(12) United States Patent
`Freer
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7825,537 B2
`Nov. 2, 2010
`
`US00782.5537B2
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`(54) INDUCTIVE POWER TRANSFER SYSTEM
`AND METHOD
`
`(*) Notice:
`
`75
`(75) Inventor: Benjamin Freer, Rochester, NY (US)
`(73) Assignee: Harris Corporation, Melbourne, FL
`(US)
`Subject to any disclaimer, the term of this
`past llists .listed under 35
`M
`YW-
`y
`yS.
`(21) Appl. No.: 12/271,023
`(22) Filed:
`Nov. 14, 2008
`O
`O
`Prior Publication Data
`US 2010/O123451A1
`May 20, 2010
`
`(65)
`
`(51) Int. Cl.
`(2006.01)
`H05K L/02
`(2006.01)
`HOIF 2/04
`(2006.01)
`B60L 9/00
`(52) U.S. Cl. ............................ 307/42: 336/115; 701/22
`(58) Field of Classification Search ................... 701/22,
`180/2.1; 307/42; 191/10; 336/115, 116,
`336/123
`See application file for complete search history.
`References Cited
`U.S. PATENT DOCUMENTS
`
`(56)
`
`5,831,841 A * 1 1/1998 Nishino ..................... 307/10.1
`6,301,128 B1
`10/2001 Jang et al.
`6.421,600 B1
`7/2002 Ross .......................... 701 117
`6,489,745 B1
`12/2002 Koreis
`6,515,878 B1
`2/2003 Meins et al.
`6,683.438 B2
`1/2004 Park et al.
`6,912,137 B2
`6/2005 Ber et al.
`7,375,493 B2
`5/2008 Calhoon et al.
`* cited by examiner
`Primary Examiner Shawn Riley
`(74) Attorney, Agent, or Firm—Fox Rothschild, LLP; Robert
`J. Sacco
`ABSTRACT
`(57)
`An inductive power transfer system includes a base unit com
`prising a first inductive element for providing input power to
`a second inductive element of a target unit providing output
`power, a positioning structure provided on at least one of the
`base unit and the target unit for removably positioning the
`second inductive element at a predetermined orientation and
`distance relative 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 magnetic field for inducing an electric current in the
`second inductive element, and a control circuit for monitoring
`one parameter indicative of an efficiency of power transfer
`and automatically selectively adjusting at least one charac
`teristic of the time varying electric current responsive to the
`parameter to maximize an efficiency of power transfer from
`the base unit to the target unit.
`
`5,396,538 A
`
`3/1995 Hong et al.
`
`28 Claims, 4 Drawing Sheets
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`GOOGLE AND SAMSUNG EXHIBIT 1001, 0001
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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 7825,537 B2
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`GOOGLE AND SAMSUNG EXHIBIT 1001, 0002
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`U.S. Patent
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`US 7825,537 B2
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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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`U.S. Patent
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`Nov. 2, 2010
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`Sheet 4 of 4
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`US 7825,537 B2
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`(NA) C3d-3-SNwed LINAOd
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`GOOGLE AND SAMSUNG EXHIBIT 1001, 0005
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`US 7,825,537 B2
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`1.
`INDUCTIVE POWER TRANSFER SYSTEM
`AND METHOD
`
`FIELD OF THE INVENTION
`
`The present invention relates to supplying electrical power
`wirelessly, and more particularly to systems and method for
`inductively supplying electrical power.
`
`BACKGROUND
`
`2
`In a second embodiment of the present invention, an induc
`tive power transfer system is provided. The system can
`include a base unit including a first inductive element config
`ured for providing input power to a second inductive element
`of a target unit providing output power, where the base unit is
`electrically isolated from the target unit. The system can also
`include a positioning structure provided on at least one of the
`base unit and the target unit for removably positioning the
`second inductive element at a predetermined orientation and
`distance relative to the first inductive element. The system can
`further include a switch element for selectively applying a
`time varying electric current to the first inductive element to
`produce a time varying magnetic field, the time varying mag
`netic field inducing an electric current in the second inductive
`element. The system can also include a control circuit con
`figured for monitoring at least one parameter indicative 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 maximize an efficiency of power transfer from the base
`unit to the target unit.
`In a third embodiment of 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 including at least 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 open state and a closed state. The
`convertor can also include a control circuit having an input
`node electrically coupled to a node within the load sub-circuit
`and an output node electrically coupled to the Switch control
`node, the control circuit generating at the output node a 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 arrangement of the
`first inductive element is 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 the first inductive element, where the permeat
`ing magnetic field induces a Substantially self-resonant oscil
`lation in the second inductive element for 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.
`
`Inductive power transfer 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
`powered by electricity. The wireless connection provides a
`number of 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 make it easier for a consumer to
`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 make direct elec
`trical connections. This not only makes the process easier to
`perform, but also limits the risk of exposure to 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 improve the 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 and the 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 power that can be transferred is further
`limited, reducing the amount of efficiency gains.
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`SUMMARY
`
`Embodiments of the present invention provide systems and
`methods for inductively transferring power. For example, in a
`first embodiment of the present invention, a method is pro
`vided for inductively transferring power from a base unit
`providing input power to a target unit providing output power,
`where the base unit and the target unit are electrically isolated.
`The method can include positioning a second inductive ele
`ment of the target unit within a predetermined distance of a
`first inductive element of the base unit and applying a time
`varying electric current to the first inductive element to pro
`duce a time varying magnetic field, the time varying magnetic
`field inducing an electric current in the second inductive
`element. The method can also include monitoring at least one
`parameter indicative of an efficiency of power transfer 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
`power transfer from the base unit to the target unit.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a block diagram of a DC-DC converter circuit
`in accordance with an embodiment of the present invention.
`FIG. 2 shows a schematic of a DC-DC converter circuit in
`FIG. 1 using a buck converter topology in the base unit and a
`full-waver rectifier 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 shows the 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 power efficiency and power trans
`ferred as a function of input power consumed for an inductive
`DC-DC converter circuit having a buck converter topology in
`accordance with an embodiment of the present invention.
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`DETAILED DESCRIPTION
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`US 7,825,537 B2
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`rectifying element 122 for the time-varying signal generated
`by the second inductive element 120 in response to coupling
`with the first inductive element 112. This generated DC volt
`age signal can then be applied across a second load 126 with
`an impedance Z2 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 power transferred from the base unit 102 to the
`target unit 103 is dependent on the amount of magnetic cou
`pling between the 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 of the 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.
`An alternate method of efficiently transferring power
`between the base unit 102 and the target unit 103 is to provide
`operating conditions that result in a resistance of the primary
`coil to falls to approximately Zero and an impedance of the
`secondary coil becoming increasingly resistive. This causes
`the input resistance of the primary coil to also become
`increasingly resistive and the amount of power transferred
`between the primary and secondary coils is also increased, as
`in a conventional power transfer, enhancing power transfer
`efficiency. This phenomena occurs when a least a portion of
`the time-varying magnetic field generated by a primary coil
`operated at one or more Switching frequencies permeates the
`secondary coil and induces an oscillation in the secondary
`coil at its self resonant frequency, i.e., a self-resonant oscil
`lation. Accordingly, in the various embodiments of the
`present invention, rather than attempting to precisely match
`the coil characteristics of the first inductive element 112 and
`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
`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 between the first 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 of the rectifying element 122 and the second
`load 126.
`Therefore, in the various embodiments of the present
`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
`tional to a simple voltage divider of the load 106 and the input
`resistance of the first inductive element 112. Although induc
`ing a self resonant oscillation provides the most efficient
`power transfer, the invention is not limited in this regard. In
`the some embodiments of the present invention, the inductive
`DC-DC converter 100 can be configured operate in proximity
`to the self-resonant frequency, albeit at a reduced efficiency.
`That is, 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 of power transferred is also
`decreased, decreasing power transfer efficiency.
`
`The present invention is described with reference to the
`attached figures, wherein like reference numerals are used
`throughout the 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 of the invention are described below with reference to
`example applications for illustration. It should be understood
`that numerous specific 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-known structures or operations are not shown
`in detail to avoid obscuring the invention. The present inven
`tion is not limited 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
`trated acts or events are required to implement a methodology
`in accordance with the present invention.
`A block diagram of an inductive DC-DC converter circuit
`100 for inductive power transfer in accordance with an
`embodiment of the present invention is shown in FIG.1. The
`circuit 100 can include a base unit 102 providing input power
`and a target unit 103 providing output power, where the base
`unit 102 and the target unit 103 are electrically isolated. The
`target unit 103 can be electrically coupled to one or more
`electronic devices to provide power. By way of example, and
`not by way of limitation, these devices can include batteries,
`display units, keypads, and the like. The base unit 102 can
`include a DC voltage supply 104 for providing an input DC
`voltage (Vin). The base unit 102 can include a load 106 having
`an impedance Z1 having at least one internal node 108. In
`some embodiments, the load 106 can also be used to provide
`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 and the load
`106 are electrically coupled via a converter sub-circuit 110.
`The converter sub-circuit 110 includes an first inductive ele
`ment 112 and a switching network 114 for 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 and the
`internal node 108 can be electrically coupled via a controller
`element (CTRL) 118. The CTRL 118 can be configured to
`monitor the voltage V node at node 108 and to adjust Vctrl at
`node 116. Vctrl can be adjusted by CTRL 118 responsive to
`comparing Vinode 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 power transfer, the first inductive
`element 112 is utilized as the primary coil in the base unit 102
`for transferring power to the target unit 103. In particular, the
`power can be transferred 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 second inductive element 120 can be
`electrically coupled to a rectifying element 122 for generating
`a DC voltage signal between node 124 and node 125 of the
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`Although the first 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 power supply circuit (SMC circuit) can be used to
`provide both the first inductive element 112 and the switching
`network 114. SMC circuits are designed to convert one DC
`Voltage to another by storing energy in a magnetic component
`(typically an inductor or a transformer) for a period of time. 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 power transferred to a load in the SMC circuit.
`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
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`present invention provides for using an SMC circuit to pro
`vide the converter sub-circuit 110.
`In order to provide operation of the second inductive ele
`ment 120 at its self resonant frequency, the CTRL 118 can be
`configured to indirectly monitor the amount of power trans
`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 of oscillation in the second inductive
`element 120 approaches its self-resonant frequency, the input
`impedance of the first inductive element 112 becomes sub
`stantially more resistive and the amount of power transferred
`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 impedance for 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 Vinode 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 of power the amount of power transferred to
`the target unit 103 is effectively controlled and maximized. In
`some configurations of the inductive DC-DC converter 200,
`minimizing the voltage value Vinode at node 108 can result in
`a self-resonant oscillation in the second inductive element.
`However, in other configurations of the inductive DC-DC
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`converter 200, even after such minimizing of Vinode, the
`second inductive element 120 may still 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 Vinode can be needed to
`maximize power transfer. Accordingly, in Such cases, the
`power transfer still occur, albeit at a lower efficiency, until a
`new voltage value for Vinode is selected. An inductive DC-DC
`converter using an SMC circuit is conceptually illustrated
`with respect to FIG. 2.
`FIG.2 shows a schematic of an inductive DC-DC converter
`circuit 200 including an SMC circuit, 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, and the first inductive
`element 112 are arranged such that when switch element 202
`is closed, the current path 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 be referred 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 responds in 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
`nously electrically 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 S1
`is open and vice versa. In such embodiments, the control
`signal for the rectifying element 204 can be a complement or
`inverse of the control signal being provided to the switch
`element 202.
`As shown in FIG. 2, the load 106 includes resistors R1A
`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-D4 in a full-wave rectification 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. For example,
`any arrangement of components suitable for half-wave recti
`fication or full-wave rectification can be used with the various
`embodiments of the 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 invention is not limited in this
`regard and any combination of resistors, capacitors, and/or
`inductors can be used in load 126.
`In some embodiments, to improve magnetic coupling
`between the first and second inductive elements 112, 120, a
`capacitor network 206 can be used to electrically couple the
`second inductive element 120 to the rectifiercircuit 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 component in the target unit 103, thus
`presenting a more resistive load without altering 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 and the target unit 103 are
`placed and aligned in relative proximity to each other. Since
`the fields lines of the 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 and an utilizing operating frequency of 1-4MHz,
`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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`amount of power being transferred, the operating frequency,
`and the inductances of the inductor coils. Furthermore, in the
`case of inductor coils, the coil axis of each of the inductor
`coils can be placed along a common parallel direction. That
`is, an arrangement can be selected Such that the dot product of
`the directional vector for an axis of each of the inductor coils
`is chosen to be one or approximately one. However, precise
`alignment is 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 power transfer efficiency is >25 degrees. In some
`embodiments of the present invention, a positioning structure
`(s) 115. Such as contacting or interlocking protrusions or
`edges can be provided on a Support and/or housing of the base
`unit 102 and/or the target unit 103 to facilitate alignment.
`Although exemplary types of inductor coils, are described
`above, the invention is not limited in this regard. For example,
`any type of discrete inductor coils, including but not limited to
`cylindrical inductor coils, 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 for illustrative purposes only. For example, in some other
`embodiments, the inductances values can be 1-100 uFH 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 (and rectifier ele
`ment 204, if applicable) by CTRL 118 based on the voltage
`Vinode 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 wave signal, the invention is not limited in this
`regard. Other types of periodic Voltage signals, including, but
`not limited to sinusoidal, triangular, or sawtooth waveforms
`can also be generated by CTRL 118.
`As a result of the periodic voltage signal Vctrl, the CTRL
`118 causes the switching element 202 to open and close at a
`50
`frequency of Vctrl. Consequently, the base unit 102 alternates
`between the two current paths described above. As a result of
`these alternating current paths, the first inductive element 112
`continually charges and discharges. However, one of ordinary
`skill in the art will recognize that the buck convertor topology
`provides a steady State Voltage output Voltage Vout1 across
`load 106. Furthermore, as a constant Voltage results across
`load 106, a steady-state output voltage V node also develops at
`node 108.
`As noted above, the voltage dropped across the load 106
`can be predicted when the second inductive element 120 is 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 V.ctrl, CTRL 118
`can adjust the duty cycle of for the SMC sub-circuit 112, 202,
`204, which adjusts the operating frequency of the first induc
`tive element 112 and thus the amount of power transferred to
`
`30
`
`8
`the target unit 103. Accordingly, as conditions vary, whether
`due to changes in the placement of the 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 Vinode to Vref and compensate Vctrl
`appropriately. For example, if the CTRL 118 detects a differ
`ence between Vinode and Vref, the duty cycle can be adjusted
`until the difference is minimized.
`Therefore, in the various embodiments of the present
`invention, the CTRL 118 can include logic for determining a
`value of Vctrl from Vinode 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
`embodiments are provided by way of example and not by way
`of limitation. One of ordinary skill in the art will readily
`recognize that various methods and 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 Vinode.
`The present invention is not limited to a buck converter
`topology. In other embodiments of the 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 oran buck-boost or invert
`ing converter topology can be used.
`FIG.3A shows a first alternate base unit 300 for the circuit
`in FIG. 2 having a first alternate topology for the SMC sub
`circuit in FIG. 2 in accordance with another embodiment of
`the present invention. As shown in FIG. 3A, the arrangement
`of the first inductive element 112, the switching element 202,
`and the rectifying element 204 in the base unit 300 provides a
`boost converter topology. That is the switch element 202, the
`rectifying element 204,