WO2014130065A1

WO2014130065A1 - Variable pitch spiral coil

Info

Publication number: WO2014130065A1
Application number: PCT/US2013/031128
Authority: WO
Inventors: Joshua K. Schwannecke; David W. Baarman; Matthew J. Norconk; Ronald L. Stoddard; Joshua B. Taylor; Colin J. Moore
Original assignee: Access Business Group International LLC
Current assignee: Access Business Group International LLC
Priority date: 2013-02-25
Filing date: 2013-03-14
Publication date: 2014-08-28
Anticipated expiration: 2015-08-25
Also published as: TW201434063A; CN104008846A

Abstract

An inductive coil for a contactless power supply system is provided. The inductive coil includes a conductive element in a planar spiral pattern, wherein the pitch between adjacent spirals is greater near the center of the planar spiral pattern than near the outer periphery of the planar spiral pattern. The inductive coil can be used as any one of a primary coil, a primary side resonator coil, a secondary side resonator coil, and/or a secondary coil to increase the efficiency of a power supply system across a range of distances and alignment orientations. In some embodiments, the spirals are spaced apart from the center of the spiral pattern by a distance that increases in proportion to a square root curve, such that the spirals group together near the outer periphery of the spiral pattern.

Description

VARIABLE PITCH SPIRAL COIL

BACKGROUND OF THE INVENTION

[0001] The present invention relates to contactless power supply systems and more particularly to inductive coils for use in contactless power supply systems.

[0002] Contactless power supply systems include the transfer of electrical energy from a power supply to one or more portable devices without mechanical connection. A typical contactless power supply drives a time-varying current through a primary coil to create a time-varying electromagnetic field. One or more portable devices can each include a secondary coil. When the secondary coil is placed in proximity to the time-varying electromagnetic field, the field induces an alternating current in the secondary coil, thereby transferring power from the contactless power supply to the portable device.

[0003] It is generally desirable to improve power transfer between the primary coil and the secondary coil. Power transfer can be improved by varying a number of parameters. For example, power transfer can be improved by tuning the coupling coefficient— which relates to the relative geometry of the primary and secondary coils. Further by example, power transfer can be improved with the introduction of a ferrite core element, or with the addition of one or more resonator coils. For example, a contactless power supply can include a resonator coil and a portable device can include a resonator coil. In this four-coil configuration, the primary coil (L1) is paired with a resonator coil (L2), and the secondary coil (L4) is paired with a resonator coil (L3). The resonator coils (L2 and L3) cooperate to enhance inductive power transfer, particularly in mid-range applications.

[0004] Despite the above known techniques for improving power transfer, there remains a continued need to improve overall system efficiency for contactless power supply systems. In addition, there is a continued need to shorten the time required for a battery recharge by increasing the power transfer level, while also minimizing stray electromagnetic radiation from a contactless power supply. Improvements in efficiency to desired levels can potentially accelerate the adoption of contactless power supplies in electrical chargers, including for example electrical chargers for smartphones, tablet computers, laptop computers, personal digital assistants and other devices.

SUMMARY OF THE INVENTION

[0005] An inductive coil for a contactless power supply system is provided. The inductive coil includes a conductive element in a planar spiral pattern, wherein the pitch between adjacent spirals is greater near the center of the spiral pattern than near the outer periphery of the spiral pattern. The inductive coil can be used as any one of a primary coil, a primary side resonator coil, a secondary side resonator coil, and/or a secondary coil to increase the overall efficiency of a power supply system across a range of distances and alignment orientations, and for a range of contactless power supply applications.

[0006] In one embodiment, the inductive coil includes a conductive element in a planar spiral pattern, wherein the pitch between adjacent spirals of the planar spiral pattern progressively decreases with successive turns of the spiral pattern. The spirals are spaced apart from the center of the spiral pattern by a distance that increases in proportion to a square root curve, such that the spirals group together near the outer periphery of the spiral pattern.

[0007] In another embodiment, the inductive coil includes a conductive element in a planar spiral pattern having an innermost spiral, an outermost spiral, and a plurality of intermediate spirals, wherein the pitch between the innermost spiral and its adjacent spiral is greater than the pitch between any two adjacent intermediate spirals when measured along a radial extending from the center of the spiral pattern to the outer periphery of the spiral pattern.

[0008] In still another embodiment, the inductive coil includes a conductive element in a planar spiral pattern, wherein the pitch between adjacent spirals progressively decreases over a first portion of the spiral pattern, and wherein the pitch between adjacent spirals remains substantially constant over a second portion of the planar spiral pattern, the second portion being radially outward of the first portion.

[0009] In even another embodiment, the inductive coil includes a conductive element in a planar spiral pattern, wherein the pitch between adjacent spirals is greater in some areas than in other areas. In this embodiment, the pitch can increase over a first portion of the spiral pattern, and then decrease over a second portion of the spiral pattern before increasing again over a third portion of the spiral pattern. Conversely, the pitch can decrease over a first portion of the spiral pattern, and then increase over a second portion of the spiral pattern before decreasing again over a third portion of the spiral pattern.

[0010] In yet another embodiment, the inductive coil is a primary side resonator coil interposed between a power transfer surface and a primary coil. The resonator coil includes a conductive element in a planar spiral pattern, wherein the adjacent spirals having a first spiral density near the center of the spiral pattern less than a second spiral density near the outer periphery of the spiral pattern. In this embodiment, the primary coil is generally coextensive with the spirals nearer to the outer periphery, thereby reducing the coupling between the primary coil and a secondary coil positioned on or above the power transfer surface.

[0011] In a further embodiment, the inductive coil includes a conductive element in a circular spiral pattern, a square spiral pattern, an oval spiral pattern, a rectangular spiral pattern, a logarithmic spiral pattern, a fractal spiral pattern, including first and second order fractals, or other spiral pattern. The conductive element can include a conductive wire winding, a printed trace winding, a Litz wire, or other conductive element, optionally electrically connected in series with a capacitive element to provide a tuned resonant frequency. In addition, the inductive coil can include a core element, for example a ferrite core element, while in other embodiments the inductive coil can be free from any core, being generally coreless.

[0012] Embodiments of the invention can therefore provide an improved inductive coil for contactless power supply systems and other circuit devices, including for example drive electronics. When used as a primary coil or as a primary side resonator coil, the inductive coil enables wireless power to multiple devices over a larger area over known systems. In addition, the variable pitch spiral pattern can increase the minimum coupling coefficient in a target charging area, while also reducing the maximum coupling coefficient. This in turn enables the secondary coil to draw more power in the low coupling areas while having to suppress less overvoltage in the high coupling areas. This also enables the contactless power supply to detect more signals (e.g., communication signals) in lower coupling areas with less variation to average across the range of devices present.

[0013] These and other advantages and features of the invention will be more fully understood and appreciated by reference to the description of the current embodiments and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Fig. 1 is a plan view of an inductive coil in accordance with one embodiment.

[0015] Fig. 2 is a graph illustrating a spiral pattern following a square root curve.

[0016] Fig. 3 is a schematic diagram illustrating a contactless power supply system in accordance with one embodiment.

[0017] Fig. 4 is a cross-sectional diagram illustrating the contactless power supply system of

Fig. 3.

[0018] Fig. 5 is a prior art coil construction and portable device for performance comparison against the inductive coil of Fig. 1.

[0019] Fig. 6 is a two-dimensional coupling coefficient color plot for the prior art coil construction of Fig. 5.

[0020] Fig. 7 is a two-dimensional coupling coefficient color plot for the inductive coil of Fig. 1 lacking a ferrite core element.

[0021] Fig. 8 is a two-dimensional coupling coefficient color plot for the inductive coil of Fig. 1 including a ferrite core element. DESCRIPTION OF THE CURRENT EMBODIMENTS

[0022] The current embodiments relate to inductive coils for use in contactless power supply systems and other circuit devices. The inductive coil generally includes a conductive element in a planar spiral pattern, wherein the pitch between adjacent spirals is greater near the center of the spiral pattern than near the outer periphery of the spiral pattern. The inductive coil in accordance with one embodiment is discussed in Part I below. A contactless power supply system including an inductive coil in accordance with this embodiment is set forth in Part II below. An example is set forth in Part III below.

I. Inductive Coil

[0023] Referring now to Fig. 1 , an inductive coil in accordance with one embodiment is shown and generally designated 10. The inductive coil 10 includes a conductive element 12 having a first end portion 14 and a second end portion 16 defining a length therebetween. The conductive element 12 is arranged in a two-dimensional or planar spiral pattern including an approximate geometric center 18 and an outer periphery 20. The spiral pattern includes n number of spirals, wherein the outermost spiral is defined as the nth spiral or spiral-n, the next outermost spiral is defined as the n-1 spiral, and so on, until reaching the innermost spiral or spiral-1. As the term is used herein, a spiral (or turn) is defined to include that portion of the conductive element 12 traversing three hundred and sixty degrees about the geometric center 18. Any number of spirals can be used in a given embodiment, including for example greater than two hundred spirals. Also by example, the spiral pattern can include between two and two-hundred spirals inclusive, optionally between four and forty spirals inclusive, and further optionally between ten and twenty spirals inclusive.

[0024] As noted above, the spiral pattern includes a pitch between adjacent spirals. The pitch is a measurement of the distance separating the centerline of adjacent spirals. The pitch between adjacent spirals is different from the spacing between adjacent spirals, in that the spacing is equal to the pitch minus the conductor diameter or thickness. This distinction can be small or even negligible for conductors having a small diameter or thickness, in which instance the conductor 12 is assumed to be infinitesimally thin. In the present embodiment, the pitch between adjacent spirals is greater near the center 18 of the spiral pattern than near the outer periphery 20 of the spiral pattern. For example, the pitch progressively decreases over a first portion 22 of the spiral pattern, and remains substantially constant over a second portion 24 of the spiral pattern radially outward of the first portion 20 of the spiral patter. In this regard, the first portion 24 of the spiral winding includes a progressive decrease in spiral pitch, while the second portion 24 of the spiral winding includes a substantially constant spiral pitch. In other embodiments, however, the spiral pattern includes a progressive decrease in pitch from the center to the outer periphery, and does not include the second portion 24 having a substantially constant pitch.

[0025] The spiral pattern can also be described based on the distance to the spiral pattern center 18. For example, the distance to the spiral pattern center 18 can progressively increase in accordance with a square root curve. That is, at each point along an arbitrary radial 26 extending from the center 18 (e.g., the 270° radial), the distance to the spiral pattern center 18 increases in proportion to the square root of n, where n corresponds to the spiral number. Numerical values in accordance with one embodiment are shown below for an eight inch by eight inch square spiral pattern with an inductance of 35.58 μΗ, and graphically depicted in Fig. 2:

[0026] To reiterate, the spiral pattern includes a repeating pattern of spirals each defining a distance to the center of the spiral pattern when measured along a common radial, wherein the distance is proportional to the square root of that number spiral. In the embodiment shown in Figs. 1-2 above, for example, the distance for each spiral is determined by multiplying the square root of n by a proportioning constant c, where c is optionally equal to the distance between spiral-1 and the spiral pattern center 18, or 1.24 inches in the present embodiment. This equation is depicted below:

(1 ) distance to center = c * sqrt (n)

Using equation (1), the distance for each spiral can be computed along a common radial, for example the negative-x axis as shown in Fig. 2. Different radials can be used in addition to this radial. For example, a rectangular spiral pattern can include a different distance in the y-direction. Using equation (1) above, the y-distance is equal to the square root of each n turn multiplied by the constant c, where c is optionally equal to the y-distance for spiral-1.

[0027] As optionally illustrated in Fig. 1 , an additional spiral 28 is included between spiral-11 and spiral-12, with this additional spiral not following the square root curve of Fig. 2. Instead, the additional spiral 28 is spaced substantially equally between spiral-11 and spiral-12, such that these three spirals form the second portion 24 of substantially constant spiral pitch. Further optionally, the spiral pattern can assume essentially any planar geometry, including for example a square spiral or a rectangular spiral as generally depicted in Fig. 1. Alternatively, the spiral pattern can include a single continuous curve, including for example an oval spiral or a circular spiral. In other embodiments the spiral pattern can assume different geometries as desired. For example, the spiral pattern can include a logarithmic spiral pattern or a fractal spiral pattern, for example a first order fractal or a second order fractal, which can potentially generate a smooth flux field density. In addition, the spiral pattern can be formed of essentially any conductive material, including for example Litz wire, copper wire, etched conductors or printed conductors.

II. Contactless Power Supply System

[0028] As noted above, the inductive coil 10 is suitable for use in contactless power supply system, and in other circuit devices. For example, the inductive coil 10 can be used in conjunction with a contactless power supply system 30 having a contactless power supply 32 and one or more portable devices 34, 36, generally depicted in Figs. 3-4. The contactless power supply 32 can include a primary coil 38 and a primary side resonator coil 40, while the portable devices 34, 36 can optionally include a secondary side resonator coil 42 and a secondary coil 44. As set forth below, any or all of these inductive elements 38, 40, 42, 44 can include the inductive coil 10 of the present invention.

[0029] More particularly, the contactless power supply 32 includes a power supply 46, signal generating circuitry 48 (depicted as an inverter), a wireless power transmitter 50, and a control system 52. The power supply 46 of the current embodiment may be a conventional power supply that transforms an AC input (e.g., wall power) into an appropriate DC output that is suitable for driving the wireless power transmitter 50. As an alternative, the power supply 46 may be a source of DC power that is appropriate for supplying power to the wireless power transmitter 50. In this embodiment, the power supply 46 generally includes a rectifier 54 and a DC-DC converter 56. The rectifier 54 and DC- DC converter 56 provide the appropriate DC power for the power supply signal. The power supply 46 may alternatively include essentially any circuitry capable of transforming input power to the form used by the signal generating circuitry 48. The control system 52 can be configured to adjust operating parameters. For example, the control system 52 may have the ability to adjust rail voltage or switching circuit phase. In an alternative embodiment where it is desirable to adjust operating parameters by varying the rail voltage, the DC-DC converter 56 may have a variable output. As shown in Fig. 3, the adaptive control system 52 may be coupled to the DC-DC converter 56 (represented by broken line) to allow the adaptive control system 52 to control the output of the DC-DC converter 56.

[0030] The signal generating circuitry 48 includes switching circuitry that is configured to generate and apply an input signal to the wireless power transmitter 50. The switching circuitry may form an inverter that transforms the DC output from the power supply 46 into an AC output to drive the wireless power transmitter 50. The switching circuitry may vary from application to application. For example, the switching may include a plurality of switches, such as MOSFETs, arranged in a half- bridge topology or in a full-bridge topology. The power transmitter 50 includes a tank circuit 58 having a primary coil 38 and a ballast capacitor 60 that are arranged to form a series resonant tank circuit and a resonator circuit 62 having a resonator coil 40 and a resonator capacitor 64. The term primary circuit may be used to refer to the entire tank circuit 58 or to the primary coil 38. The term primary resonator circuit may be used to refer to the entire resonator circuit 62 or to the resonator coil 40. The present invention is not limited to use with series resonant tank circuits and may instead be used with other types of resonant tank circuits and even with non-resonant tank circuits, such as a simple inductor without matching capacitance. And, although the illustrated embodiment includes coils, the contactless power supply 32 may include alternative inductors or structures capable of generating a suitable electromagnetic field.

[0031] The control system 52 includes portions configured, among other things, to operate switching circuitry to produce the desired power supply signal to the wireless power transmitter 50. The adaptive control system 52 may control the switching circuitry based on communications received from the remote device 34, 36. The adaptive control system 52 of this embodiment includes control circuitry that performs various functions, such as controlling the timing of the switching circuit and extracting and interpreting communications signals. These functions may alternatively be handled by separate controllers or other dedicated circuitry.

[0032] As shown in Fig. 4, the contactless power supply 32 additionally includes a power transfer surface 82 to receive the portable devices 34, 36 at a plurality of locations along the power transfer surface 82, such that the portable devices 34, 36 have spatial freedom in two dimensions. In this configuration, the primary coil 38 is located transverse to the resonator coil 40. In addition, the primary coil 38 and the primary side resonator coil 40 share a coupling coefficient greater than the coupling coefficient shared between the primary coil 38 and either of the secondary coil 44 or the secondary side resonator coil 42. An optional shield 83 is interposed between the primary coil 38 and the resonator coil 40. The shield is generally positioned such that certain coupling is unhindered while other coupling is reduced. In some embodiments, the shield 83 is a flux concentrator or flux guide. In other embodiments, a portion of the shield 83 is a flux concentrator. An optional core element 85 is positioned in the center of the spiral pattern, potentially smoothing the coupling coefficient over a greater area. In addition, while only six spirals are depicted in Fig. 4, the primary side resonator coil 40 can include any number of spirals, including for example thirteen spirals as depicted in Fig. 1.

[0033] The portable devices 34, 36 in accordance with an embodiment of the present invention will now be described in more detail. The portable devices 34, 36 may include a generally conventional electronic device, such as a cell phone, a media player, a handheld radio, a camera, a flashlight or essentially any other portable electronic device. The portable device 34, 36 may include an electrical energy storage device, such as a battery, capacitor or a super capacitor, or it may operate without an electrical energy storage device. The components associated with the principle operation of the portable device 34, 36 (and not associated with wireless power transfer) are generally conventional and therefore will not be described in detail. Instead, the components associated with the principle operation of the portable device 34, 36 are generally referred to as principle load 66. For example, in the context of a cell phone, no effort is made to describe the electronic components associated with the cell phone itself.

[0034] The portable device 34, 36 of this embodiment generally includes a wireless receiver

68, a rectifier 70, a secondary communications transceiver (not shown), and a principle load 66. The portable device 34, 36 may include a controller. The wireless receiver 68 may include a secondary tank circuit 72 having a secondary coil 44 and secondary tank capacitor 74 and a secondary resonator circuit 76 having a secondary resonator coil 42 and secondary resonator capacitor 78. The term secondary circuit may refer to the secondary tank circuit or the secondary coil. In some embodiments, the wireless receiver 68 may not include a secondary tank capacitor. The term secondary resonator circuit may refer to the entire secondary resonator circuit or the secondary resonator coil. In some embodiments, the portable device may not include a secondary resonator circuit 76, including for example the portable device 36 shown in Fig. 3. The present invention is not limited to the topology of the wireless receiver 68 of the illustrated embodiment in Fig. 3. Alternative embodiments, for example, may include both a secondary tank circuit 72 and a secondary resonator circuit 76 coupled to the rectification circuitry 70 of the portable device rather than the secondary resonator circuit 76 being isolated from the secondary tank circuit 72 as shown in the illustrated embodiment of Fig. 3.

[0035] The rectifier 70 and regulation circuitry 80 convert the AC power generated in the wireless power receiver 68 into power for operation of the load 66. The regulation circuitry 80 may, for example, include a DC-DC converter in those embodiments where conversion to and regulation of DC power is desired. In applications where AC power is desired in the portable device 34, 36, the rectifier 80 may not be necessary. In some embodiments, regulation circuitry may be unnecessary or implemented as part of the load 66. Although not illustrated, the portable device 34, 36 may include a secondary communications transceiver adapted to modulate and demodulate information via the wireless power link with the contactless power supply 32. Alternatively, a separate communication channel can be set up between the portable device and contactless power supply, the functions of which may be handled by separate controllers or other dedicated circuitry. The contactless power supply 32 and portable device 34, 36 may be configured to communicate using essentially any data encoding scheme.

[0036] In addition to the contactless power supply system set forth above in connection with

Figs. 3-4, the present invention may be incorporated into the contactless power supply disclosed U.S. Patent 7,212,414, which is entitled "Adaptive Inductive Power Supply" and issued May 1 , 2007, to Baarman; the contactless power supply with communication of U.S. Patent 7,522,878, which is entitled "Adaptive Inductive Power Supply with Communication" and issued April 21 , 2009 to Baarman; the contactless power supply of U.S. Serial No. 13/156,390, which is entitled "Coil Configurations for Inductive Power Transfer" and filed June 9, 2011 , to Baarman; the contactless power supply of U.S. Serial Number 61/699,582, which is entitled "Wireless Power Control System" and filed September 11 , 2012, to Baarman; or the contactless power supply of U.S. Serial Number 61/699,643, which is entitled "Wireless Power Control" and filed September 11 , 2012, to Baarman— all of which are incorporated herein by reference in their entirety.

III. Example

[0037] The following example is provided for illustrative purposes and should not be construed as limiting. In particular, the following example includes a comparison of the inductive coil 10 of Fig. 1 against the prior art resonator coil 100 of Fig. 5. When paired with a secondary coil 102 in a portable device, the inductive coil 10 achieved a higher coupling coefficient nearer the center of the inductive coil 10, while also achieving a desired range of coupling coefficients across different portions of the inductive coil 10, which can be particularly advantageous for the simultaneous charging of multiple portable devices.

[0038] The prior art resonator coil 100 of Fig. 5 included an eight-turn double-layer winding with a height of 219 mm and a width of 222 mm. The receiver coil 102 used in this example included a single layer secondary coil having 15 turns of 40/40 Litz wire with a height of 31 mm and a width of 24 mm. The coupling coefficient k is depicted in Fig. 6, where the coupling coefficient is a scalar depiction of that portion of the flux originating from the resonator coil 100 and passing through the receiver coil 102. Of particular interest, the coupling coefficient k was strongest when the receiver coil 102 was positioned over the corners of the prior art resonator coil 100, achieving a peak coupling coefficient k of 0.085. By comparison, the coupling coefficient k farthest from the corner was between about 0.005 and about 0.01. In addition, the coupling coefficient k was predominantly about 0.005 to about 0.01 in central region of the resonator coil, e.g., the region greater than 2 cm from its outer periphery.

[0039] Using the same receiver coil 102, the coupling coefficient k was modeled for the inductive coil 10 of Fig. 1 both with and without a ferrite shield. In particular, the inductive coil 10 included a single-layer square spiral pattern having an inductance of 35.58 μΗ, an equivalent series resistance of 0.080 Ohms, and a capacitance of 45.0 nF. The inductive coil 10 included thirteen spirals, where spiral-1 through spiral-12 were spaced from the geometric center by a distance equal to the square root of the spiral number (i.e., 1 , 2, 3, 4 ... 12) multiplied by 1.24 inches. Spiral-11.5 was interposed between spirals 11 and 12 to provide close spaced turns on the outside of the inductive coil 10 to better accommodate energization by a transverse primary coil 38 as generally described above in connection with Fig. 4.

[0040] The primary coil 38 was driven with a time-varying current having an operating frequency of 126 kHz, generating a time-varying electromagnetic flux. This flux caused the resonator coil 10 to rapidly oscillate, optionally oscillating at resonance. The resonator coil 10 then induced a time-varying current in the receiver coil 102. The current induced in the receiver coil 102 varied based on the location of the receiver coil 102 relative to the geometric center 18 of the resonator coil 10. Referring now to Fig. 7, the coupling coefficient between the resonator coil 10 and the receiver coil 102 varied from about 0.060 near the corners of the resonator coil 10 to about 0.040 near the geometric center of the resonator coil 10. Thus, the resonator coil 10 of Fig. 1 demonstrated an improved coupling coefficient k over the resonator coil 100 of Fig. 6 in the central region of the coil. When a ferrite shield 83 was interposed between the primary coil 38 and the resonator coil 10, the coupling coefficient between the resonator coil 10 and the receiver coil 102 varied from about 0.065 near the corners of the resonator coil 10 to about 0.035 near the geometric center of the resonator coil 10, shown generally in Fig. 8.

[0041] As also depicted in Figs. 7-8, the range of coupling coefficients over the intended operating area was from 0.005-0.085 for the prior art resonator coil 100 and 0.015-0.065 for the inductive coil 10 of the present example. This narrowing of the range of available coupling coefficients can be particularly advantageous when the charging pad is coupled to multiple portable devices. For example, in many instances the "floor" coupling coefficient should be at least about 0.015 to permit a portable device to discriminate low-power communication signals from noise and other ambient interference. If a portable device were placed on a portion of a charging pad having a coupling coefficient less than 0.015, it is conceivable that the portable device would not identify the charging pad as such, and would therefore not initiate the communications handshake with the charging pad to begin wireless power transfer. Also by example, in many instances the "ceiling" coupling coefficient should not be undesirably high, in which instance the portable device would step down the over-voltage induced in the secondary coil. For example, a portable device can require the use of a DC-DC converter, e.g., a linear converter or a buck-boost converter, potentially increasing the size of the portable device in instances where a step down is required.

[0042] In a scheme in which two or more portable devices are placed on the charging pad, the narrowed range of available coupling coefficients can ensure that, at a minimum, each portable device will be able to communicate with the charging pad, independent of the position of the portable device on the charging pad. While this is happening, the remaining portable device can receive power elsewhere on the charging pad, without requiring additional circuitry to step-down an over-voltage induced in the secondary coil. Accordingly, the narrowing of available coupling coefficients enables portable devices to draw more power in low coupling regions while suppressing over-voltage in high coupling regions. The narrowing of available coupling coefficients also enables the charging pad to have less variation to average across the range of portable devices present.

[0043] The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described invention may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as an alternative. Further, the disclosed embodiments include a plurality of features that are described in concert and that might cooperatively provide a collection of benefits. The present invention is not limited to only those embodiments that include all of these features or that provide all of the stated benefits, except to the extent otherwise expressly set forth in the issued claims. Any reference to claim elements in the singular, for example, using the articles "a," "an," "the" or "said," is not to be construed as limiting the element to the singular.

Claims

1. A circuit device comprising:

a planar winding including a repeating spiral pattern, the repeating spiral pattern defining a pitch between adjacent spirals, wherein the pitch progressively decreases over a first portion of the planar winding, and wherein the pitch remains substantially constant over a second portion of the planar winding radially outward of the first portion of the planar winding.

2. The circuit device of claim 1 wherein the first portion pitch proportionally decreases moving radially outward along the planar winding.

3. The circuit device of claim 1 further including a primary winding located concentrically with respect to the planar winding.

4. The circuit device of claim 3 wherein the primary winding is generally coextensive with the second portion of the planar winding.

5. The circuit device of claim 3 wherein the primary winding is substantially free from overlap with the first portion of the planar winding.

6. The circuit device of claim 3 further including a power supply electrically connected to the primary winding and electrically isolated from the planar winding.

7. The circuit device of claim 3 wherein:

the planar winding is a resonating winding coupled to a secondary winding in a portable device; and

the planar winding and the secondary winding define a first coupling coefficient greater than a coupling coefficient defined between the primary winding and the secondary winding.

8. The circuit device of claim 1 wherein the repeating spiral pattern is one of a square winding, a rectangular winding, a circle winding, and an oval winding.

9. The circuit device of claim 1 further including a power transfer surface to receive a least one portable device thereon, the planar winding being substantially parallel to the power transfer surface.

10. The circuit device of claim 1 wherein the planar winding includes a printed conductive element, a coiled wire element, or an etched conductive element.

11. A contactless power supply comprising:

a power transfer surface to receive at least one portable device thereon; and

an inductive coil subjacent the power transfer surface, the inductive coil including a planar spiral winding defining a pitch between adjacent spirals, wherein the pitch progressively decreases radially outward of a central axis of the inductive coil.

12. The contactless power supply of claim 11 wherein the spirals are spaced apart from the central axis by a distance that increases in proportion to a square root curve, such that the adjacent spirals group together away from the central axis.

13. The contactless power supply of claim 11 further including a primary coil located subjacent the inductive coil.

14. The contactless power supply of claim 13 wherein:

the inductive coil forms part of a resonating circuit inductively coupled to a secondary coil in the portable device; and

the inductive coil and the secondary coil define a first coupling coefficient greater than a coupling coefficient defined between the primary coil and the secondary coil.

15. The contactless power supply of claim 14 wherein the resonating circuit includes a capacitor electrically connected in series with the inductive coil.

16. The contactless power supply of claim 13 further including a power supply coupled to the primary coil.

17. The contactless power supply of claim 11 wherein the inductive coil includes a square winding pattern, a rectangular winding pattern, a circular winding pattern or an oval winding pattern.

18. The contactless power supply of claim 11 wherein the inductive coil includes a ferrite core element.

19. The contactless power supply of claim 11 wherein the inductive coil includes a printed conductive element, a coiled wire element, or an etched conductive element.

20. A circuit device comprising:

a planar winding including a repeating spiral pattern having a center and an outer periphery, wherein a pitch between adjacent spirals of the planar winding is greater near the planar winding center than near the planar winding outer periphery.

21. The circuit device of claim 20 wherein the spirals are spaced apart from the planar winding center by a distance that increases in proportion to a square root curve, such that the spirals group together near the planar winding outer periphery.

22. The circuit device of claim 20 wherein the spiral coil includes n number of spirals, wherein n is between eight and eighteen.

23. The circuit device of claim 22 wherein the pitch between spirals n and n-1 is less than the pitch between spirals n-1 and n-2, wherein spiral n is the outermost spiral.

24. The circuit device of claim 20 wherein the repeating spiral pattern includes an innermost spiral and an outermost spiral, wherein the pitch between the innermost spiral and its adjacent spiral is greater than the pitch between the outermost spiral and its adjacent spiral when measured along a radial extending from the center to the outer periphery.

25. The circuit device of claim 20 wherein the repeating spiral pattern includes an innermost spiral, an outermost spiral, and a plurality of intermediate spirals, wherein the pitch between the innermost spiral and its adjacent spiral is greater than the pitch between any two adjacent intermediate spirals when measured along a radial extending from the planar winding center to the planar winding outer periphery.

26. The circuit device of claim 20 wherein the planar winding includes a printed conductive element, a coiled wire element, or an etched conductive element.

27. The circuit device of claim 20 wherein the repeating spiral pattern is one of a square winding, a rectangular winding, a circular winding, and an oval winding.

28. The circuit device of claim 20 further including a power transfer surface to receive a least one portable device thereon, the planar winding being substantially parallel to the power transfer surface.