input
`nodeelectrically coupled to anode within the load sub-circuit
`and an output nodeelectrically coupled to the switch control
`node, the control circuit generating at the output nodea peri-
`odic voltage signal adjustable to one or more operating fre-
`quencies based on a difference between a second control
`voltage at the input node and a reference voltage. In the
`converter, an inductance and a physical arrangementof the
`first inductive elementis selected for the first inductive ele-
`ment to generate a permeating magnetic field that at least
`partially permeates a second inductive element electrically
`isolated from thefirst inductive element, where the permeat-
`ing magneticfield inducesa substantially self-resonantoscil-
`lation in the second inductive elementfor at least one of the
`operating frequencies. Furthermore, the control circuit is fur-
`ther configured to adjust the periodic voltage signal to adjust
`an internal voltage level at the internal node to minimize the
`difference.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a block diagram of a DC-DC convertercircuit
`in accordance with an embodimentof the present invention.
`FIG. 2 shows a schematic of a DC-DC convertercircuit in
`
`FIG.1 using a buck converter topology in the base unit anda
`full-waverrectifier circuit in the target unit.
`FIG. 3A shows the base unit of the inductive DC-DC
`
`converter circuit in FIG. 1 arranged according to a boost
`convertor topology.
`FIG. 3B showsthe base unit of the inductive DC-DC con-
`
`verter circuit in FIG. 1 arranged according to a buck-boost
`convertor topology.
`FIG.4 is a plot showing powerefficiency and powertrans-
`ferred as a function of input power consumedfor an inductive
`DC-DCconverter circuit having a buck converter topology in
`accordance with an embodimentofthe present invention.
`
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`3
`DETAILED DESCRIPTION
`
`US 7,825,537 B2
`
`4
`rectifying element 122 for the time-varying signal generated
`by the second inductive element 120 in response to coupling
`with thefirst inductive element 112. This generated DC volt-
`age signal can then be applied across a second load 126 with
`an impedance 72 in the target unit 103 to produce an output
`DC voltage Vout2.
`One of ordinary skill in the art will recognize that the
`amount of powertransferred from the base unit 102 to the
`target unit 103 is dependent on the amount of magnetic cou-
`pling betweenthe first inductive element 112 and the second
`inductive element 120. In conventional designs, the amount
`of magnetic coupling is adjusted by matching the inductor
`coil design of the inductive elements 112, 120. However, this
`typically results in a base unit design compatible with only a
`particular target unit design, limiting the flexibility ofthe base
`unit to power additional target units. Furthermore, because a
`high degree of inductor coil matching is generally required,
`the operational margin for such base unit/target unit combi-
`nations is also limited.
`
`the second inductive element 120, as in conventional designs,
`the switching network 114 is used to adjust the operating
`frequency of the existing first inductive element 112. The
`operating frequency can then be adjusted until the self-reso-
`nant oscillation is induced in the second inductive element
`
`The present invention is described with reference to the
`attached figures, wherein like reference numerals are used
`throughoutthe figures to designate similar or equivalent ele-
`ments. The figures are not drawn to scale and they are pro-
`vided merely to illustrate the instant
`invention. Several
`aspects ofthe invention are described below with reference to
`example applicationsfor illustration. It should be understood
`that numerousspecific details, relationships, and methods are
`set forth to provide a full understanding of the invention. One
`having ordinary skill in the relevant art, however, will readily
`recognize that the invention can be practiced without one or
`more of the specific details or with other methods. In other
`instances, well-knownstructures or operations are not shown
`in detail to avoid obscuring the invention. The present inven-
`tion is notlimited by the illustrated ordering of acts or events,
`as some acts may occur in different orders and/or concur-
`rently with other acts or events. Furthermore, not all illus-
`An alternate method of efficiently transferring power
`trated acts or events are required to implement a methodology
`betweenthe base unit 102 and the target unit 103 is to provide
`in accordance with the present invention.
`operating conditionsthat result in a resistance of the primary
`A block diagram of an inductive DC-DC converter circuit
`coil to falls to approximately zero and an impedance of the
`100 for inductive power transfer in accordance with an
`secondary coil becoming increasingly resistive. This causes
`embodimentofthe present invention is shown in FIG. 1. The
`the input resistance of the primary coil to also become
`circuit 100 can include a base unit 102 providing input power
`increasingly resistive and the amount of powertransferred
`and a target unit 103 providing output power, where the base
`between the primary and secondary coils is also increased, as
`unit 102 and the target unit 103 are electrically isolated. The
`in a conventional powertransfer, enhancing powertransfer
`target unit 103 can be electrically coupled to one or more
`efficiency. This phenomena occurs when a least a portion of
`electronic devices to provide power. By way of example, and
`the time-varying magnetic field generated by a primary coil
`not by wayoflimitation, these devices can includebatteries,
`operated at one or more switching frequencies permeates the
`display units, keypads, and the like. The base unit 102 can
`include a DC voltage supply 104 for providing an input DC
`secondary coil and induces an oscillation in the secondary
`
`voltage (Vin). The base unit 102 can includeaload 106 having coil at its self resonant frequency,i.e., a self-resonant oscil-
`an impedance 71 having at least one internal node 108. In
`lation. Accordingly,
`in the various embodiments of the
`some embodiments, the load 106 can also be used to provide
`present invention, rather than attempting to precisely match
`the coil characteristics of the first inductive element 112 and
`a wired output voltage Vout1. However, the invention is not
`limited in this regard and the load 106 can provide multiple
`output voltages.
`As shown in FIG.1, the DC voltage supply 104 andthe load
`106 are electrically coupled via a converter sub-circuit 110.
`The converter sub-circuit 110 includes an first inductive ele-
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`ment 112 anda switching network 114for directing current to
`or from the first inductive element 112 at an operating fre-
`quency. In FIG. 1, first inductive element 112 comprises an
`inductor L1. The switching network 114 can include an input
`node N2 for receiving a periodic voltage signal Vctrl for
`adjusting an operating frequency of the converter sub-circuit
`based on a voltage at node 108. The input node 116 andthe
`internal node 108 can be electrically coupled via a controller
`element (CTRL) 118. The CTRL 118 can be configured to
`monitor the voltage Vnode at node 108 andto adjust Vetrl at
`node 116. Vetrl can be adjusted by CTRL 118 responsive to
`comparing Vnode to a reference voltage Vref. In some
`embodiments, as shown in FIG. 1, Vref can be provided to
`CTRL 118. In other embodiments, Vref can be internally
`generated. Details of the operation of the converter sub-cir-
`cuit 110 and CTRL 118 will be described in further detail
`
`below with respect to FIGS. 2, 3A, and 3B.
`In operation for inductive powertransfer, the first inductive
`element 112 is utilized as the primary coil inthe base unit 102
`for transferring powerto the target unit 103. In particular, the
`powercan betransferred to the target unit 103 via a secondary
`coil formed from a second inductive element 120 in the target
`unit 103. As shown in FIG. 1, the secondary coil can be a
`second inductor L2. The secondinductive element 120 can be
`electrically coupledto a rectifying element 122 for generating
`a DC voltage signal between node 124 and node 125 of the
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`120. The operating frequency for the base unit for inducing
`the self-resonant oscillation in the second inductive element
`
`can vary depending on the separation betweenthefirst induc-
`tive element 112 and the second inductive element 120, as the
`separation affects the magnetic field inducing an oscillation
`in the second inductive element 120. Additionally, the oper-
`ating frequency for the base unit can also vary depending on
`the configuration ofthe rectifying element 122 and the second
`load 126.
`
`in the various embodiments of the present
`Therefore,
`invention, a first inductive element 112 configuration can be
`selected such that, for at least at one operating frequency,
`magnetic coupling to the second inductive element 120 at a
`pre-determined distance occurs that transfers power propor-
`tionalto a simple voltage divider ofthe load 106 and the input
`resistance ofthefirst inductive element 112. Although induc-
`ing a self resonant oscillation provides the most efficient
`powertransfer, the invention is not limited in this regard. In
`the some embodiments ofthe present invention, the inductive
`DC-DCconverter 100 can be configured operate in proximity
`to the self-resonant frequency, albeit at a reducedefficiency.
`Thatis, if the oscillation at the second inductive element 120
`does not occurat its self-resonant frequency, the input resis-
`tance of the primary coil (the first inductive element 112)is
`decreased. As a result, the amount ofpowertransferred is also
`decreased, decreasing powertransfer efficiency.
`
`Ex.1001
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`US 7,825,537 B2
`
`5
`Althoughthefirst inductive element 112 can be paired with
`any type of switching network to adjust an operating fre-
`quency, a converter sub-circuit comprising a DC-DC switch-
`ing mode powersupply circuit (SMC circuit) can be used to
`provide both thefirst inductive element 112 and the switching
`network 114. SMC circuits are designed to convert one DC
`voltage to anotherby storing energy in a magnetic component
`(typically an inductoror a transformer) fora period oftime. In
`operation, adjustment of the duty cycle (the ratio of on/off
`time) of a switching element within the SMC circuit adjusts
`the amount of powertransferred to a load in the SMCcircuit.
`More importantly, by adjusting the duty cycle, the operating
`frequency of the magnetic component(the inductor) in SMC
`circuit can also be adjusted. Accordingly, one aspect of
`present invention provides for using an SMCcircuit to pro-
`vide the converter sub-circuit 110.
`
`In order to provide operation of the second inductive ele-
`ment 120 atits self resonant frequency, the CTRL 118 can be
`configured to indirectly monitor the amount of powertrans-
`ferred to the second inductive element 120 by monitoring the
`voltage generated across at least a portion of the load 106.
`That is, as the frequency ofoscillation in the second inductive
`element 120 approachesits self-resonant frequency,the input
`impedanceofthe first inductive element 112 becomes sub-
`stantially moreresistive and the amount of powertransferred
`to the target unit 103 increases. Consequently, the voltage
`dropped across other portions of the base unit, including the
`load 106, approaches the values expected for a substantially
`resistive input impedancefor the first inductive element 112.
`Accordingly, by configuring the CTRL 118 to monitor the
`voltage level at a node of the load 106, such as Vnode at node
`108, the CTRL 118 can adjust the duty cycle for the SMC
`circuit to cause a particular voltage level at node 108. There-
`fore, the amount ofpower the amount of powertransferred to
`the targetunit 103 is effectively controlled and maximized.In
`some configurations of the inductive DC-DC converter 200,
`minimizing the voltage value Vnodeat node 108 can result in
`a self-resonant oscillation in the second inductive element.
`
`However, in other configurations of the inductive DC-DC
`converter 200, even after such minimizing of Vnode, the
`second inductive element 120 maystill not oscillate at its
`self-resonant frequency. For example, if processing varia-
`tions result in variations in the first and second inductive
`
`elements 112, 120 (or any other elements), the self-resonant
`frequency expected for the second inductive element 120 can
`vary and a different voltage value for Vnode can be needed to
`maximize power transfer. Accordingly, in such cases, the
`powertransfer still occur, albeit at a lowerefficiency, until a
`new voltage value forVnodeis selected. Aninductive DC-DC
`converter using an SMCcircuit is conceptually illustrated
`with respect to FIG.2.
`FIG. 2 shows a schematic of an inductive DC-DC converter
`circuit 200 including an SMCcircuit, in particular a buck
`convertor topology. In FIG.2, the circuit 200 includes a base
`unit 102 and a target unit 103, as previously described with
`respect to FIG. 1. However, in FIG. 2, the first inductive
`element 112 and the switching network 114 are configured as
`an SMC circuit having a buck converter topology. A switch
`element 202, a rectifying element 204, andthefirst inductive
`element 112 are arranged such that when switch element 202
`is closed, the currentpath in circuit 200 follows a loop formed
`by the DC voltage supply 104, the first inductive element 112,
`and the load 106. When the switch element 202 is open, the
`current path in circuit 200 follows a loop formed by the
`rectifier element 204, the first inductive element 112, and the
`load 106. Accordingly, first inductive element 112, rectifier
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`element 204, and switching element 202 can bereferred to
`collectively as an SMC sub-circuit 112, 204, 202.
`In some embodiments of the present invention, the switch
`element 202 comprises a single switch S1 having a control
`node N2 that respondsin a control signal. The single switch
`S1 can comprise any type of electrically controlled switch,
`including, but not limited to, bipolar junction (BJT)transis-
`tors and field effect (FET) transistors. In such devices, the
`control node N2 can comprise the base of the BJT or the gate
`of the FET transistor. As shown in FIG. 2, the rectifying
`element 204 can comprise a diode D1. However,the invention
`is not limited in this regard. In some embodiments, the recti-
`fying element 204 can also comprise any type of synchro-
`nouslyelectrically controlled switch, including, but not lim-
`ited to, bipolar junction (BJT) transistors and field effect
`(FET) transistors. That is, a switch that closes when switch $1
`is open and vice versa. In such embodiments, the control
`signal for the rectifying element 204 can be a complementor
`inverse of the control signal being provided to the switch
`element 202.
`As shownin FIG.2, the load 106 includes resistors RIA
`and R1B and capacitor C1. However, the invention is not
`limited to solely this configuration for the load 106 and any
`combination of resistors, capacitors, and inductors can be
`used to form the load 106. In FIG. 2, node 108 is the common
`node between resistors R1A and R1B. Additionally, as pre-
`viously described, the load 106 can be used to provide an
`output voltage Vout1.
`As previously described, the target unit 103 includes a
`second inductive element 120, a rectifier circuit 122, and a
`load 126. As shown in FIG.2, the rectifier element 122 can
`include diodes D1-D4in a full-waverectification configura-
`tion for generating a DC voltage signal from the time-varying
`signal generated by the second inductive element 120. How-
`ever, the invention is not limited in this regard. I’or example,
`any arrangement of components suitable for half-waverecti-
`fication or full-waverectification can be used with the various
`embodimentsofthe present invention. Also as shown in FIG.
`2, the load 126 in the target unit 103 includes a capacitor C2
`and a resistor R2. However, the inventionis not limited in this
`regard and any combination of resistors, capacitors, and/or
`inductors can be used in load 126.
`
`to improve magnetic coupling
`In some embodiments,
`between the first and second inductive elements 112, 120, a
`capacitor network 206 can be usedto electrically couple the
`secondinductive element 120 to the rectifier circuit 122. Such
`a capacitive network 206 can include one or more capacitors
`(C3) in parallel with the second inductive element 120. The
`capacitive can also include one or more capacitors (C4, C5) to
`electrically couple the second inductive element 120 to the
`rectifier circuit 122. The capacitive network 206 can be used
`to reduce the imaginary componentin thetarget unit 103, thus
`presenting a moreresistive load withoutaltering the operating
`frequency in the base unit 102 required for inducing a self-
`resonant oscillation in the second inductive element 120.
`In operation, circuit 200 provides an output voltage Vout2
`as follows. First, the base unit 102 andthe target unit 103 are
`placed andaligned in relative proximity to each other. Since
`the fields lines ofthe magnetic field generated by the base unit
`will have a particular direction, the second inductive element
`120 can be positioned in the path of the field lines of the
`generated magnetic field. For example in the case of hand-
`wired air coil inductors having inductances between 100 nH
`and 500 nH andan utilizing operating frequency of 1-4 MHz,
`the first and second inductive elements can to be positioned
`within a distance of 10-15 cm or less to maximize power
`transfer. This distance, however, can vary depending on the
`
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`US 7,825,537 B2
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`7
`amount of powerbeing transferred, the operating frequency,
`and the inductancesof the inductor coils. Furthermore, in the
`case of inductor coils, the coil axis of each of the inductor
`coils can be placed along a commonparallel! direction. That
`is, an arrangementcan be selected suchthat the dot product of
`the directional vector for an axis of each ofthe inductorcoils
`is chosen to be one or approximately one. However, precise
`alignmentis not required in the various embodiments of the
`present invention and the directional vectors need only be
`substantially parallel. For example, the Present Inventors
`have found that the alignment variation to cause a 10%
`decrease in powertransfer efficiency is >25 degrees. In some
`embodimentsofthe present invention, a positioning structure
`(s) 115, such as contacting or interlocking protrusions or
`edges can be provided on a support and/or housingofthe base
`unit 102 and/or the target unit 103 to facilitate alignment.
`Although exemplary types of inductorcoils, are described
`above,the invention is not limited in this regard. For example,
`any type ofdiscrete inductorcoils, including butnotlimited to
`cylindrical inductorcoils, single or multilayer inductor coils,
`wire spiral inductor coils, and toroidal inductor coils can be
`used in the various embodiments of the present invention.
`Furthermore, integrated inductor coils, such as printed circuit
`board (PCB) micro-strip spiral coils or spiral coils formed on
`an integrated circuit (IC) can also be used with the various
`embodiments of the present
`invention. Additionally,
`the
`inductance values and operating frequencies presented above
`are forillustrative purposes only. For example, in some other
`embodiments, the inductances values can be 1-100 uH and
`the corresponding operating frequencies can be 400-500
`MHz. However, the present invention is not limited in this
`regard. Any combination of operating frequencies and induc-
`tance values can be used in the various embodiments of the
`
`present invention.
`After the first and second inductive elements 112, 120 are
`positioned and aligned, an input voltage Vin can be provided
`by the DC input supply 104 and a control signal can provided
`at node 116 of the switching element 202 (andrectifier ele-
`ment 204, if applicable) by CTRL 118 based on the voltage
`Vnode at node N1. As previously described, CTRL 118 is
`configured to provide a periodic voltage signal, where the
`frequency of the periodic voltage signal Vctrl specifies the
`duty cycle for the switching element 202. Although the buck
`converter topology shown in FIG. 2 is typically operated
`using a square wavesignal, the inventionis notlimited in this
`regard. Other types ofperiodic voltage signals, including, but
`not limited to sinusoidal, triangular, or sawtooth waveforms
`can also be generated by CTRL 118.
`Asa result of the periodic voltage signal Vetrl, the CTRL
`118 causes the switching element 202 to open andclose at a
`frequency ofVctrl. Consequently, the base unit 102 alternates
`between the two current paths described above. Asa result of
`these alternating current paths, the first inductive element 112
`continually charges and discharges. However, one ofordinary
`skill in the art will recognize that the buck convertor topology
`provides a steady state voltage output voltage Voutl across
`load 106. Furthermore, as a constant voltage results across
`load 106, a steady-state output voltage Vnode also develops at
`node 108.
`
`As noted above, the voltage dropped across the load 106
`can be predicted when the secondinductive element 120is at
`its self-resonant frequency. Consequently, the voltage at an
`inner node of the load 106 (Vctrl) can also be predicted.
`Therefore, by utilizing Vrefas a setpoint for Vetrl, CTRL 118
`can adjustthe duty cycle of for the SMC sub-circuit 112, 202,
`204, which adjusts the operating frequency ofthefirst induc-
`tive element 112 and thus the amount of powertransferred to
`
`8
`the target unit 103. Accordingly, as conditions vary, whether
`due to changes in the placementofthe base unit 102 relative
`to the target unit 103 or due to changes in the characteristics
`of components in the base unit 102 or the target unit 103, the
`CTRL 118 can compare Vnode to Vref and compensate Vctrl
`appropriately. For example, if the CTRL 118 detects a differ-
`ence between Vnodeand Vref, the duty cycle can be adjusted
`until the difference is minimized.
`Therefore,
`in the various embodiments of the present
`invention, the CTRL 118 caninclude logic for determining a
`value ofVctrl from Vnode and Vref values. In one exemplary
`embodiment, the logic can comprise logic for accessing a
`lookup table for adjusting Vctrl.
`In another exemplary
`embodiment, the logic can comprise logic that adjusts Vctrl
`based on an actual difference between Vctrl and Vref, a mag-
`nitude of this actual difference, or both. These exemplary
`embodimentsare provided by way of example and not by way
`of limitation. One of ordinary skill in the art will readily
`recognize that various methodsand devices for implementing
`CTRL 118 are available. For example, a power supply can
`include a circuit for automatically adjusting the frequency of
`operation for the pulse width modulation being used by
`implementing an error amplifier for obtaining a value for
`Vctrl based on Vref and Vnode.
`
`The present invention is not limited to a buck converter
`topology. In other embodiments ofthe invention,the arrange-
`ment of the first inductive element 112, the switch element
`202, and the rectifying element 204 in the base unit can be
`changed to provide alternative topologies for the SMC sub-
`circuit 112, 202, 204 in FIG.2. For example, in some embodi-
`ments, a boost converter topology or an buck-boostorinvert-
`ing converter topology can be used.
`FIG. 3A showsa first alternate base unit 300 for the circuit
`
`5
`
`10
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`15
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`20
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`25
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`30
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`35
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`in FIG. 2 havinga first alternate topologyfor the SMC sub-
`circuit in PIG. 2 in accordance with another embodiment of
`
`the present invention. As shownin FIG. 3.A, the arrangement
`ofthefirst inductive element 112, the switching element 202,
`and therectifying element 204 in the base unit 300 provides a
`boost converter topology. That is the switch element 202, the
`rectifying element 204, and thefirst inductive element 112 are
`arranged such that when switch element 202 is closed, the
`current path in base unit 300 follows a loop comprising the
`DC voltage supply 104, the first inductive element 112, and
`the closed switching element 202. When the switching ele-
`ment 202 is open,the current path in the base unit 300 follows
`a loop comprising the DC voltage supply 104, thefirst induc-
`tive element 112, the rectifier element 204, and the load 106.
`FIG. 3B shows a second alternate base unit 350 for the