US007211986B1
`
`a2) United States Patent
`Flowerdew etal.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,211,986 B1
`May1, 2007
`
`(54)
`
`INDUCTIVE CHARGING SYSTEM
`
`(75)
`
`Inventors: Peter M. Flowerdew, Brentry (GB);
`David Huddart, Westbury-on-Trym
`(GB)
`(73) Assignee: Plantronics, Inc., Santa Cruz, CA (US)
`.
`:
`‘
`‘
`ee
`(3) Mavce::
`-Subjent to-any disclamaen, ie tecancit ths
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 106 days.
`
`G/199G WINN vocsseserscsecessceccenee 417/436
`5,522,712 A
`LOMOO8! Bekouisus niin S65/26
`Soa, fou *
`2/1997 Goto
`5,600,225 A
`3/1998 Stephens ........s000.s.04. 320/106
`5,734,254 A *
`6,134,420 A ® L0/2000 Flowerdew etal cay 455/41.1
`6,549,379 BL*
`4/2003 Kazmierezak et al.
`.... 360/264.8
`*
`if
`i
`J
`Sea ee
`SEEREE BliOiceenaeonctorecanoanve en IF
`6,798,173 B2*
`9/2004 Hsu ....
`wees 320/134
`6,803,744 BL* 10/2004 Sabo...
`cece 320/108
`
`2004/0145342 Al® 7/2004 pa saintscinsesseneavitoe BOOT VOB
`* cited by examiner
`
`(21) Appl. No.: 10/882,961
`
`(22)
`
`Filed:
`
`Jul. 1, 2004
`
`(51)
`
`Int. Cl.
`(2006.01)
`HO2J 7/00
`“UiSi Cli sisiieniioniieniceininpuomng AeOALOS
`(52))
`(58) Field of Classification Search................. 320/107,
`320/108, 110, 112, 113, 114, 115, 116
`See application file for complete search history.
`ps
`References Cited
`U.S. PATENT DOCUMENTS
`
`(56)
`
`sy
`3,840,795 A . ve Roszyk et al.
`3,938,018 A
`2/1976 Dahl
`.sssseesserresvesrevsees 320/140
`
`4,873,677 A * 10/1989 Sakamoto et al.
`.......... 368/204
`SAO 793: A STOOD OG cance naseavsesarveaece
`sense 320/108
`sees 455/573
`5,396,538 A *
`3/1995 Hong ...
`
`....cceccseseeeesesees 455/573
`SAT9A8G A * 12/1995 Saji
`
`Primary Examiner—Karl Easthom
`Assistant Examiner—Samuel Berhanu
`(74) Attorney, Agent, or Firm—Thomas Chuang
`
`(57)
`
`ABSTRACT
`
`An apparatus for inductive charging a battery. The apparatus
`includes a housing with a lower surface and a charging
`surface. A rechargeable device with a rechargeable battery
`may be placed onthe charging surface. The apparatus further
`includes a controller for driving an oscillator, wherein the
`controller receives power from a power source. A first
`charger coil and second charger coil are disposed within the
`housing and are coupled to the oscillator, The first charger
`coil and second charger coil create a substantially horizontal
`magnetic field in the volume of space above the charging
`surhice
`nee
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`52 Claims, 12 Drawing Sheets
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`U.S. Patent
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`May1, 2007
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`U.S. Patent
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`U.S. Patent
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`US 7,211,986 Bl
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`1
`INDUCTIVE CHARGING SYSTEM
`
`TECHNICALFIELD
`
`field of
`invention relates to the general
`The present
`charging interfaces. More specifically the invention relates
`to inductive battery chargers.
`
`ay
`
`BACKGROUND
`
`30
`
`2
`station contacts press into the depressions in the recharge-
`able device contacts. However, this solution compromises
`the industrial design of the rechargeable device, and in
`addition the detent force is less than robust.
`As electronic items become smaller and the regulatory
`requirements become more stringent,
`the charging port
`becomes more noticeable as a relatively large unattractive
`feature of the housing, as an ESD weakness, as a relatively
`unreliable element in the system.
`In the prior art, contactless battery chargers have also
`been utilized. The use of inductive coupling used for con-
`tactless powertransfer betweenelectrical items is described
`in the prior art. The magnetic field generated by onecoil is
`made to couple closely with that of a second coil. Changes
`in the field induce a voltage in the second coil hence power
`transfer is possible. Inductive charging is discussed in U.S.
`Pat. No. 3,840,795, Electric Toothbrush, U.S. Pat. No.
`3,938,018, Chargerfor electronic items, U.S. Pat. No. 4,873,
`677, Rechargeable watch. Basic inductive charging compo-
`nents are available from companies such as Panasonic and
`TDK.
`
`FIG, 1 illustrates a typical prior art arrangement to ensure
`close coupling as disclosed in U.S, Pat. No. 5,600,225. In
`this arrangement, mechanical coupling between the charger
`and radiotelephoneis required. The charger 1 for supplying
`powerfor charging to the radiotelephoneis installed within
`a base case 101. A depression 102 into whichthe radiotele-
`phone may be inserted is provided on the upper surface of
`the base case 101, and a primary coil 103 is provided in the
`base case 101 for producing magnetic flux which mins
`around the side walls of the depression 102 in a vertical
`plane. This primary coil 103 is connected to an oscillating
`circuit for supplying alternating current to the coil.
`The radiotelephone 2 is provided with a microphone 202,
`a console keyboard 203, a display 204, a receiver 205, and
`an antenna 206 mounted on a slender telephone case 201.
`Inside the telephone case 201 is a storage battery. The
`storage battery is connected to a secondary coil 212 by way
`of an AC-DC conversioncircuit.
`The baseof the telephone case 201is constructed to allow
`insertion into the depression 102 provided in the base case
`101, and in this way the radiotelephone 2 may be placed on
`the charger 1 in an erect state. The secondary coil 212 is
`provided within the base portion of the case 201 ofthe
`radiotelephone2.
`To operate,
`the radiotelephone 2 is placed upon the
`charger 1 when the storage battery is to be charged. At this
`time, the radiotelephone2 is held in an erectstate by means
`ofinsertion of the base portion ofthe telephone case 201 of
`the radiotelephone 2 into the depression 102 provided in the
`base case 101 ofthe charger 1. An alternating current signal
`of prescribed frequency generated in this oscillating circuit
`is suppliedto the primary coil 103. As a result, an alternating
`magnetic field is generated by the primary coil 103 within
`the depression 102 in the base case 101 of the charger 1. This
`alternating magnetic field generates an induced electromo-
`tive force in the secondary coil 212 arranged in the base
`portion ofthe telephone case 201 ofthe radiotelephone 2.
`Theprior art device described in reference FIG. 1 as well
`as other prior art solutions require mechanical coupling
`between the charger and device to be charged. To make the
`efficiency of powertransfer as high as possible it is neces-
`sary to contain the magnetic field so thatall, or most, of the
`field in the first coil is linked to the second. To achieve this
`
`is typically necessary to provide some close mechanical
`it
`coupling such that there is a form of “plug” and “receptacle”
`arrangement. Contactless charging has been restricted to
`
`Wireless headsets and other portable communications
`devices are often battery powered such that a user can use
`the wireless headset or other such device without being
`directly connected to larger power source such as an a/c
`outlet or automobile battery. This allows wireless headset
`users flexibility and convenience to move about without
`being tied to a power cord. Wireless headset batteries are
`generally rechargeable so that the batteries can be recharged
`and need not be discarded after use.
`J
`Recharging of device batteries has generally achieved by 3
`a wired connection. In the prior art, devices employing
`rechargeable batteries typically have charging contacts so
`that charging current power can be supplied to recharge the
`batteries without removing the batteries from the device. In
`one typical setup, the portable device is inserted into a base
`charger which has spring loaded contacts that correspond to
`and couple with the contacts on the portable device, For
`example, such a setup is used with remote handset phones
`used in the home. The base charger is connected to a power
`source, and supplies charging current through the coupled
`contacts to recharge the batteries located within the device.
`Spring-loaded surface wiping contacts are generally used
`with charging bases. This is a convenience feature as users
`can simply drop the portable device into a cradle without
`fumbling with a plug. Surface contacts can be placed on the
`side of a taper form headset or other portable rechargeable
`device, making docking into a cradle mucheasier than a
`plug.
`However, use of surface contacts and a charging base
`station with a headset presents problems due to the smaller
`physical size and designofheadsets. Exposed metal contacts
`on headsets also risk contamination by oils and moisture
`from the skin of the wearer. This may cause corrosion and
`hence poorcontact with the base station. Contamination also
`may cause anelectrical leakage path that may cause power
`loss fromthe battery and electrolytic activity. Exposed metal
`contacts may alsoresult in an allergic reaction to the userif
`in prolonged contact with the user’s skin. During the
`rechargeable device docking process, the formed ends ofthe
`base station charging contacts often come into contact with
`the plastic housing of the rechargeable device and can
`scratch the housing and pick up contamination which can
`cause intermittent electrical contact. One potential solution
`is to cut the rechargeable device housing away to fully
`expose the rechargeable device stationary contacts so that
`the spring loaded contacts of the base station never touched
`the plastic housing during docking. However, this solution
`may compromise the rechargeable device industrial design,
`aesthetics, and possibly weaken the rechargeable device
`structural integrity.
`Furthermore,
`the headset or other rechargeable device
`may not be firmly detented with the charging base, which
`may also cause intermittent electrical contact. One potential
`solution to the weak coupling between the portable
`rechargeable device and charging base to dishthe stationary
`contacts in the rechargeable device so that the rechargeable
`device detents when the ends of the spring loaded base
`
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`US 7,211,986 Bl
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`ay
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`3
`“mating pairs’ in that the item to be charged and the charger
`are designed as a pair
`to achieve a closely controlled
`mechanical alignment of the coils in each unit, to maximize
`efficiency. This meansthat generally these charging methods
`are customdesigned for the appliance due to non standard-
`ization of the interface and can require dexterity to use. The
`costs ofthe design ofthe charging systemandthe additional
`mechanical design have to be bornby the individual product.
`This has restricted the adoption of contactless charging
`systems. Removing the requirement for accurate mechanical
`alignment would allow one charger design to be used across
`a range of products, allowing the development costs to be
`born by the range of products and reducing the design time
`for the introduction of a new product
`Furthermore, prior art solutions often allow charging of
`only one item at a time. Generally, a user has multiple
`rechargeable devices which require charging power. As a
`result, the user must transport or use a numberof chargers,
`generally one for each item. As the numberofdevices used
`J
`by an individual
`increases,
`the multiplicity of chargers 2
`becomes problematic.
`Thus,
`improved charging interfaces between charging
`base stations and rechargeable devices are needed.
`
`SUMMARY OF THE INVENTION
`
`4
`FIGS. 3A, 3B, and 3C are an illustration of horizontal
`coupling between a pancake coil and solenoidal coil.
`FIGS. 4A, 4B, and 4Care anillustration of a potential
`configuration of the components of a secondary unit con-
`taining a battery to be recharged.
`FIG. 5 illustrates a perspective view of an embodiment of
`the charging device of the present invention.
`FIG, 6 is a diagrammic view of the charger and the
`secondary unit.
`FIG. 7 is a diagrammic viewof a further embodiment of
`the charger.
`FIGS. 8A, 8B, and 8Cillustrate controllable permeability
`of the housing top surface of the charger.
`FIG, 9 is a diagrammic view of the charger with a
`controlled permeability housing top surface and the second-
`ary unit.
`FIG. 10 illustrate placement of the secondary unit on the
`surface of the charger.
`FIG. 11 illustrate the use of a directional logo on the
`charger.
`FIGS. 12A and 12B illustrate a chargerutilizing a rotating
`horizontal field.
`FIG. 13 is a circuit schematic illustrating variable tuning
`of a drive coil.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The present invention provides a solution to the needs
`described above through an inventive inductive battery
`charger.
`The present invention provides an apparatus for inductive
`charging a battery. The apparatus includes a housing with a
`lower surface and a charging surface. A rechargeable device
`with a rechargeable battery may be placed on the charging
`surface. The apparatus further
`includes a controller for
`driving an oscillator, wherein the controller receives power
`from a powersource, Afirst charger coil and second charger
`coil are disposed within the housing and are coupled to the
`oscillator. The first charger coil and second charger coil
`create a substantially horizontal magnetic field in the volume
`of space above the charging surface.
`The present inventionfurther provides a systemfor induc-
`tive charging whichincludes a charger. The charger includes
`a housing with a lower surface and a charging surface. A
`rechargeable device with a rechargeable battery may be
`placed onthe charging surface. The charger further includes
`a controller for driving an oscillator, wherein the controller
`receives power from a powersource. Afirst charger coil and
`second charger coil are disposed within the housing and are
`coupled to the oscillator. The first charger coil and second
`charger coil create a substantially horizontal magnetic field
`in the volume of space above the charging surface. The
`rechargeable device includes a receive coil for coupling to
`the horizontal magnetic field and producing an induced
`voltage. The rechargeable device further includes a rectifier
`for producing a rectified induced voltage to charge the
`battery in the rechargeable device.
`
`DESCRIPTION OF THE DRAWINGS
`
`The features and advantages ofthe apparatus and method
`of the present invention will be apparent fromthe following
`description in which:
`FIG. 1 is anillustration of a prior art induction charging
`system
`FIG, 2 is a circuit diagram partly in block form ofa
`charging system in accordance with an embodiment of the
`invention.
`
`30
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`The present invention provides a solution to the needs
`described above through an inventive inductive battery
`charger.
`Other embodiments of the present invention will become
`apparent
`to those skilled in the art
`from the following
`detailed description, wherein is shown and described only
`the embodiments ofthe invention by way ofillustration of
`the best modes contemplated for carrying out the invention.
`As will be realized, the invention is capable of modification
`in various obvious aspects, all without departing from the
`spirit and scope ofthe present invention. Accordingly, the
`drawings and detailed description are to be regarded as
`illustrative in nature and notrestrictive.
`The present invention provides a contactless charging
`systemutilizing induction which does not require a housing
`with a compartment or recess that must be mechanically
`matched to the item being charged. This creates the oppor-
`tunity to charge a variety of battery powered electronic items
`from a single charger. Further, the charging system lends
`itself to the simultaneous charging of dissimilar items.
`In an embodimentof the invention, the charger takes the
`form of a shallow concave (herein also referred to as
`“dished” or a “dish”) or similarly shaped upper charging
`surface, which whilst substantially flat and thin, develops a
`magnetic field which is substantially horizontal rather than
`perpendicular to its surface, which is typically the caseif a
`coil were wound in the same planeas a plate. By developing
`an angled field that is substantially horizontal, it is possible
`to couple energy to a receiver coil comprising a long
`solenoid,
`lying horizontally on the upper surface of the
`charger.
`Referring to FIG. 2, a circuit diagrampartly in block form
`ofa charging systemincluding a charger 302 (also referred
`to herein as a primary unit or base unit) and secondary unit
`304 (also referred to herein as a device to be charged or unit
`under charge) are shown. Circuit diagram elements are
`mounted ona printed circuit board disposed within charger
`302 and secondary unit 304. Secondary unit 304 includes a
`rechargeable battery 320 to be charged by charger 302.
`
`15
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`US 7,211,986 Bl
`
`5
`Secondaryunit 304 may be any small electronic device with
`a battery to be recharged. For example, secondary unit 304
`may include wireless headsets, mobile telephones, personal
`digital assistants (PDAs), cameras, or other such devices.
`Charger 302 is designed to draw power from a power
`source 306 such as a standard electrical wall outlet.
`In a
`further embodiment power source 306 may be an auxiliary
`power source from another piece ofelectronic equipment,
`such as through a USB port on a personal computer. Charger
`302 may be linked to the personal computer via the USB
`port to provide data derived from communication with one
`or more secondary units 304 to the computer for display.
`Where secondary unit 304 is a small item such as a wireless
`headset or cordless mouse, an auxiliary power source can
`provide sufficient charging power.
`Referring to FIG. 2, there is shown power source 306
`connected to a controller 308 for driving an oscillator 310.
`Controller 308 may include a rectifier. Oscillator 310 pro-
`vides a high frequency A.C. signal to drive a chargercoil.
`The frequency of the A.C. signal may vary. The lower limit
`for a practical operating frequency is determined by the
`higher field strength and/or larger coils required in the
`primary and secondary units. A higher frequency desirably
`facilitates the use of a smaller coil in the unit being charged.
`The upper limit on a practical operating frequency is deter-
`mined by either the energy dissipated in the metallic content
`of the unit being charged, primarily the copper layers of a
`PCB, or by reaching the self-resonant frequency of any of
`the coils. These limits are therefore defined in practice by the
`volumes available for the coils,
`the power that must be
`transferred, the allowable internal temperature of the unit
`being charged and the efficiency required in the system. The
`frequency representing the best compromise between these
`differentcriteria is approximately in the range from 8 kHz to
`300 kHz. In an embodiment of the invention, the preferred
`operating range is between 10 kHz and 40 kHz. The high
`frequency signal may be raised or lower depending upon the
`specific application. A charger coil (also referred to herein as
`a drive coil) takes the form in the particular embodiment
`illustrated of charging coil 312 and charging coil 314
`connected to oscillator 310. As described in further detail
`below, charging coil 312 and charging coil 314 are disposed
`at an angle to each other to direct the path of the generated
`electromagnetic field in a desired manner to enable horizon-
`tal coupling.
`Shownin proximity to charger 302 is secondary unit 304.
`Secondary unit 304 includes a secondary unit coil 316 (also
`referred to herein as a receive coil), which may include a
`permeable material core. During charging, secondary unit
`304 is placed near charger 302 so that the magnetic flux from
`the magnetic field created by charging coil 312 and charging
`coil 314 passes through the secondary unit coil 316. The
`positioning of secondary unit coil 316 is such as to provide
`for maximum flux coupling of the electromagnetic field
`provided from the angular arrangement ofthe charging coil
`312 and charging coil 314. Consequently, the magnetic flux
`induces a voltage across coil 316 resulting in an induced
`current to charge battery 320. A meter may be connected
`across the secondary unit coil 316 to provide a visual
`indication of the degree of coupling.
`Within secondary unit 304, the secondary unit coil 316
`connects to a rectifier which serves as an A.C.
`to D.C.
`converter. Althoughillustrated as a rectifying diode 318, the
`rectifier may be implemented by other means. For example,
`a custom ASIC providing synchronousrectification to mini-
`mize voltage drops may be used. Rectifying diode 318
`provides a D.C. charging signal to battery 320, which is
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`connected in series between secondary unit coil 316 and
`rectifying diode 318. Battery 320 serves as a power source
`for secondary unit 304. Charging is accomplished with a
`constant current. A regulator circuit may be employed to
`charge battery 320 to a certain capacity and then convert the
`charging current
`to a trickle type charge. The regulator
`circuit
`is responsive to the temperature and voltage of
`battery 320 to limit the charging current. The description of
`charger 302 and secondary unit 304 has been described in
`reference to the simplified circuit diagram shownin FIG. 2
`for clarity. Other circuit elements and arrangements may be
`utilized by charger 302 in order to provide alternating
`current flow to charging coil 312 and charging coil 314.
`One feature of the invention is a charger 302 which
`generates an essentially horizontal magnetic field and the
`use of a long solenoidal coil 326 to receive this field. FIGS.
`3A, 3B, and 3C are an illustration of horizontal coupling
`between a pancake coil 322 and solenoidal coil 326. The
`EMF induced in a coil depends strongly on the anglethat it
`makes to the magnetic field. Referring to FIG. 3A,
`the
`maximum possible induction (coupling) occurs when the
`field passes through the coil. This occurs when thedirection
`of the field is orthogonal to the plane of the coil. Illustrated
`in FIG. 3A is maximuminductionfor a pancake coil 322 and
`a solenoidal coil 322 from a horizontal field 324. This
`arrangement forms the basic geometry of a charger 302
`utilizing a horizontal field.
`Referring to FIG. 3B, if the pancake coil 322 or solenoidal
`coil 322 is rotated by 90° around a vertical axis, there is no
`flux through the coil, and no induced EMF. With a pancake
`coil 322 the decrease from full coupling to zero coupling
`follows a sinusoidal curve. The change in coupling for a
`cored solenoidal coil 326is less well defined but tendsto be
`more linear. A 30° rotation from maximum coupling results
`in approximately 14% reduction in induced EMF fora short
`coil and 30% reductionin the output of a winding on a long
`thin core. Referring to FIG, 3C, the induced voltage as a
`function of angle tothe field for a pancake coil 328 and long
`solenoid coil 330 is shown.
`FIGS. 4A, 4B, and 4Care anillustration ofa potential
`configuration of the components of a secondary unit con-
`taining a battery to be recharged. The configuration is
`advantageously arranged to allow for easy placement of the
`secondary unit on charger 302 while still providing for the
`desired horizontal field coupling.
`Referring to FIG. 4A, hand held secondary units having a
`housing 340 with length 334, width 332 and thickness 336
`would normally be placed ona flat surface, such as a desk,
`with the dimension indicated as thickness 336 in the vertical
`
`plane. For ergonomic reasons it is usual to arrange a battery
`320 in such a secondary unit suchthat the battery major axis
`is in the horizontal plane and a PCB 338 carrying the
`electronic circuits would also generally be in the horizontal
`plane. The inventive system advantageously utilizes a coil
`woundona long, thin permeable core (a solenoidal winding)
`as the inductive elementto receive energy from a horizontal
`field in the secondary unit being charged. Use ofa solenoidal
`winding is possible because the charger generates a substan-
`tially horizontal field. With some shapes of housing there
`may be advantageto rotating the coil in the horizontal plane
`and/ortranslating it vertically.
`FIG. 4Billustrates the geometryassociated with charging
`with a singular direction horizontal field 346 whilst FIG. 4C
`illustrates the implications of using a singular direction
`vertical field 348. Coil windings are placed underthe battery
`in an embodiment of the invention. Referring to FIG. 4B,
`when charging is conducted with a horizontal field 346, a
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`vertical dimension, discrete charging coils 312 and 314 may
`be positioned adjacent to the concave surface at varying
`inward angles with respect to a vertical axis to generate the
`desired horizontal field. Raising and angling charging coil
`312 and charging coil 314 places the coil center-lines closer
`to the axis of the solenoid, thereby providing for improved
`coupling.
`FIG. 6 is a diagrammic view of a charger 302 and
`secondary unit 304. FIG. 6 illustrates an exemplary physical
`arrangement of a charger 302 of the inductive charging
`system. Charger 302 includes a housing structure 356 defin-
`ing a charging surface 357 advantageously shaped to receive
`a secondary unit 304 incorporating a rechargeable battery
`320. Controller 308 andoscillator 310 described in reference
`
`7
`solenoidal winding on a high permeability core 342 may be
`utilized. The use of a high permeability core advantageously
`allows a high induced voltage in the solenoidal coil. The
`effective permeability of a magnetic coreis a direct function
`of the ratio ofits length to its diameter, so a long thin core
`couples more effectively to a field than a short flat one. Also
`advantageously, battery 320 and PCB 338 are in a separate
`magnetic flux path, thereby minimizing the effect on the coil
`Q. However, in a singular direction horizontal field 346, a
`rotation of solenoidal winding on permeable core 342 in the
`horizontal plane will produce a coupling null.
`Referring to FIG. 4C, when charging is conducted with a
`singular directionvertical field 348, a low permeability core
`is utilized resulting disadvantageously in a low induced
`to FIG, 2 are disposed within housing structure 356 (not
`voltage. Furthermore, battery 320 and PCB 338 are in the
`shown).
`same magnetic flux path, producing the potential for high
`Charger 302 may also contain additional components
`loss. Advantageously, when a vertical field 348 is used, there
`typical of battery charging devices. For example, charger
`is no coupling null with rotation of the coil in the horizontal
`302 may always be in a poweronstatus, or alternatively may
`plane.
`J
`include a manually operated on/off button for turning the
`Neither the singular direction vertical field 348 nor the 2
`charger power on and off. Charger 302 mayalso include an
`singular direction horizontal field 346 delivers the ideal set
`indicatorlight such as a light emitting diode whichserves as
`ofcharacteristics. However, since efficient coupling is the
`an indictor of the powerstatus. Secondary unit 304 may also
`most important requirement in a charger, a horizontal field
`include anindicator light coupled to a secondary unit 304
`is preferred. Furthermore, as described below, charger 302
`control circuit which indicates charging status.
`generates a horizontal field and advantageously is designed
`To operate, the secondary unit 304 is placed upon charger
`with a rotating horizontal field so that a coupling null does
`302 whenthe battery 320 in secondary unit 304 is in need
`not result with horizontal rotation of the secondary unit. The
`of charging. The secondary unit 304 is placed on charging
`charging system of the present invention advantageously
`surface 357 provided on charger 302. Charger 302 is then
`provides for a high permeability core so high induced
`connected by way of a power cord to an external power
`voltage in charging coil, no null with rotation in the hori-
`source 306. When charger 302 is in a poweronstate, power
`zontal plane, and a battery and PCBin a separate flux path
`controlled by controller 308 is supplied to oscillator 310. An
`so there is a low effect on coil Q.
`alternating current signal of prescribed frequency generated
`FIG. 5 is a perspective view of charger 302 showing a
`in oscillator 310 is supplied to charging coil 312 and
`housing 356 with a lower surface 359 and a charging surface
`charging coil 314. As a result, an alternating magnetic field
`357 on which secondary units are placed for charging.
`is generated by charging coil 312 and charging coil 314
`Although illustrated in a block housing in FIG. 5, lower
`above charging surface 357 of charger 302.
`surface 359 and charging surface 357 may be incorporated
`The alternating magnetic field generates an induced elec-
`into a variety of housing shapes, including a configuration
`with raised sides as illustrated in FIG. 7. Lower surface 359
`tromotive force in the secondary unit coil 316 arranged in
`the secondary unit 304. The alternating currentarising from
`is designed to act as a base whenthe unit is placed on a
`this induced electromotive force is converted to direct
`horizontal surface. Charging surface 357 is designed to
`current in an AC-DC conversioncircuit including rectifying
`receive items which will receive power from charger 302. In
`diode 318. The direct current power outputted from the
`an embodiment ofthe invention, charging surface 357 is a
`shallow concave surface in the vertical dimension 363.
`AC-DC conversion circuit constitutes a DC power source
`which may be applied to the battery 320 directly or, more
`Charging surface 357 is concave along the length dimension
`usually,
`through a charge control circuit, so causing the
`367 and along the width dimension 365, forming a dish or
`
`bow!like structure with a base surfaceparallel to the lower battery to be charged. Asaresult, battery 320 built into the
`surface 359. The depth of the dish is smaller than the
`secondary unit 304 is charged without being electrically
`dimensions of length dimension 359 or width dimension
`connected to charger 302.
`i.e.. while in an electrically
`365. In further embodiments, charging surface 357 is con-
`contactless state. The charger power may be turned offto
`cave in only the length dimension 367 or width dimension
`interrupt the magnetic circuit so that the secondary unit 304
`365 or flat. Charging surface 357 may include a plurality of
`may be easily removed from charger 302 when the charging
`dished recesses to permit the secure and defined location of
`is complete or when use of secondary unit 304 is desired.
`a plurality of items placed on the surface. The dished
`The arrangement is such that when secondary unit 304 is
`recesses may be optimized for the alignment of some subset
`placed on charging surface 357, the coil 316 within second-
`ofitems that are placed on the surface to receive power from
`ary unit 304 will be in flux coupling relationship with
`charger 302.
`In a further embodiment of the invention,
`charging coil 312 and charging coil 314.
`charging surface 357 possesses one or more markers indi-
`Referring to FIG. 6, disposed in the base of housing 356
`cating a preferred alignment and/ororientation for items that
`is a permeable material 358. Permeable material 358 serves
`several functions. Permeable material 358 increases the flux
`may placed onthat part of the surface to receive power from
`density in the area where secondary unit 304 is placed on
`charger 302.
`A feature of the invention is the provision of a shaped
`housing 356 and prevents flux from passing to metal struc-
`electromagnetic field to optimize coupling between charger
`tures on which charger 302 is placed and introducing losses,
`302 and secondary unit 304. As shownin FIG. 6,
`in an
`such as a filing cabinet or the metal frame of a bench.
`embodimentofthe inventio