GB2389720A

GB2389720A - Planar inductive battery charger

Info

Publication number: GB2389720A
Application number: GB0226893A
Authority: GB
Inventors: Ron Shu-Yuen Hui
Original assignee: City University of Hong Kong CityU
Current assignee: City University of Hong Kong CityU
Priority date: 2002-06-10
Filing date: 2002-11-18
Publication date: 2003-12-17
Anticipated expiration: 2022-11-18
Also published as: GB2389720B; GB0226893D0; GB0213374D0

Abstract

A battery charger system having a charging module with a planar charging surface 2 for receiving an electronic device 3 to be charged. The module includes a primary charging circuit having the primary winding of a transformer (fig. 4c). The primary winding is substantially parallel to the planar charging surface 2. The primary winding has electromagnetic shielding 5,6 on the side of the winding opposite the planar charging surface 2. The electronic device 3 includes a secondary winding.

Description

Hi t PLANAR INDUCTIVE}BATTERY CHART

FOLD OF IRE INVENTION

This invention relates to a battery charger, and in particular to a battery charger having a planar surface on which one or more battery powered devices may be placed 10 for battery recharging through induction.

BACKDROP OF THE MENTION

Portable electronic equipment such as mobile phones, handheld computers, personal data assistants, and devices such as a wireless computer mouse, are normally 15 powered by bateonos. In many cases, rechargeable batteries are preferred because of environmental and economical concems. The most common way to charge rechargeable batteries is to use a conventional charger, which nonnally consists of an AC-DC power supply (in case of using the ac mains) or a DC-DC power supply (in case of using a car battery). Conventional chargers normally use a cord (an electric 20 cable for a physical electrical connection) to connect the charger circuit (a power supply) to the battery located in the portable electronic equipment. The basic schematic of the conventional battery charger is shown in Fig.l.

PRIC)R ART

25 Inductive electronic chargers without direct physical electrical connection have been developed in some portable electronic equipment such as electric toothbrushes where because Hey am designed to be used the bathroom in the vicinity of sinks and we -, it is not safe to provide a conventional electrical connection. US6,356,049, US6301,128, (JS6,118,249, To all describe various homes of inductive chargers. Obese

( inductive type chargers, however, use traditional transformer designs with windings wound around fe-mte magnetic cores as shown in Sigh. The main magnetic flux between the primary winding and secondary winding has to go through the magnetic core materials. Other contactless chargers proposed also use magnetic cores as the main 5 tncture for the coupled transformer voidings.

A contactless chance using A single primary printed winding without any EMI shielding has been proposed by Choi et al in "A new contactless battery charger for portable telecommunications/computing electronics', ICCE Inrematioral Conference on Consumer Electronics 2001 Pages 58-59. However, the snagnetic flux distribution of a 10 single spiral winding has a major problem of non-uniform magnetic flux distribution.

As illustrated father below, the magnitude of the snagnctic field in the centre of the

core of a spiral winding is highest and decreases from the centre. This means that if the portable electronic device is not placed properly in the central region, the charging effect is not effective in this non- uniform field distribution. Furthermore. without

15 proper EMI shielding undesirable induced currents may flow in other metallic park of the portable electronic equipment.

SUMMARY OF THE lNVION

According to the present invention there is provided a battery charge system 20 comprising a charging module composing a primary charging circuit and being formed with a planar charging surface adapted to receive an electronic device to be charged, wherein said primary charging circuit Includes the primary winding of a transformer, said primly winding being substantially parallel to said planar charging surface, wherein said primary wading is provided with electramagnet:ic shielding on the side of

(am\ said winding opposite firm said planar charging surface, and wherein said electronic device is formed with a secondary winding.

In a preferred embodiment the primary winding is Conned on a planar printed circuit board s Preferably the magnetic flux generated by the primary winding is substantially unifonn over at least n major part of the planar charging surface. In this way the precise position and orientation of Me electronic device on the charging surface is not critical.

To achieve dhis the charging m odule may comprise a plurality of primary windings, which may preferably be disposed in a regular array.

1 0 In a preferred em bodim ant the prim ary winding is provided with electromagnetic shielding on the side of said winding opposite fron, said planar charm ng surface. T his shielding may include a sheet of ferrite material, and more preferably also m ay farther include a sheet of conductive material such as copper or aluminium 15 It is an advantage of the present invention that in preferred embodiments the planar charging surface may be large enough to receive no or more electronic devices, and the primary charging circuit is adapted to charge two or more devices simultaneously. In this way it is possible to charge more than one device simultaneously. For example the planar charging surface may be divided into a 20 plurality of charging regions, which regions may be derqDed by providing a plurality of primary transformer windings arranged in a regular array and connecting Me windings in groups to define said charging regions, A further advantage of the present invention is that it enables the possibility of allowing a device to move over the charging surface while bug charged at We same time. This possibility is particularly usefi1 to a device 25 which is designed to be moved such as a wireless computer mouse

' 4 (A Viewed from another aspect the present invention provides a battery charging system composing a charinlj; module comprising a primary charging circuit Ed being formed with a charging surface for receiving an electronic device to be charged, wherein said charging module comprises a plurality of transformer primary windings 5 arranged in a regular array.

In addition to the battery charging system, the invention also extends to a battery powered portable electronic device composing a rechargeable battery, and wherein the device includes a planar secondary winding for receiving electrical energy from a battery charger, and electromagnetic shielding between the winding and the 10 major electronic components of said device.

Preferably the shielding comprises a sheet calf ferrite matenal and a sheet of conductive natenal such as copper.

Preferably the winding is formed integrally with a back cover of said device.

An important aspect of the present invention.is that it provides a battery 15 charging system that employs a localised charging concept. In particular, when there is an array of primary coils, it will be understood Hat energy is only transferred from those primary coils that arc adjacent the secondary coil located in the device being charged. In other words, when a device is placed on a planar charging surface that is greater in size than the device, energy is only transferred from that part of she planar 20 charging surface that is directly beneath the device, and possibly also immediately adjacent areas that are still able to couple to the secondary coil.

BREF DESCRIPTION OF THE r)RAUGS

Some embodiments of the invention will now be described by way of example 2S and with reference to the accompanying drawings, in wbich:

l' s : Fg.l is a schematic view of a conventional prior art battery charger with direct

electrical connection.

Fig.2 is Schematic view of conventional magnetic core-basód ansfomer as used in prior art inductive battery charger systems,

5 Fig 3 is a schematic view of a planar transformer with shielding, Figs. 4(a)-(c) are (a) a perspective view of a battery charger system according to an embodiment of the present invention, (b) a view similar to (a) but showing the structure of the prunary charging system' and (c) a view similar to (a) and (b) but showing the top cover removed for clarity, 10 Fig,s.(a) (b) show the structure of the primary charger with the top cover removed for clarity, and in Fig.S(a) with the structure shown in mcp]cded view, Figs.6(a) & (b) show (a) single spiral PCB winding, and (b) the measured magnetic field distribution of single spiral winding,

Figs.7(a) & (b) illustrate the use of a magnetic core to control magnetic field

I 5 distribution, Fig.8 shows an embodiment of the invention in which plurality of pnmory windings are arranged in an array stuchlre, Figs.9(a) (b) shows (a) a 4 x 4 primary winding array, and (b) the resulting magnetic field distribution,

20 Figs.lO(a)-(c) illustrate an embodiment of the invention in which primary windings are arranged in groups with Fig, 1 o(c) Showing the equivalent circuit, Fight shows an example of the back cover of electronic device designed to be recharged using an embodiment of the present invention, Figs 12(a)-(d) show exploded views of the back cover of Fig.11,

-. Figs.13(a) & (b) show views of a watch that may be recharged in accordance with an embodiment of the invention, Fig, 14 shows a charging module in acc ordance with an alternative embodiment of the invention, 5 Fig.15 shows a first layer of a 4xS \vinding array for use in a multilayer embodiment, Fig.16 shoves a second layer of a 3x4 winding array for use in conjunction with the layer of Fig.15 In a mulli-layer embodiment, Fig.17 shows the layers of Fig.lS and Fig 16 in the tvvo-1ayer structure, 10 Fig.18 is simplified version of Fig.15, Fig.l9 is a simplified version of Fig.16, Fig.20 is a simplified version of Fig, 17, Fig.2 1 is a plot showing the smoothing effect of the two-layer structure, Fsg.22 shows a hexagonal spiral winding, 15 Pig.23 is a simplified form of Pig.22, Fig. 24 shows a single-layer of hexagonal spiral windinl3s, Fig.25 shows two adjacent hexagonal spiral windings, Fig.26 shows Me mmf tisibution of the adjacent windings of Fig.2S, Fig27 shoves three adjacent hexagonal spiral windings and the peaks and 20 minima ofthe flux distribution, Fig.28 chows two overlapped layers of hexagonal spiral windings, Fig.29 sloops the location of We peak flux in Me structure of Fig.28, Fig.30 corresponds to Fig.29 but also shows the location ofthe Box Miranda, Fig 31 shows an embodiment of Me invention formed with thee overlapped 25 layers,

Fig.32 corresponds to Fig.3 I but shows the location of the flux peaks, Fig.33 is a plot showing the uniformity of Me flux distribution alone a line, Fig.34 shows a square spiral winding;, Fig 35 is a simplified version of Fig.34, 5 Fig.36 shows a first layer of square spiral Grindings, Pig.37 corresponds to Fig.36 but shows the location of the flux maxima and . momma, Fig.38 shows two overlapped layers of square spiral windings including the location ofthe flux maxima and mining, 10 Fig.39 shows three overlapped layers of square spiral windings including the location of the flux tnaxima and minima, and Fig.40 chow' four overlapped layers of equarc spiral windings including Me location of the flux maxima and minima.

I 5 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be degesibed in respect of a preferred embodiment in the form of an inductive battery charger for portable electronic equipment such as mobile phones,}handheld computers and personal digital assistants (PDA), and devices such as a wireless computer mouse.

20 Referring firstly to Pig.4, me inductive charger system comprises two modules, a power delivering charger module that contain' the primary circuit of a planar isolation transfonner and a secondary CiTCUit that is located in the portable el=nic equipment to be charged. In this embodiment of the invention, Tic charger circuit is located within a housing 1 Mat is formed with a flat charging surface 2. The secondary 25 circuit is fonned in the portable equipment to be clanged (in this example a mobile

l' 8 (A phone 3) and the equipment is formed with at least one planar surface. As will be seen Mom the following description the equipment is Charged simply by placing the

equipment on the surface so that the planar surface on the equipment is brought into contact with the flat charging surface 2. It is a particularly preferred aspect of the 5 present invention that the equipment to be charged does not have to be positioned on the charging surface in any special orientation. Furthennore. in preferred embodiments of the invention two or more mobile devices may be charged simultaneously on the same charging surface, anchor a device that is designed to be moved (such as a wireless computer mouse) can be charged while being moved over the charging surface (which 10 could be integrated into a computer mouse pad). It will also be seen from the following descnption that the energy transfer is "localized" in the sense that energy is only trsniefced from the charging surface to the device from that pan of me charging surface that is directly beneath the device (and possibly to a lesser extent regions adjacent thereto).

15 Referring in particular to Fig.(b) the primary charging module comprises a printed circuit board conned with at roast one spiral conductive track formed thereon as a primary winding. It will be understood, however, that the primary winding need not necessarily be formed on a PCB and could be formed separately. Preferably, as will be described fiuther below, shore are in fact a plurality of such spiral tracks disposed in 20 an array as shown in Fig.4(c). Beneath the PCB 4 (is the side of the PCB away from the charging surface) is prowded EMI shicldug comprising firstly a fenite sheet s adjacent the PCB 4, and then a conductive sheet 6 which in this example may be a copper sheet.

Bencad1 the copper sheet 6 may be provided any suitable foyers of substrate material 7, eg a plastics material. Above the PCB 4 may be provided a shoes of insulating material 25 8 which fonns the charging surface. Preferably Be PCB 4, the 1SMI shielding sheets 5,6,

An' the substrate 7 and the insulating cover sheet 8 may also be generally the same size and shape, for example rectangular, so as to fond the primary charging module with the charging surface being large enough to accommodate at least one, and more preferably two or more, devices to be charged. Figs 5(a) and (b) also show the structure of the 5 changing module without the cover sheet and without any devices to be charged thereon for the sake of clarity.

As shown in Fig.4, the primary transfonner circuit module transmits electrical energy at high fiequency through a flat charging surface that contains the primary transformer windings. The secondary winding is also planar and is located in the 10 portable electronic equipment and couples this energy, and a rectifier within the portable equipment rectifies the high-6equency secondary AC voltage into a DC voltage for charging the betray inside the portable equipment either directly or via a charging circuit. The rectified DC voltage is applied to the battery via mechanical contacts provided in an integrated back cover as will be described farther below. No 15 physical electrical connection between the primary charger circuit and the portable electronic equipment is needed.

The primary charger circuit has (1) switched mode power electronic circuit, (2) tlte primary side of a planar transfomcr that consists of a group of primary windings connected in series or in parallel or a combination of both, (3) an EMI shield and (4) a 20 flat interface surface on which one or more portable electronic devices can be placed and charged imulneously. The schematic of the primary charger system is shown in Fig.5 without the insulating coves.

The battery charging system can be powered by AC or DC power sources. If the power supply is the AC mains, the switched mode power electronic circuit should 25 perfonn a low-equency (50 or 60Hz) AC to DC power conversion and tiled DC to

high-frequency (typically in the range Dom 20kHz to lOMHz) AC power conversion.

This high-hequency AC voltage will feed the primary planar windings of me prunary chance circuit. If the power supply is a battery (e.g. a car battery), the switched mode power supply should perform a DC to highhequency AC power conversion. The high 5 frequency voltage is fed to the primary windings of the planet transformer.

Preferably, the charger should be able to charge one or more than one items of portable electronic equipment at the same time. In order to achieve such a function, the AC magnetic flux experienced by each item of portable equipment placed on the charging surface should be as even as possible. A standard planar spiral winding as 10 shown in Fig.6(a) is not suitable to meet this requirement because its flux distribution is not uniform as shown in Fig.6(b) when the winding is excited by an AC povver source.

The reason for such non-uniform magnetic flux distubulion is that the number of turns in the central region of the single spiral winding is largest. As the magnitude of the magnetic flux and the magnetomotive force (mmf) is proportional to the product of the 15 number of turn and the current in the winding, the magnetic flux is highest in the centre of the Grinding.

One method to ensure unifonn magnetic flux or mmf distribution is to use a concentric primal winding with a planar magnetic core as shown in Fig. 7(a). Lois magnetic corcbased approach allows the magnetic flux to concentrate inside the core 20 and typical magnetic flux distribution is shown in Fig.7(b). En general, the net charging interface surface of the primary charger should be larger Han the total area of the portable electronic equipment.

order to ensure that more than one item of portable electronic equipment can be placed on the flat charging surface alla charged simultaneously, a second and more 25 preferred method proposed is to ensure that the magnetic flux distribution experienced

by each it's of portable electronic equipment is as ifom as possible, This method can be realized by using a "ditubuted" primary planar tranEforner winding aney structure as shown in Fig.8. This planar winding array consists of many printed spiral windings forrood on the PCB. These pouted spiral windings can be hexagonal, circular, 5 square or rectangular spirals, and can be connected in series, in parallel or a combination of both to the hi-frequency AC voltage generated in the power supply in the primary charger circuit. The array should comprises relatively closely spaced coils so as to be able to generate the required near-uniform magnetic flux distribution, as an array of widely spaced apart coils may not generate such a near-uniform field.

10 Fig.9(a) shows a practical example with the transformer winding array comcoted in series so that all the fluxes created in the windings point the same direction. Fig.9(b) show the measured flux distribution of one planar transformer when the windings in the transformer array are connected in series. This measurement confirms the near uniform magnetic flux distribution of the aTay structure. Comparison 15 of Fig.6(b) and Fig.9(b) confirms the improvement of the unifonn magnetic Geld distribution using the former array stmcnre In addition, this transformer may structure provides for Me possibility of multiple primary transformer windings being provided for localized charging as will now be explained.

The primary ansfonner windings can also take We form of a combination of 20 series and parallel connections if desired. Such an arrangement allows the charging surface to be divided into various charging regions to cater for different sizes of Me secondary windings inside Me portable electronic equipment. Fig.10(a) illustrates this localized charging zone principle. Assume Mat the transformer array is divided into 4 zones (A, El, C, and D). The transformer windings within each zone are connected in 25 series to forth one primary winding group win the distributed magnetic flux feature.

l V 12 There will be four primary windings in the equivalent circuit as shown in Fig. 1 0(c). If the portable electronic equipment is placed on Zones A and B as shown in Fig.10(b), the equivalent clocical circuit is shown in Fig.10(c3. Only the parallel primary transformer winding groups for Zones A and B are loaded because they can sense a S nearby secondary Ending circuit in He portable electronic equipment, Therefore, they will generate magnetic flux in Zones A and B. Primary transformer windings C and P are not loaded because they have no secondary transformer circuit close to them and their equivalent secondary circuits are simply an opencircuit (Fig.10(c)). As a result, power transfer between the primary charger circuit and the secondary windings inside 10 the portable electronic equipment takes place basically through the coupled regions (areas) of the charging interface surface covered by the portable electronic equipment.

The non-covered area of He charging surface will transfer virtually no energy, This special design avoids unnecessary electromagnetic interference. A Aver advantage of this localized energy transfer concept, is that it enables a movable device (such as a 15 wireless computer mouse) to be continually charged as it moves over the charging surface. In the case of a wireless computer mouse, for example, the primary charging circuit could be integrated into a mousepad and the mouse may be charged as it moves over the mousepad.

The back cover of Me podable electronic equipment a detachable beck cover 20 that covers the batterer and which may be removed when the battery is replaced. In preferred anbodimerts of Tic present invention, this back cover has a built-in SCCD plan transformer winding, a diode rectifier circuit and preferably a thin EMI shield as shown in Fig.12(b) & (c). When the back cover side of the portable equipment is placed near the flat charging surface of We primary charger circuit, this 25 secondary winding couples the energy from the nearby primary transformer winding or

windings. The rectifier circuit rectifies the coupled AC voltage into a DC voltage for charging the battery. This rectifier circuit SO prevents the baked Mom discharging into the secondary winding. In order to avoid induced circuit from circulating in over metal parts inside podable electronic circuit, it is preferable to include a Din EMI 5 shield as part of the integrated back cover structure as shown in Fig.12. This EM1 shield can be a thin piece of femte material (such as a flexible ferrite sheet developed by Siemens) or ferrite sheets, or more preferably a combination of a fertile sheet and then a thin Upper sheet It will thus be seen that, at least in its preferred forms, the present invention 10 provides a new planar inductive battery charger for portable electronic equipment such as mobile phones, handheld computers, personal data assistant (PDA) and eleconie watches, and wireless computer mice. Ibe intuctivc charger system consists of two modules, including (1) a power delivenug charger circuit that contains Me prnmary circuit of a planar isolation transformer and a flat charging surface and (2) a separate 15 secondary transformer circuit tlmt consists of a punted winding, a rectifier and preferably a thin EMI shield and which is located in the portable eloconic equipment to be charged.

An advantage of the present invention, at least in prefe'Ted fortes, is that the primary charger circuit system has the primary side of a planar hansfonner and a flat 20 interface surface on which one or more portable electronic devices can be placed and charged dmulteneoualy. The secondary circuit can be integrated into the back cover of the portable eloconic device or separately placed inside the electronic device. The invention also cxtesds to a back cover design with an in-built secondary circuit for the portable equipment The secondary winding of the planet transformer can be EMI 25 shielded and integrated into the back cover adjacent to the battery in the portable

(A electronic device. As long as the back cover sides of the portable electronic device are placed on the charger surface, one or more portable electronic devices can be charged simultaneously, regardless of their orientations.

Figs.13(a) and (b) show how an embodiment of the invention may be used to 5 recharge a watch battery. A watch is Conned with a basic watch mechanism 20, which is powered by a rechargeable battery 21. The watch mechanism is shielded Bom electrical interference in the charging process by an EMI shield consisting of, for example, a copper sheet 22 and a fertile sheet 23 (with the copper sheet closer to the watch mechanism than the femte sheet). The other side of the EMI shield is provided a 10 planar careless trarssformer secondary winding 24 Conned with electrical contacts for connection to the battery 21 and with a rectifier circuit to prevent dish of the battery. Finally, the watch structure is completed by the provision of a planar back cover 25 Conned of non-metallic matenal. It will be understood that the watch battery may be recharged by placing the watch on tle charging surface of a battery charging 15 system as described in the above embodiments such that the back cover 25 lies flat on the planar charging surface. Electrical cocrgy is then coupled Mom the pnmay winding() in the battery charging module to the secondary winding in the watch and then to the rechargeable bancry.

In We embodunents described above the charging module is formed as a single 20 integral unit (as shown for example in Figs.4 and S). However, in some situations it y be desirable to separate the electronic charging circuit Mom the planar charging surface. This possibility is shown in Fig. 14 in which the electronic charging circuit 20 is coTmcted by a cable 21 to the charging surface 22 The charging surface 22 includes an insulating top cover, the planar primer,, windings printed on a PCB, and a bottom 25 EMI shield formed of femte and a conductive sheet such as copper. This embodcat

go has the advantage that the charging surface is relatively thin, and therefore may be useful for example when the device to be charged iG a wirele" computer mouse because the charging surface can double as a mousepad as well as a charging surface In the embodiments descnbed above a single layer of transformer arrays is 5 prodded. However, in order to generate a more unifonn magnetic field distribution,

multi-layer transformer arrays can be used. The following embodiments describe how multiple layers of transformer arrays may be used that can provide a very uniform magnetic field distubuton on the charging surface.

Fig.15 shows a 4xS primary planar transformer winding away which consists of 10 square-sprial Grinding patterns. This can be fabricated on one layer of the printed circuit board structure. It should be noted that, for an individual winding patter' in the array, the magnitude of Tic magnetic flux is highest in the center of Me spiral winding. 1 he magnitude of the magnetic flux is smallest in He small gap between adjacent winding patterns. IS A second layer with a 3:c4 transformer winding array is shown in Fig.16. lThe individual Ending patterns in both IBYOr8 are identical. As shown in Fig. 17, by halving the two layers of arrays arranged in such a manner that the center (region of maximum magnetic flux magnitude) of a winding pattern on one layer is placed on the gap (region of minimum magnetic flux magnitude) between adjacent winding patterns on the other 20 layer, the variation of Me magnetic field magnitude can be minimized and tle magnetic

flux magnitude can therefore be made as even as possible OVCT Me overlapped surface.

The essence of the multi-layer transformer arrays is to have a displacement bcve̳n We individual winding patterns of the two layers so that the regions of We maximum magnetic field magnitude of one layer is "evened out's by the regions of the minimum

25 magic field magnitude.

l (a In order to examine the 'uniform magnetic field magnitude' feature of the

proposed overlapped multi-layer trenaformer arrayed this 'magnitude smoothing' concept is illustrated in simplified diagrams in Fig.18 to 20. Fig.18 is a simplified version of Fig.lS. Each solid square in Fig.ll represents a square-spiral winding 5 pattern in the first layer (Fig.lS). Fig.l9 is a simplified version of the Fig.16. Bach dotted square represents a square-spiral windup pattern in the second layer (Fig.16).

The simplified version of the multi-layer atTay structure is shown in Fig. 20. From Fig.20, it can be seen that the overlapped array structure (withcorrect displacement between the two layers) divides each square-spiral winding pattern into four smaller 10 sub-regions. The important feature is that the four sub-regions are identical in terms of winding structure Despite that fact that the distribution of the magnetic field magnitude

on the surface of each individual square-spiral winding is not uniform, the distribution of the resultant magnitude field magnitude on the surface of each sub-region is more or

less identical because of the overlapped multi-layer winding structure. The concept of 15 the generating uniforsn magnetic field natude over the chaTaine surface is illustrated

in Fit.21.

this cxanple, a multi-layer transfonner winding array structure that can provide a uniform magnetic field magnitude distribution is descnbed. This example is

based on square-sp*al winding patterns. In principle, winding patterns of other shapes 20 can also be applied as long as the resultant magnetic field magnitude dissolution is as

uniform as possible.

The use of two layers of transformer arrays can reduce the Radon in the magnetic flux over the charging surface. However, Mere may still be some vexations and We use of a three or fou* layer structure may provide a still more umfom flux 25 distribution as described in Me following embodiments.

it' The following embodiment is a structure comprising three layers of planar winding Stays. Tbic PCB winding structure can onorate magnstomotive force (mm,l) of substartially even magnitude over the charging surface Each winding array consists of a plurality spiral windings each of which are of an hexagonal shape. A spiral 5 winding arranged in a hexagonal shape is shown in Fig.22. For simplicity, it will be represented as a hexagon as shown in Fig.23. A plurality of hexagonal spiral windings can be arranged as an array as shown in Fig.24. These windings can be connected in parallel, in seines or a combination of both to the electronic driving circuit. If a current passes through each spiral winding pattern, a magnetomotive force (maid' which is 10 equal to the product of the number of turns (Al) and current (0 (i.e. N7), is generated.

Fig.2S shows two spiral winding pattems adjacent to each other and the perunit mmf plot over the distance (dotted line) cut be linearized as shown in Fig 26. It can be seen that the mmidistribution over the distance is not uniform. The maximum mn7foccurs in the center of the hexagonal pattern and the minimum mmf occurs in the edge of the 15 pattern.

Fig.27 shows Tree adjacent windings. The maximum mmiregion iB labelled by a symbol 'P' (which stands for Peak imp). The minimum nnfregion at the junction of nvo patterns is labeled as 'V' (which stands for Valley of the mmf distnution) order to generate a uniform man distribution over the planar charging surface, two 20 more layers of PCB winding arrays should be added. This principle is explained firstly by adding a second layer of PCB winding array to the first one as shown in Fig.28. The second layer is placed on Me first one in such a way that the peak mmipositions (P) of the patters of one layer me placed directly over the valley positions (V) of the patters in the over layer. Fig.29 highlights the peak positions of We patterns Mat are directly 25 over the valicy positions of Me other layer for the two overlapped PCB layers in Fig.28.

It can be observed from Fig.29. however, that the use of two layers of PCB winding arrays, while presenting an improvement over a single layer, does not offer the optimal solution for generating unicorns mmf over the inductive charging surface. For each hexagonal pattern in the 2-layer structure, the peak positions occupy the central 5 position and three (out of six) vertices of each hexagon. The remaining three vertices are valley positions (V) that need to be filled by a third layer of PCB winding arrays.

These valley positions are shown in Fig.30 as empty squares Careful examination of Fig.30 shows that there are six peals positions (P) surrounding each valley position. Therefore, a third layer of a hexagonal PCB winding 10 array can be used to fill up all these remaining valley positions. By placing the central positions (peals miff positions) of the hexagonal winding pattem6 of the third layer of the PCB windlug array over the remaining valley positions of the two-layer structure, an optimal three-layer structure is formed as sbovn in Fig.31 Fig.32 highlights the peals mmf positions of the three-layer structure. It can be observed that all central 15 positions and vertices of all hexagonal patterns have peak off: In order to óonfirrn that the mmf over the surfeóe has uni form mmf distribution, any distance between any two adjacent peak mmi positions can be considered as illustrated in Fig.33. If the winding patterns are excited in the same manner and polarity so that the mmf generated by each layer of the winding array are always in the same 20 direction at any moment, the resultant mmf is simply the sum of the mmf generated by each layer. The dotted line in Fig.33 shows that the resultant mmf over the distance between any hvo adjacent peak positions in Fig.33 is equal to 1.D per unit. This confirms that the proposed three-layer PCB winding array skuct.ure can be used to generate highly unifonn mmJ over the inductive charging surface. When used as a 25 contactless, inductive charging surface, this unifonn mmf distribution feature ensures

(A that, for a given airgap, a secondary PCB coupling winding can always couple the same amount of magnetic flux regardless of the position of the secondary (coupling) PCB on the inductive charging surface. In addition, the voltage induced in the secondary winding would be the same over the inductive charging surface.

5 another embodiment, the three-layer PCB winding array structure can be constructed as a four-layer PCB, with one of Me four layer" acconunodatins the retum paths of the spiral windings to the electronic diving circuit A further embodiment is based again on square spiral winding pattems. In this embodiment four layers of square-spiral winding arrays are used to generate highly 10 unifonn mmfever the PCB surface. As in the hexagonal embodiment described above, for convenience of illustration each square.spiral winding pattern (E:ia.34) is simplified as a square symbol (Fig.35) us the following desenption.

Fig.36 shows the first layer of the square-spiral PCB winding array. The mmf in the central region of each square pattern is highest. These regions are highlighted as 15 'Peak' or (P) in Fig.37. The regions of the minimum mmf(i.e. the valleys) occurs along the edges of the square patterns. These regions are highlighted with tots (a) in Fig.37.

order to reduce the mmf ripples on the surface, the peak (P) positions of a second layer of square-spiral PCB winding array can placed over some of the valley positions) as shown in Fig.3B. When a third layer of squamspiral PCH winding 20 array is added to the structure in Fig.38, the resultant layout is Mown ir' Fig.39. It can nova be observed that one more layer of the squarspirl PCB windings is needed to fill up all the valleys with peaks as shown in Pig.40.

The present invention, at least in preferred forms, provides a new charging system allows more than one piece of equipment to be charged simultaneously. and

regardless of their orientations on the charging surface, and allows a movable device to be charged while it moves over the charging surface.

Claims

t COWS 1. A battery charger system comprising a charging module

comprising a primary charging circuit arid being Conned with a planar charging surface adapted to receive an electronic device to be charged, wherein said primary charging 5 circuit includes the primary winding of a transformer, said primary winding being substantially parallel to said planar charging surface, wherein said primary winding is provided with electromagnetic shielding on flee side of said winding opposite Mom said planar charging surface, and wherein said electronic device is formed with secondary winding.

2. A battery charger system as claimed in claim 1 wherein said transfomcr primary winding is Conned on a printed circuit board.

3. A battery charging system as claimed in claim I wherein We magnetic flux 15 generated by said primary winding is substantially unifonn over at least a major pm of said planar charging surface.

4. A battery charging system as claimed in claim 1 wherein said charging module comprises a plurality of primary windings.

s. A battery charging system as claimed in claim 4 wherein said primary windings are disposed in a regular array.

(A 6. A battery charging system as claimed in claim 4 wherein said primary windings are formed in a multi-layer structure comprising at Icast two layers arid with each said layer including an array of primary windings.

5 7. A battery charging system as claimed in claim 6 Wherein the array of a first said layer is offset relative to the anay of a second said layer whereby regions of said first layer generating maximum magnetic flux coincide with regions of said second layer that generate minimum magnetic flux.

10 8. A battery charging system as claimed in claim 6 composing three layers of hexagonal vvinding.

9. A battery charging system as claimed in claim 6 comprising four layers of square windings.

10. A battery charging system as clanncd In claim 5 wherein said pnmaIy windings are hexagonal, circular, rectangular, square or polygonal in shape.

11. A battery charger system as claimed in claim 1 wherein said shielding includes 20 a sheet of femte material.

12. A battery charging system as claimed in claim I 1 wherein said shielding furler includes a second sheet of conductive material.

( 13 battery charging system as claimed in claim wherein said planar charging surface is large enough to receive two or more cloctronic devices, and wherein said primary charring circuit is adapted to charge two or more devices simultaneously. s 14. A battery charging system as claimed in claiml3 wherein said planar charging surface is divided into a plurality of charging regions.

15. A battery charging system as cloned in claim 14 wherein said primary I O charging circuit comprises a plurality of primary transformer windings arranged in a regular array and wherein said windings are connected in groups to dcfinc said charging regions 16. A battery charging system as claimed in claim 1 wherein said primary charging IS circuit comprises an array of primary windings, and wherein when device is placed on said charging surface charging energy is Transferred lo said device hum only those primary windings closely adjacent to said device.

11. A battery charging system as claimed in claim 1 wherein said planar charging 20 surface is large enough to enable a said device to be moved over said charging surface while being charged.

18. battery charging system comprising a charging module comprising a primary charging circuit and being fanned win a charging surface for receiving an

me' electronic device tc, be charged' wherein said charging module comprises a plurality of transfonner primary windings arranged in a regular array.

19. A battery charging system as claimed in claim 18 wherein when an electronic 5 device to be charged is placed on said charging surface charging energy is transferred to said device fiom only those primary Shadings closely adjacent to said device.

00. A battery charging system as claimed in claim 18 wherein said transformer I O primary windings are connected to each other in series and/or in parallel, 21. A baker, charging system as claimed in claim 18 wherein said primary transfonner windings are planar and substantially parallel to a planar charging surface. Liz. A battery charging system as claimed in claim 21 wherein said primary windings are fanned in at least two planes, each said plane including an array of said windings.

20 23. A battery charging system as claimed in claim 22 wherein the array of a first said plane is offset relative to the array of a second said plane whereby regions of said first array Mat generate maximum magnetic flux coincide win regions of said second array Mat generate minimum magnetic flux.

24. A battery charging system as claimed in cluing 22 composing three layers of hexagonal Windings.

25. A battery charging system as claimed in claim 22 comprising four layers of 5 square windings.

26. A batterer charging system as claimed in claim 21 wherein said primary windings are fanned on a pnuted circuit board.

10 27. A battery charging system as claimed in claim 21 wherein electromagnetic shielding is provided on Tic side of said primary windings opposite from said planar charging surface.

28 A battery charging system as claimed in claim 27 wherein said shielding 15 composes a sheet of famte matonal.

29. A battery charging system as claimed in claim 28 wherein said shielding further composes a second sheet of conductive material.

20 30. A battery charging system as claimed in claim 18 wherein said charging surface is large enough to allow two or more devices to be charged thereon simultaneously.

1 ' 31. A battery charging system as claimed in claim 18 wherein said charging surface is large enough to allow a device to be moved over the charging surface while being charged.

5 32. A battery powered portable electronic device comprising a rechargeable bakery, and wherein said device includes a planar secondary winding for receiving electrical energy from a battery charger, and electromagnetic shielding between said winding and the major electronic components of said device.

10 33 An electronic device as clanged in claim 32 wherein said shielding comprises a sheet of ferrite material and sheet of conductive matenal.

34. An electronic device as c]airned in claim 32 wherein said winding is conned integrally with a back cover of said device.