PATENT DOCUMENT

Publication Number: US-10593468-B2
Application Number: US-201816134812-A
Country: US
Kind Code: B2

Title: Inductive power transfer assembly

Abstract:
An inductive power transfer assembly comprising a magnetic core having a base portion, a first limb, and a second limb, wherein the first limb and the second limb extend, in a direction, from a surface of the base portion a first power transfer coil and a second power transfer coil, wherein the first power transfer coil is wound about the first limb, and wherein the second power transfer coil is wound about the second limb; and inverter circuitry connected to the first power transfer coil and the second power transfer coil, wherein the inverter circuitry, during operation, causes the first power transfer coil and the second power transfer coil to generate flux having opposing polarity.

Claims:
What is claimed is: 
     
       1. An inductive power transfer assembly comprising:
 a magnetic core having a base portion, a first limb, and a second limb, wherein the first limb and the second limb extend, in a direction, from a surface of the base portion; 
 a first power transfer coil and a second power transfer coil, wherein the first power transfer coil is wound about the first limb, and wherein the second power transfer coil is wound about the second limb; and 
 inverter circuitry connected to the first power transfer coil and the second power transfer coil, wherein the inverter circuitry, during operation, causes the first power transfer coil and the second power transfer coil to generate flux having opposing polarity. 
 
     
     
       2. The inductive power transfer assembly of  claim 1 , wherein the flux generated by the first power transfer coil and the second power transfer coil during operation produces a directional flux field, wherein the directional flux field is directed away from the base portion, along the direction of extension of the first limb and the second limb. 
     
     
       3. The inductive power transfer assembly of  claim 1 , wherein the first limb extends from the surface of the base portion along an axis, and wherein the first power transfer coil is wound about the limb circumferentially along the axis. 
     
     
       4. The inductive power transfer assembly of  claim 3 , wherein the axis is normal to the surface of the base portion of the magnetic core. 
     
     
       5. The inductive power transfer assembly of  claim 4 , wherein the first limb and second limb extend from a flat portion of the base portion of the magnetic core. 
     
     
       6. The inductive power transfer assembly of  claim 1 , wherein the first limb and the second limb have the same size and shape. 
     
     
       7. The inductive power transfer assembly in  claim 1  wherein the coils are arranged to couple to an inductive power receiver. 
     
     
       8. The inductive power transfer assembly in  claim 1  wherein the base having a width wider that a width of the coils. 
     
     
       9. The inductive power transfer assembly in  claim 8  wherein the base is 1/%, 5% or 10% wider that the coils. 
     
     
       10. The inductive power transfer assembly in  claim 1  wherein the limbs being substantially inset from the base. 
     
     
       11. The inductive power transfer assembly in  claim 1  wherein the base is between 0.4 mm and 2 mm in height, the limbs are between 1.8 mm and 5 mm in height. 
     
     
       12. The inductive power transfer assembly in  claim 1  wherein the coils include between 15 and 30 turns and are 2 layers. 
     
     
       13. The inductive power transfer assembly in  claim 1  further comprising a partial copper electromagnetic shield or copper plating. 
     
     
       14. The inductive power transmitter in  claim 1  wherein the core is a moulded ferrite core. 
     
     
       15. An inductive power transfer assembly comprising:
 a magnetic core having a base portion, a first limb and a second limb, wherein the first limb and the second limb extend, in a direction, from a surface of the base portion; 
 a first power transfer coil and a second power transfer coil, wherein the first power transfer coil is wound about the first limb, and wherein the second power transfer coil is wound about the second limb; and 
 a transverse power transfer coil, wherein the transverse power transfer coil is wound about the base portion. 
 
     
     
       16. The inductive power transfer assembly in  claim 15  further comprising a converter connected to the two power receiving coils and receiving current from each coil with opposing polarity. 
     
     
       17. The inductive power transfer assembly of  claim 16 , wherein the current received from each coil is derived from flux received in the respective limb about which the coil is wound. 
     
     
       18. The inductive power transfer assembly in  claim 15  wherein the two power transfer coils are arranged to couple to a first type of inductive power transmitter and the transverse power transfer coil is arranged to couple to a second type of inductive power transmitter. 
     
     
       19. The inductive power transfer assembly in  claim 18  wherein the base being substantially similar in length to a base of the first type of inductive power transmitter. 
     
     
       20. The inductive power transfer assembly in  claim 15  wherein the core further comprising a central limb. 
     
     
       21. The inductive power transfer assembly in  claim 20  wherein the transverse power transfer coil is provided around the central limb and the base. 
     
     
       22. The inductive power transfer assembly in  claim 15  wherein the base is between 1-50, 2-30, or 3-10 times as long as it is wide. 
     
     
       23. The inductive power transfer assembly in  claim 15  mounted within an associated wirelessly rechargeable stylus. 
     
     
       24. The inductive power transfer assembly in  claim 23  wherein the assembly is mounted within a compartment in the stylus and the assembly further comprising a partial copper electromagnetic shield in the compartment or copper plating of the compartment or the stylus. 
     
     
       25. The inductive power transfer assembly in  claim 15  wherein the limbs are each between 5-45%, 25-30% of the length of the base. 
     
     
       26. The inductive power transfer assembly in  claim 15  wherein a space between the limbs is between 5-60%, 10-50% or 20-40% of the length of the base. 
     
     
       27. The inductive power transfer assembly in  claim 15  wherein the base is between 1.1 mm and 2 mm in height, the limbs are between 1.8 mm and 5 mm in height. 
     
     
       28. The inductive power transfer assembly in  claim 15  wherein the coils include between 20 and 40 turns and are 3 layers. 
     
     
       29. The inductive power transfer assembly in  claim 15  wherein the core is a moulded ferrite core. 
     
     
       30. The inductive power transfer assembly in  claim 15  wherein a winding ratio between each of the first and second power transfer coils and the transverse power transfer coil is between 1:10 and 3:1, between 1:2 and 3:2, between 5:8 and 7:5. 
     
     
       31. An inductive power transfer system comprising:
 an inductive power transmitter assembly and an inductive power receiver assembly, the inductive power transmitter assembly comprising: 
 a magnetic core having a base portion, a first limb, and a second limb, wherein the first limb and the second limb extend, in a direction, from a surface of the base portion; 
 a first power transfer coil and a second power transfer coil, wherein the first power transfer coil is wound about the first limb, and wherein the second power transfer coil is wound about the second limb; and 
 inverter circuitry connected to the first power transfer coil and the second power transfer coil, wherein the inverter circuitry, during operation, causes the first power transfer coil and the second power transfer coil to generate flux having opposing polarity, 
 the inductive power receiver assembly comprising: 
 a magnetic core having a base portion, a first limb and a second limb, wherein the first limb and the second limb extend, in a direction, from a surface of the base portion; 
 a first power transfer coil and a second power transfer coil, wherein the first power transfer coil is wound about the first limb, and wherein the second power transfer coil is wound about the second limb; and 
 a transverse power transfer coil, wherein the transfer power transfer coil is wound about the base portion, and 
 wherein the first limb and second limb of the transmitter and the first limb and second limb of the receiver are configured to be aligned with each other in use. 
 
     
     
       32. The inductive power transfer system in  claim 31 , wherein at least a portion of each of the first and second limbs of the transmitter assembly have a greater length along a long axis of the transmitter core than the length of each of the first and second limbs of the receiver assembly along a long axis of the receiver core.

Description:
This application claims the benefit of provisional patent application No. 62/653,406, filed Apr. 5, 2018, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to wireless systems, and, more particularly, to systems in which devices are wirelessly charged. 
     BACKGROUND 
     In a wireless charging system, a wireless power transmitting device such as a device with a charging surface or zone wirelessly transmits power to a portable electronic device. The portable electronic device receives the wirelessly transmitted power and uses this power to charge an internal battery or to power the device. 
     SUMMARY 
     In some situations, achieving good coupling between inductive power transmitters and receivers can be difficult. Poor coupling can result in slow charging of power receivers, high power consumption in transmitters, high leakage of charging fields and energy inefficiency. 
     In the system, a wireless power transmitting device transmits wireless power signals to a wireless power receiving device. The wireless power transmitting device has an inverter that supplies signals to an output circuit that includes wireless power transmitting coils. The wireless power receiving device includes wireless power receiving coils. 
     The wireless power transmitting device includes a magnetic core that has a base portion with first and second limbs extending from the base portion. The coils of the wireless power transmitting device are wound about the limbs of the magnetic core of the wireless power transmitting device. 
     The wireless power receiving device includes a magnetic core that has a base portion with first and second limbs extending from the base portion. The coils of the wireless power receiving device are wound about the limbs of the magnetic core of the wireless power receiving device. Magnetic cores can assist in directing and concentrating magnetic flux produced by the transmitting device and received by the receiving device. 
     The wireless power receiving device can also include a transverse coil wound about the base portion of the magnetic core of the wireless power receiving device. The transverse coil can improve reception of wireless power signals. For example, the transverse coil can receive power from wireless power fields oriented transverse to the direction of extension of the limbs of the magnetic core. In some situations, the wireless power receiving device could be placed on a charging mat or similar assembly with a charging surface. The wireless power receiving device may be arranged such that the transverse coil is aligned substantially parallel to the charging surface when the receiving device is placed on the charging surface in order to receive power in the transverse coil. In some situations, the wireless power receiving device could be configured to couple to a corresponding transmitter in a preferred position/orientation during charging. In these situations, the transverse coil may improve coupling in the case that the receiving device is not optimally positioned or oriented with respect to the transmitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless charging system in accordance with some embodiments. 
         FIG. 2  is a schematic diagram of an illustrative inductive power transfer assembly with a core, coils and in inverter in accordance with an embodiment. 
         FIG. 3  is a side view of an illustrative inductive power transmitting device showing the core, base, first and second limbs, first and second coils in accordance with an embodiment. 
         FIG. 4  is an end view of an illustrative inductive power transmitting device showing the base, one of the limbs and one of the coils in accordance with an embodiment. 
         FIG. 5  is a top view of an illustrative inductive power transmitting device showing the core, limbs and coils. 
         FIG. 6  is a side view of an illustrative inductive power transmitting device including a third limb and a transverse coil. 
         FIG. 7  is a schematic view of an illustrative inductive power transmitter circuit. 
         FIG. 8 . is a schematic diagram of an illustrative inductive power transfer assembly with a core and coils in accordance with an embodiment. 
         FIG. 9  is a side view of an illustrative inductive power receiving device with a base, first and second limbs, first and second coils and a transverse coil in accordance with an embodiment. 
         FIG. 10  is an end view of an illustrative inductive power receiving device showing the base, one of the limbs and one of the first and second coils and the transverse coil in accordance with an embodiment. 
         FIG. 11  is a top view of an illustrative inductive power receiving device showing the core, limbs and coils. 
         FIG. 12  is a schematic view of an illustrative inductive power receiver circuit. 
         FIG. 13  is a side view of an illustrative inductive power transfer system showing an illustrative inductive power transmitting assembly and an illustrative inductive power receiving assembly in accordance with an embodiment. 
         FIG. 14  is a schematic diagram of an illustrative tablet computer including an inductive power receiving device in accordance with an embodiment. 
         FIG. 15  is a schematic diagram of an illustrative mobile phone including an inductive power receiving device in accordance with an embodiment. 
         FIG. 16  is a schematic diagram of an illustrative electronic accessory including an inductive power receiving device in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system has a wireless power transmitting device that transmits power wirelessly to a wireless power receiving device. The wireless power transmitting device is a device such as a wireless charging mat, wireless charging puck, wireless charging stand, wireless charging table, or other wireless power transmitting equipment. The wireless power transmitting device may be a stand-alone device or built into other electronic devices such as a laptop or tablet computer, cellular telephone or other electronic device. The wireless power transmitting device has one or more coils that are used in transmitting wireless power to one or more wireless power receiving coils in the wireless power receiving device. The wireless power receiving device is a device such as a cellular telephone, watch, media player, tablet computer, pair of earbuds, remote control, laptop computer, electronic pencil or stylus, other portable electronic device, or other wireless power receiving equipment. 
     During operation, the wireless power transmitting device supplies alternating-current signals to one or more wireless power transmitting coils. This causes the coils to transmit alternating-current electromagnetic signals (sometimes referred to as wireless power signals) to one or more corresponding coils in the wireless power receiving device. Rectifier circuitry in the wireless power receiving device converts received wireless power signals into direct-current (DC) power for powering the wireless power receiving device. 
     Wireless power transmitting and receiving devices can be designed to cooperate specifically with each other. For example, the size, shape, number, dimensions and configuration of coils of one or both of the devices may be selected based on the other device. Magnetic elements may also be included in the transmitting and/or receiving device, and the size, shape, number, dimensions and configuration of the magnetic elements may be selected based on the other device. 
     In some cases, wireless power transmitting and receiving devices can be designed to be closely coupled to each other. Typically, this is achieved by arranging the coils of the transmitting and receiving devices such that they are aligned with and close to each other in use. Systems in which the transmitting and receiving devices can be closely coupled to each other in use are sometimes referred to as inductive power transfer systems. Transmitting and receiving devices that can be closely coupled to receiving devices can be referred to as inductive power transfer devices. 
     Wireless power transmitting and receiving devices and transmitters can also be designed to cooperate with each other in particular orientations, positions or other spatial relationships. For example, some receiving devices may have a preferred position or orientation with respect to a transmitting device. This preferred position or orientation may allow for good power transfer, minimum leakage of the charging field and other advantageous effects. The transmitting and/or receiving devices may have visual markings to indicate where or in what orientation to place the receiving device, engaging elements to hold the receiving device in a particular position or orientation, magnetic couplings or other biasing elements to urge the receiving device towards a particular position or orientation, or other arrangements. 
     Wireless power transmitting and receiving devices can also be used with other devices without being specifically designed to cooperate with them. For example, a wireless power transmitting device can operate with many different types of receiving devices having different coil arrangements, different (or no) magnetic elements, sizes, shapes and other characteristics. A wireless power receiving device can operate with many different types of transmitting devices having different coil arrangements, different (or no) magnetic elements, sizes, shapes and other characteristics. 
     Wireless power transmitting and receiving devices can also be used in various orientations, positions or other spatial relationships. For example, wireless power transmitting or receiving devices may be provided without visual markings, engaging elements, magnetic couplings or other biasing elements, or other arrangements. Alternatively, transmitting or receiving devices may have these arrangements but still operate in various other orientations and positions. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , a wireless power system  8  includes a wireless power transmitting device  12  and one or more wireless power receiving devices such as wireless power receiving device  10 . Device  12  may be a stand-alone device such as a wireless charging mat, may be built into furniture, laptop or tablet computers, cellular telephones or other electronic devices, or may be other wireless charging equipment. Device  10  is a portable electronic device such as a wristwatch, a cellular telephone, a tablet computer, an electronic pencil or stylus, or other electronic equipment. Illustrative configurations in which device  12  is a tablet computer or similar electronic device and in which device  10  is an electronic accessory that couples with the tablet computer or similar electronic device during wireless power transfer operations may sometimes be described herein as examples. Illustrative configurations in which device  12  is a mat or other equipment that forms a wireless charging surface and in which device  10  is a portable electronic device or electronic accessory that rests on the wireless charging surface during wireless power transfer operations may also sometimes be described herein as examples. 
     During operation of system  8 , a user places one or more devices  10  on or near the charging region of device  12 . Power transmitting device  12  is coupled to a source of alternating-current voltage such as alternating-current power source  50  (e.g., a wall outlet that supplies line power or other source of mains electricity), has a battery such as battery  38  for supplying power, and/or is coupled to another source of power. A power converter such as AC-DC power converter  40  can be included to convert power from a mains power source or other AC power source into DC power that is used to power control circuitry  42  and other circuitry in device  12 . During operation, control circuitry  42  uses wireless power transmitting circuitry  34  and one or more coils  36  coupled to circuitry  34  to transmit alternating-current electromagnetic signals  48  to device  10  and thereby convey wireless power to wireless power receiving circuitry  46  of device  10 . 
     Power transmitting circuitry  34  has switching circuitry (e.g., transistors in an inverter circuit) that are turned on and off based on control signals provided by control circuitry  42  to create AC current signals through appropriate coils  36 . As the AC currents pass through a coil  36  that is being driven by the switching circuitry, a time varying electromagnetic field (wireless power signals  48 ) or “flux” is produced, that is received by one or more corresponding coils  14  electrically connected to wireless power receiving circuitry  46  in receiving device  10 . If the time varying electromagnetic field is magnetically coupled to coil  14 , an AC voltage is induced and a corresponding AC currents flows in coil  14 . Rectifier circuitry in circuitry  46  can convert the induced AC voltage in the one or more coils  14  into a DC voltage signals for powering device  10 . The DC voltages are used in powering components in device  10  such as display  52 , touch sensor components and other sensors  54  (e.g., accelerometers, force sensors, temperature sensors, light sensors, pressure sensors, gas sensors, moisture sensors, magnetic sensors, etc.), wireless communications circuits  56  for communicating wirelessly with control circuitry  42  of device  12  and/or other equipment, audio components, and other components (e.g., input-output devices  22  and/or control circuitry  20 ) and/or are used in charging an internal battery in device  10  such as battery  18 , or to charge subsequent devices, either wired or wirelessly. 
     Devices  12  and  10  include control circuitry  42  and  20 . Control circuitry  42  and  20  may include storage and processing circuitry such as analogue circuitry, microprocessors, power management units, baseband processors, digital signal processors, field-programmable gate arrays, microcontrollers, application-specific integrated circuits with processing circuits and/or any combination thereof. Control circuitry  42  and  20  is configured to execute instructions for implementing desired control and communications features in system  8 . For example, control circuitry  42  and/or  20  may be used in determining power transmission levels, processing sensor data, processing user input, processing other information such as information on wireless coupling efficiency from transmitting circuitry  34 , processing information from receiving circuitry  46 , using information from circuitry  34  and/or  46  such as signal measurements on output circuitry in circuitry  34  and other information from circuitry  34  and/or  46  to determine when to start and stop wireless charging operations, adjusting charging parameters such as charging frequencies, coil assignments in a multi-coil array, and wireless power transmission levels, and performing other control functions. Control circuitry  42  and/or  20  may be configured to perform these operations using hardware (e.g., dedicated hardware or circuitry) and/or software (e.g., code that runs on the hardware of system  8 ). Software code for performing these operations is stored on non-transitory computer readable storage media (e.g. tangible computer readable storage media). The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, other computer readable media, or combinations of these computer readable media or other storage. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  42  and/or  20 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, or other processing circuitry. 
     Device  12  and/or device  10  may communicate wirelessly. Devices  10  and  12  may, for example, have wireless transceiver circuitry in control circuitry  42  and  20  (and/or wireless communications circuitry such as circuitry  56  of  FIG. 1 ) that allows wireless transmission of signals between devices  10  and  12  (e.g., using antennas that are separate from coils  36  and  14  to transmit and receive unidirectional or bidirectional wireless signals, using coils  36  and  14  to transmit and receive unidirectional or bidirectional wireless signals, etc.). For example device  12  and/or device  10  may communicate using in-band communications injected or combined into the wireless power signals  48  such as proposed in the Wireless Power Consortium Qi specification 1.1, which is incorporated herein by reference. Alternatively a separate Bluetooth®, RFID, NFC, Zigbee, Wifi RF or other communication system may be employed. 
     An illustrative inductive power transfer assembly  110  is shown in  FIG. 2-5 . As shown in  FIG. 2-5 , the inductive power transfer assembly  110  includes a magnetic core having a base  114 , a first limb  116  and a second limb  118 . The base has a front surface  113  and a back surface  115 . The inductive power transfer assembly also includes a first coil  120  wound about the first limb  116  and a second coil  122  wound about the second limb  118 . The coils  120 ,  122  are connected to inverter circuitry  124 . The inverter circuitry  124  can drive the coils  120 ,  122  to generate flux. During operation, the first coil  120  and second coil  122  can be driven to generate flux having opposing polarity. 
     Various types of inverter circuitry can be used to drive the coils  120 ,  122 . For example, a simple chopper circuit can be used to provided alternating current signals to the coils  120 ,  122 . In such a circuit, a switch or combination of switches can alternately connect a DC supply voltage to different sides of a coil to provide an alternating voltage across, and current through, the coil. Capacitive or inductive elements can be used to smooth the output waveform. 
     In some examples, the inverter circuitry  124  may be a push-pull inverter in which the coils are connected in series and switches operate to provide an alternating voltage across, and current through, the coils. In some examples, the inverter may be a resonant inverter that includes one or more capacitive elements that form(s) a resonant circuit with one or both of the coils  120 ,  122  and optionally other inductive elements. Resonant inverters can include actively controlled switches that are controlled based on the resonant frequency of the inverter circuit. Resonant inverters can be soft switched, using zero voltage or zero current switched, hard switched or a variation of either. 
     One illustrative inverter is shown in the inductive power transmitter circuit  200  of  FIG. 6 . In this example, the inverter  124  is an H-bridge inverter comprised of a DC source and switches  204 ,  206 ,  208 ,  210 . The switches  204 ,  206 ,  208 ,  210  are alternately operated in pairs to provide alternating current to the inductive power transfer assembly  110 . In particular, switches  204  and  210  may be closed simultaneously, while switches  206 ,  208  are open, to provide current flow in a first direction through the transfer assembly  110 . Then switches  206 ,  208  can be closed simultaneously, while switches  204 ,  210  are open, to provide current flow the opposite direction through the transfer assembly  110 . In this example, the inductive power transfer assembly is connected in series with a capacitor  202 . The combination of the coils  120 ,  122  of the transfer assembly  110  and the capacitor  202  creates a resonant circuit. The switches  204 ,  206 ,  208 ,  210  may be operated at or near the resonant frequency of the resonant circuit or with some other relationship to the resonant frequency. 
     It will be appreciated that there are many types of inverter suitable for supplying alternating current to transmitter coils that would be suitable for use with the present power transmitting device. 
     The inverter circuitry  124  drives the coils  120 ,  122  to generate flux having opposed polarity. In some examples, the coils  120 ,  122  are electrically connected in series but have opposed magnetic axes. For example, a single length of conductor can be wound into two coils having opposite winding directions—i.e. such that current flowing clockwise through one flows counter-clockwise through the other—such that the magnetic axes of the coils  120 ,  122  are oriented to oppose each other. The inverter circuitry  124  is arranged to supply the length of conductor with electric current, which will cause the coils  120 ,  122  to generate flux having opposed polarity. The polarity of the flux generated by one coil may have an orientation substantially 180 degrees different from the polarity of flux generated by the other coil. 
     The coils  120 ,  124  may each be wound about the respective limbs  116 ,  118  circumferentially along the axis of the respective limb—i.e. in the direction that the limb extends from the front surface  113  of the base  114 . 
     In some examples, the coils  120 ,  122  are electrically connected in parallel but have opposed magnetic axes. For example, two lengths of conductor can be wound into two coils having opposite winding directions—i.e. such that a current will flow clockwise through one and counter-clockwise through the other—such that the magnetic poles of the coils  120 ,  122  are oriented oppositely. Or alternatively the coils may be connected with the opposite ends connected to the inverter output terminals respectively, to drive the current in the opposite direction. The inverter circuitry  124  is arranged to supply the lengths of conductor with electric currents of similar phase, which will cause the coils  120 ,  122  to generate flux having opposed polarity. 
     In some examples, the coils  120 ,  122  are wound with separate conductors wound in the same winding direction—i.e. both clockwise or counter-clockwise. The inverter circuitry  124  is arranged to supply the coils  120 ,  122  with electric currents of opposing phase, which will cause the coils  120 ,  122  to generate flux having opposed polarity. 
     In some examples, the inverter circuitry  124  can include a separate inverter for each coil. The separate inverters may independently control the phase of current supplied to the coils  120 ,  122  to operate with various different phase relationships. This allows the inverter circuitry  124  to independently control the polarity of flux generated by the coils  120 ,  122  to operate the transmitting device  110  with various different flux polarity relationships. 
     The transfer assembly  110  may also be provided with phase-delay components to provide a controllable phase difference between current in the first coil  120  and current in the second coil  122 . In these examples, a single inverter may drive both coils  120 ,  122  while still providing for independent control of current in the coils  120 ,  122  to operate the transmitting device with various different flux polarity relationships. The phase delay components may include analog components such as capacitors and inductors or digital components such as integrated circuits or microcontrollers. 
     It will be appreciated that the coils may be wound from a single-strand conductor, a multiple strand conductor having multiple wires connected in parallel, braided wire, Litz wire, a conductive ink or conductive trace such as multilayer tracks on a printed circuit board, or other conductive elements suitable for forming coils. 
     In some examples, the coils  120 ,  122  are comprised of between 10 and 50 turns, between 15 and 30 turns, or approximately 20 turns. In some examples, the coils are comprised of between 1 and 5 layers, between 1 and 3 layers, or 2 layers. In some examples, the coils have the same number of turns as each other. In some examples, the coils have the same number of windings as each other. In some examples, the coils are comprised of the same number of layers as each other. 
     In some examples, the coils  120 ,  122  extend in the width direction between 1 mm and 10 mm, between 2 mm and 7 mm, between 2.7 mm and 5 mm, or approximately 3.2 mm. 
     In some examples, the coils each extend in the length direction between 3 mm and 20 mm, between 5 mm and 15 mm, between 6.5 mm and 11 mm, or approximately 7.5 mm. 
     In some examples, the coils each extend in the height direction between 0.5 mm and 4 mm, between 1 mm and 3 mm, between 1.6 mm and 2.5 mm, or approximately 2.1 mm. 
     In some examples, the inductive power transfer assembly  110  may include a transverse coil  119  wound about at least the base  114  of the core  112 . The transverse coil  119  can be driven to produce a magnetic flux through the core in the same direction as the flux produced by the first and second coils. This may result in a greater total flux being produced by the assembly  110 . The assembly  110  may include a third limb  117  onto which the transverse coil  119  is wound. The third limb  117  can be located centrally between the first and second limbs  116 ,  118 . The third limb  117  can be located on the base  114  of the core  112 . The third limb  117  also extends away from the front surface  113  of the core  112 . The third limb  117  may be substantially parallel to one or both of the first and second limbs  116 ,  118 . 
     In some examples, the transverse coil  119  is comprised of between 18 and 60 turns, between 24 and 45 turns, between 30 and 38 turns, or approximately 33 turns. In some examples, the transverse coil is comprised of between 1 and 7 layers, between 2 and 5 layers, or 3 layers. The transverse coil may be between 1 mm and 20 mm in length, between 2 mm and 10 mm in length, between 3 mm and 5 mm in length, or approximately 3.6 mm in length. 
     The transverse coil  119  can be a solenoid coil in which the length of the coil is greater than the diameter of the coil. 
     Each coil may be wound onto carrier, such as a bobbin or former, before being placed on the core  114 . Alternatively, each coil may be wound directly to the core  112 . 
     The first and second coils  120 ,  122  may be arranged to couple to coils of an inductive power receiving device. The coils  120 ,  122  may be located, oriented or sized to couple to coils of the inductive power receiving device. For example, the coils  120 ,  122  can be wound about limbs  116 ,  118  that are spaced a distance  127  apart to at least partially align with limbs and coils of an inductive power receiving device that power is to be transmitted to. This may enable the flux generated by the transfer assembly coils  120 ,  122  to efficiently couple into the receiving device coils. 
     The limbs  116 ,  118  may be spaced apart in the length direction by a distance  127  that is less than the spacing of the limbs of an inductive power receiving device. The distance  127  may be between 1 mm and 6 mm, between 2 mm and 4.5 mm, between 2.6 mm and 3.5 mm, or approximately 2.9 mm. 
     The distance  127  between the first and second limbs  116 ,  118  has an effect on the coupling between the power transfer assembly  110  and an inductive power receiver. Smaller distances may result in higher maximum coupling (when the transfer assembly  110  and receiver are optimally aligned than larger distances. However, transfer assemblies with smaller distances between the first and second limbs may be more sensitive to misalignment, such that the amount of power transferred from the assembly  110  to a receiver decreases more quickly with increasing misalignment than it does for transfer assemblies with larger distances between limbs. 
     The distance  127  can be selected based on the degree of misalignment expected between the assembly  110  and an inductive power receiver in use. In some examples, a misalignment of approximately +/−2 mm along either or both of the length and width axes  250 ,  260  may be expected in use. 
     In some examples, the core  112  may not include first and second limbs or first and second coils. In these examples, the assembly  110  may include a substantially flat core  112  with a transverse coil wound about the core  112 . These assemblies may be easier to manufacture than assemblies with first and second limbs and first and second coils. 
     The base  114  of the magnetic core  112  can be elongate, having one long axis, the “length”  250 , and two shorter orthogonal axes, the “width”  260  and “height”  270 . The length  250  and width  260  lie on a major “front” surface  113  from which the limbs  116 ,  118  extend. The limbs  116 ,  118  can be spaced from each other along the length axis  250 . 
     The length of the core  112  may be between 5 mm and 50 mm, between 10 mm and 35 mm, between 15 mm and 25 mm, or approximately 18 mm. The width of the core  112  may be between 1 mm and 10 mm, between 2 mm and 7 mm, between 2.8 mm and 5 mm, or approximately 3.4 mm. The height of the core  112  may be between 0.8 mm and 30 mm, between 1.5 mm and 15 mm, between 2.2 mm and 8 mm, or approximately 2.55 mm. 
     The extension of the first and second limbs  116 ,  118  along the length axis  250  may be between 1 mm and 20 mm, between 4.5 mm and 14 mm, between 6 mm and 10 mm, or approximately 7 mm. The extension of the first and second limbs  116 ,  118  along the width axis  260  may be between 1 mm and 10 mm, between 2 mm and 7 mm, between 2.5 mm and 5 mm, or approximately 3 mm. The extension of the first and second limbs  116 ,  118  along the height axis  270  may be between 0.5 mm and 20 mm, between 1.2 mm and 10 mm, between 1.8 mm and 5 mm, or approximately 2 mm. 
     The length of the base  114  may be between 5 mm and 50 mm, between 10 mm and 35 mm, between 15 mm and 25 mm, or approximately 18 mm. The width of the base  114  may be between 1 mm and 10 mm, between 2 mm and 7 mm, between 2.8 mm and 5 mm, or approximately 3.4 mm. The height of the base  112  may be between 0.1 mm and 10 mm, between 0.3 mm and 5 mm, between 0.4 mm and 2 mm, or approximately 0.5 mm. 
     The ratio of the extension along the length axis of the base  114  to either of the first and second limbs  116 ,  118  may be between 3:1 and 5:2, or approximately 18:7. 
     The inductive power assembly core  112  may be the same length as the core of an inductive power receiving device. The inductive power assembly core  112  may be longer than the core of an inductive power receiving device. 
     The first and second limbs  116 ,  118  may be inset from the perimeter of the base  114 . This is shown in  FIG. 3-5 . In the side view of  FIG. 3 , the first and second limbs are inset from the perimeter of the base in the length direction as indicated at  128   a . In the end view of  FIG. 4 , the first and second limbs are inset from the perimeter of the base in the width direction  260  as indicated at  128   b . The top view of  FIG. 5  shows the insets  128   a ,  128   b  of the limbs  116 ,  118  in both the width  260  and length  250  directions. The limbs may be inset by the same amount. Alternatively, the inset in one direction may be greater than the inset in the other direction. 
     The insets  128   a ,  128   b  may be such that the base extends further in the width and/or length directions than the first and second limbs  116 ,  118  by 1%, 5% or 10%. In some examples, the insets may each be between 0 mm and 10 mm, between 0.3 mm and 6 mm, between 0.6 and 3 mm, or approximately 0.75 mm. 
     The inset of the limbs reduces the overall length and width of the assembly when the coils are wound onto the limbs and can reduce fringing of the magnetic field to the sides and back  115  of the transfer assembly. 
     The coils  120 ,  122  may be wound onto the first and second limbs  116 ,  118  such that the coils  120 ,  122  are inset from the perimeter of the base  114 . This is shown in  FIG. 3-5 . In the side view of  FIG. 3 , the first and second coils are inset from the perimeter of the base in the length direction  250  as indicated at  129   a . In the end view of  FIG. 4 , the first and second coils are inset from the perimeter of the base in the width direction  260  as indicated at  129   b . The top view of  FIG. 5  shows the insets  129   a ,  129   b  of the coils  120 ,  122  in both the width  260  and length  250  directions. 
     The insets  129   a ,  129   b  of the coils described above mean that the base  114  of the core  112  extends out from the coils  120 ,  122  in the width  260  and length  250  directions, which may help reduce fringing of the magnetic field to the sides and back  115  of the transfer assembly  110  (i.e. in directions other than the direction of extension of the limbs). 
     The insets  129   a ,  129   b  may be such that the base extends further in the width and/or length directions than the first and second coils  120 ,  122  by 1%, 5% or 10%. In some examples, the insets may each be between 0 mm and 5 mm, between 0.1 mm and 3 mm, between 0.2 and 1 mm, or approximately 0.25 mm. 
     The first and second limbs  116 ,  118  may be the same size and shape as each other. 
     The first and second limbs  116 ,  118  may both extend in a direction substantially orthogonal to the planar surface at the front surface  113  of the base  114 , i.e. in the “height” direction  270 . For example the limbs  116 ,  118  may extend at an angle of up to 30 degrees to the normal of the planar front surface of the base; up to 15 degrees to the normal of the planar front surface of the base; up to 5 degrees to the normal of the planar front surface of the base; or approximately 0 degrees to the normal of the planar front surface of the base. 
     As shown in the top view of  FIG. 5 , the corners of the base may be rounded. This may provide improved guiding and shaping of the magnetic field and reduced leakage flux. It may also make the core easier to manufacture. 
     In use, the magnetic field generated by the coils  120 ,  122  can be guided by the first and second limbs  116 ,  118  of the core  112  and extend out from the distal end of one limb away from the base  114  of the core  112 . The field may extend into the distal end of the other limb toward the base  114 . It will be appreciated that the polarity of the magnetic field at a given time depends on the phase of current being supplied to the coils  120 ,  122 , and that when the direction of current changes, the direction of extension of the magnetic field will also change. 
     The relatively short extension of the core  112  in the height  270  and width  260  directions results in an elongate assembly  110  that can be installed in small compartments, housings or devices. 
     For example, the inductive power transfer assembly  110  may be installed in a laptop or tablet computer or mobile phone. These devices are typically thin and have limited space for components. This requires a transfer assembly to have small dimensions to fit within the device. 
     The core  112  is made of magnetically permeable material. For example, the core  112  may be ferrite, iron, mild steel, mu-metal or other magnetic materials. The core  112  may be a single piece or made from separate pieces. The core  112  may be moulded, sintered, formed from laminations or manufactured by other processes. 
     The inductive power transfer assembly  110  can be provided as part of wireless power charging device. For example, the transfer assembly can be provided in a charging base or stand, with which one or more devices to be charged wirelessly can engage. The wireless power charging device can take the form of a case, box or enclosure into which one or more devices to be charged can be placed. The wireless power charging device can take the form of an electronic device with built-in wireless charging capabilities that supplies wireless power in a charging region of the device. The wireless power charging device can take the form of a charging mat having a charging surface onto which one or more devices to be charged can be placed. 
     The inductive power transfer assembly  110  may be provided within an electronic device such as a laptop or tablet computer or a mobile phone. In one example, the device may have a charging zone for charging accessories such as styluses and electronic pencils. The inductive power transfer assembly can be arranged within the device to provide a charging field in the charging zone. The transfer assembly can be arranged such that limbs extend towards the exterior of the device at the charging zone. 
     The transfer assembly  110  may be provided in a compartment of the device and the compartment may have a partial electromagnetic shield or plating to shield electronics of the device from the charging field. The shield or plating may be made of copper or another suitable shielding material. The base of the core can extend across the width of the compartment. 
       FIG. 14  is an illustrative embodiment of a tablet computer  150  including an inductive power transfer assembly  110 . The inductive power transfer assembly  110  is shown within a compartment  152  of the tablet computer  150 . The compartment  152  or transfer assembly  110  includes a partial shield or plating  154 . The tablet computer  150  has a charging zone  156  at its surface in the region of the transfer assembly  110 . Devices to be charged can be placed in the charging zone  156  to receive power wirelessly from the inductive power transfer assembly  110 . The inductive power transfer assembly  110  may be located at the side of the tablet computer  150 . 
     The partial shield or plating  154  can act as a magnetic shield to reduce the amount of flux generated by the transfer assembly  110  reaching electronic components of the tablet computer  150 . 
     The tablet computer  150  can include magnets or other coupling means for retaining a wireless power receiving device placed at or near the charging zone  156 . For example, magnets could be provided as part of the transfer assembly  110 , within the compartment  152 , or in the region around the compartment  152 . 
       FIG. 15  is an illustrative embodiment of a mobile phone  170  including an inductive power transfer assembly  110 . The inductive power transfer assembly  110  is shown within a compartment  152  of the mobile phone  170 . The compartment  152  or transfer assembly  130  includes a partial shield or plating  154 . The mobile phone  170  has a charging zone  156  at its surface in the region of the transfer assembly  130 . Devices to be charged can be placed in the charging zone  156  to receive power wirelessly from the inductive power transfer assembly  110 . The inductive power transfer assembly  110  may be located at the side of the mobile phone  170 . 
     An illustrative inductive power transfer assembly  130  is shown in  FIG. 8-11 . As shown in  FIG. 8-11 , the inductive power transfer assembly  130  includes a magnetic core  132  having a base  134 , a first limb  136  and a second limb  138 . The base has a front surface  133  and a back surface  135 . The inductive power transfer assembly  130  also includes a first coil  140  wound about the first limb  136 , a second coil  142  wound about the second limb  138 , and a transverse coil  144  wound about the base  134 . 
     Each of the first and second coil  140 ,  142  may produce current from flux received in the limb on which it is wound. The transverse coil  144  may produce current from flux received in the base  134 . In some examples the transverse coil  144  may produce current from flux received in the base  134  and a third limb  137 . 
     The first and second power receiving coils  140 ,  142  may be arranged to couple to a first type of inductive power transmitting device and the transverse power receiving coil  144  may be arranged to couple to a second type of inductive power transmitter. For example, the first and second power receiving coils  140 ,  142  may be arranged to cooperate with corresponding limbs of an inductive power transmitter to form a low-reluctance loop out of the core  132  of the transfer assembly  130  and a corresponding core of the transmitter. The transverse coil  144  may be arranged to couple to a charging field at a charging surface of a charging mat. 
     The inductive power transfer assembly  130  may also include converter circuitry to convert the power received by one or more of the coils  140 ,  142  to a suitable form for a load or for powered components of the receiver device. For example, the converter may be a rectifier that converts alternating current (AC) power to direct current (DC) power. 
     The first and second coils  140 ,  142  may each be wound about the respective limb circumferentially along the axis of the limb—i.e. in the direction that the limb extends from the base  134 . 
     The first and second coils  140 ,  142  may be arranged to receive flux of opposing polarity and provide it to the converter. 
     In some examples, the first and second coils  140 ,  142  are electrically connected in series but have opposed magnetic axes. For example, a single length of conductor can be wound into two coils having opposite winding directions—i.e. such that current flowing clockwise through one flows counter-clockwise through the other—such that the magnetic axes of the coils  120 ,  122  are oriented to oppose each other. 
     In some examples, the first and second coils  140 ,  142  are electrically connected in parallel but have opposed magnetic axes. For example, two lengths of conductor can be wound into two coils having opposite winding directions—i.e. such that currents of similar phase will flow clockwise through one and counter-clockwise through the other—such that the magnetic axes of the coils  140 ,  142  are oriented to oppose each other. 
     In some examples, the coils are wound in the same direction—i.e. both clockwise or both counter-clockwise—such that the magnetic axes of the coils are oriented to not oppose each other. In this case, the converter circuitry may convert the power received from the coils  140 ,  142  separately. For example, the converter circuitry could include a separate rectifier for each of the first and second coils  140 ,  142 . 
     The transverse coil  144  could also be connected to the same rectifier as one or both of the first and second coils, or to a further rectifier. For example, the first, second and transverse coils could all be connected in series with each other and connected to the same rectifier. In another example, the first, second and transverse coils could each be connected to separate rectifiers. 
     The transfer assembly  130  may also be provided with phase-delay components to provide a control or reduce phase differences between current received in the coils  140 ,  142 ,  144 . In these examples, a single rectifier may be used to rectify current received in the coils  140 ,  142 ,  144  even if current is received with different polarity relationships. The phase delay components may include analog components such as capacitors and inductors or digital components such as integrated circuits or microcontrollers. 
       FIG. 11  is one example of a receiving device showing the electrical connection of the coils  140 ,  142  to wireless power receiving circuitry. In this example, the power receiving circuitry includes a rectifier  230 , a regulator  231  and a load  232 . 
     In one example configuration, the first and second coils  140 ,  142  are connected in series electrically. In this example, the coils are wound in opposing directions—i.e. clockwise and counter-clockwise—such that the first and second coils  140 ,  142  may receive flux of opposing polarity and produce current that is in phase. The transverse coil  144  is connected in parallel to the first and second coils  140 ,  142  and wound in a direction such that current produced by the transverse coil  144  will be in phase with the current produced by the first and second coils  140 ,  142 . 
     The first, second and transverse coils  140 ,  142 ,  144  are connected to rectifier  230  that converts the received alternating current into direct current. DC current from the rectifier is then provided to regulator  231  which controls the level of power provided to load  232 . 
     It will be appreciated that the conductor may be a single-strand conductor, a multiple strand conductor having multiple wires connected in parallel, braided wire such as Litz wire, a conductive ink or conductive trace, or other conductive element suitable for forming coils. 
     In some examples, the first and second coils  140 ,  142  are comprised of between 10 and 50 turns, between 20 and 40 turns, between 25 and 35 turns, or approximately 29 turns. In some examples, the first and second coils are comprised of between 1 and 7 layers, between 2 and 5 layers, or 3 layers. 
     In some examples, the first and second coils  140 ,  142  have the same number of turns as each other. 
     In some examples, the transverse coil  144  is comprised of between 18 and 100 turns, between 24 and 55 turns, between 30 and 38 turns, or approximately 33 turns. In some examples, the transverse coil is comprised of between 1 and 7 layers, between 2 and 5 layers, or 3 layers. The transverse coil may be between 1 mm and 20 mm in length, between 2 mm and 10 mm in length, between 3 mm and 5 mm in length, or approximately 3.6 mm in length. 
     The winding ratio between either or each of the first and second coils  140 ,  142  to the transverse coil  144  mat be between 1:10 and 3:1, between 1:2 and 3:2, between 5:8 and 7:5, or approximately 29:33. 
     The transverse coil  144  can be a solenoid coil in which the length of the coil is greater than the diameter of the coil. 
     In some examples, the first and second coils  140 ,  142  extend in the width direction  260  between 1 mm and 10 mm, between 2 mm and 7 mm, between 2.7 mm and 5 mm, or approximately 3.6 mm. 
     In some examples, the first and second coils  140 ,  142  each extend in the length direction  250  between 2 mm and 15 mm, between 4 mm and 11 mm, between 5.5 mm and 8 mm, or approximately 6.3 mm. 
     In some examples, the first and second coils  140 ,  142  each extend in the height direction  270  between 0.5 mm and 4 mm, between 0.9 mm and 3 mm, between 1.5 mm and 2.5 mm, or approximately 2 mm. 
     In some examples the transverse coil  144  extends in the length direction between 1 mm and 10 mm, between 2.5 mm and 7 mm, between 2.8 mm and 5 mm, or approximately 3.3 mm. 
     The ratio of the extension in the length direction of the transverse coil to either of the first and second coils may be between be 1:2 and 2:1, or approximately 11:21. 
     In some examples, the inductive power transfer assembly  130  may not include a transverse coil. 
     Each coil may be wound onto carrier, such as a bobbin or former, before being placed on the core  132 . Alternatively, each coil may be applied directly to the core  132 . 
     The coils  140 ,  142 ,  144  may be arranged to couple to coils of an inductive power transmitting device. The coils  140 ,  142 ,  144  may be located, oriented or sized to couple to coils of the inductive power transmitting device. For example, the coils  140 ,  142  can be wound about limbs  136 ,  138  that are spaced a distance  147  apart to at least partially align with limbs and coils of an inductive power transmitting device that power is to be received from. This may enable flux generated by coils of the power transmitting device to efficiently couple into coils of receiving assembly  130 . 
     The limbs  136 ,  138  may be spaced apart in the length direction by a distance  147  that is greater than the spacing of the limbs of an inductive power transmitting device. The distance  147  may be between 1.5 mm and 10 mm, between 3 mm and 7.5 mm, between 4 mm and 5.5 mm, or approximately 4.5 mm. 
     The distance  147  between the first and second limbs  136 ,  138  has an effect on the coupling between the power transfer assembly  130  and an inductive power transmitter. Smaller distances may result in higher maximum coupling (when the transfer assembly  130  and transmitter are optimally aligned) than larger distances. However, transfer assemblies with smaller distances between the first and second limbs may be more sensitive to misalignment, such that the amount of power transferred from a transmitter to the assembly decreases more quickly with increasing misalignment than it does for transfer assemblies with larger distances between limbs. 
     The distance  147  can be selected based at least partly on the degree of misalignment expected between the assembly  130  and an inductive power transmitter in use. In some examples, a misalignment of approximately +/−2 mm along either or both of the length and width axes  250 ,  260  may be expected in use. 
     The distance  147  can be selected based at least partly on properties of a charging device intended to provide power to the assembly  130 . For example, the distance can be selected based on the size or separation of transmitter coils of a charging mat. 
     The distance  147  can be between 5% and 60% of the length of the base, between 10% and 50% of the length of the base, between 20% and 40% of the length of the base, or approximately 30% of the length of the base. 
     In some examples, the core  132  may not include first and second limbs or first and second coils. In these examples, the assembly  130  includes a substantially flat core  132  with a transverse coil wound about the core  132 . These assemblies may be easier to manufacture than assemblies with first and second limbs and first and second coils. 
     The base  134  of the magnetic core  132  can be elongate, having one long axis, the “length”  250  and two shorter axes, the “width”  260  and “height”  270 . The length axis  250  and the width axis  260  of the base can form a substantially planar front surface  133  from which the first and second limbs  136 ,  138  extend. The first and second limbs  136 ,  138  can be spaced from each other along the length axis  250 . 
     The length of the core  132  may be between 5 mm and 50 mm, between 10 mm and 35 mm, between 15 mm and 25 mm, or approximately 17.5 mm. The width of the core may be between 1.2 mm and 12 mm, between 2.5 mm and 9 mm, between 3.8 mm and 6 mm, or approximately 4.5 mm. The height of the core may be between 1 mm and 10 mm, between 2 mm and 7 mm, between 2.8 mm and 5 mm, or approximately 3.4 mm. 
     The extension of the first and second limbs  136 ,  138  along the length axis  250  may be between 1 mm and 20 mm, between 3 mm and 12 mm, between 4.2 mm and 8 mm, or approximately 5 mm. The extension of the first and second limbs  116 ,  118  along the width axis  260  may be between 1 mm and 10 mm, between 2 mm and 7 mm, between 2.5 mm and 5 mm, or approximately 3.4 mm. The extension of the first and second limbs  116 ,  118  along the height axis  270  may be between 0.5 mm and 20 mm, between 1.2 mm and 10 mm, between 1.8 mm and 5 mm, or approximately 2 mm. 
     The length of the base  134  may be between 5 mm and 50 mm, between 10 mm and 35 mm, between 15 mm and 25 mm, or approximately 17.5 mm. The width of the base  134  may be between 1 mm and 15 mm, between 3 mm and 8 mm, between 4 mm and 6 mm, or approximately 4.5 mm. The height of the base  134  may be between 0.1 mm and 15 mm, between 0.8 mm and 5 mm, between 1.1 mm and 2 mm, or approximately 1.35 mm. 
     The base  134  may be between 1 and 50 times as long as it is wide, between 2 and 30 times as long as it is wide, between 3 and 10 times as long as it is wide, or approximately 4 times as long as it is wide. 
     The ratio of the extension along the length axis  250  of the base  134  to either of the first and second limbs  136 ,  138  may be between 20:1 and 20:9, 20:3 and 20:8, 20:5 and 20:6, or approximately 7:2. In other words, the limbs  136 ,  138  may each be between 5% and 45% the length of the base, between 15% and 40% the length of the base, between 25% and 30% the length of the base, or approximately 29% the length of the base. 
     The inductive power transfer assembly core  132  may be the same length as the core of the transmitting device. The inductive power transfer assembly core  132  may be shorter than the core of an inductive power transmitting device. 
     The first and second limbs  136 ,  138  may be inset from the perimeter of the planar surface of the base  134 . This is shown in  FIG. 8-10 . In the side view of  FIG. 8 , the first and second limbs are inset from the perimeter of the base  134  in the length direction  250  as indicated at  148   a . In the end view of  FIG. 9 , the first and second limbs are inset from the perimeter of the base  134  in the width direction  260  as indicated at  148   b . The top view of  FIG. 10  shows the insets  148   a ,  148   b  of the limbs  136 ,  138  in both the width  260  and length  250  directions. The limbs may be inset by the same amount. Alternatively, the inset in one direction may be greater than the inset in the other direction. 
     The insets  148   a ,  148   b  may be such that the base extends further in the width and/or length directions than the first and second limbs  136 ,  138  by 1%, 5% or 10%. In some examples, the insets may each be between 0 mm and 10 mm, between 0.3 mm and 6 mm, between 0.6 and 3 mm, or approximately 1.5 mm. 
     The inset of the limbs reduces the overall length and width of the assembly when the first and second coils are wound onto the limbs and can reduce fringing of the magnetic field to the sides and back  135  of the transfer assembly. 
     The first and second coils  140 ,  142  may be wound onto the first and second limbs  136 ,  138  such that the coils  140 ,  142  are inset from the perimeter of the planar surface of the base  134 . This is shown in  FIG. 8-10 . In the side view of  FIG. 8 , the first and second coils are inset from the perimeter of the base  134  in the length direction  250  as indicated at  149   a . In the end view of  FIG. 9 , the first and second coils are inset from the perimeter of the base  134  in the width direction  260  as indicated at  149   b . The top view of  FIG. 10  shows the insets  149   a ,  149   b  of the first and second coils  140 ,  142  in both the width  260  and length  250  directions. The coils may be inset by the same amount. Alternatively, the inset in one direction may be greater than the inset in the other direction. 
     The insets  149   a ,  149   b  may be such that the base extends further in the width and/or length directions than the first and second coils  140 ,  142  by 1%, 5% or 10%. In some examples, the insets may each be between 0 mm and 5 mm, between 0.2 mm and 3 mm, between 0.3 and 1 mm, or approximately 0.5 mm. 
     The insets  149   a ,  149   b  of the first and second coils described above mean that the base  134  of the core  132  extends out from the coils  140 ,  142  in the width  260  and length  250  directions, which may help reduce fringing of the magnetic field to the sides and back  135  of the transfer assembly  130 —i.e. in directions other than the direction of extension of the first and second limbs  136 ,  138 . 
     The first and second limbs  136 ,  138  may be the same size and shape as each other. 
     The base  134  of the core  132  may taper along the height direction  270  such that the back surface  135  of the base  134  extends further in the width direction  260  than the front surface  133  of the base  134  does. This can be seen in the end view of  FIG. 9 . This may allow the assembly to be located in small or irregular areas or compartments. For example, in a compartment with angled or rounded sides, such as in the interior of an electronic pencil or stylus, the tapered base  134  of the core allows it to be inserted deeper into a compartment such that the ends of the limbs  136 ,  138  are closer to the perimeter of the electronic pencil or stylus. 
     The first and second limbs  136 ,  138  of the transfer assembly  130  may each extend as far in the length direction  250  as each of the first and second limbs of a transmitting device. 
     The first and second limbs  136 ,  138  of the transfer assembly  130  may be shorter in the length direction  250  than each of the first and second limbs of a transmitting device. In other words, at least a portion of each of the first and second limbs, of the transmitting device have a greater length along the length axis  250  than each of the first and second limbs  136 ,  138  of the transfer assembly  130 . This provides more space between the first and second limbs for the transverse coil  144  to be located. 
     The first and second limbs  136 ,  138  may have a varying extension in the length direction  250 . For example, the limbs  136 ,  138  may have a shorter extension in the length direction  250  near the base  134  of the core than they do at their distal ends. This may provide more space between the first and second limbs  136 ,  138  for the transverse coil  144  to be located while still providing a relatively large surface facing a transmitter device. 
     The first and second limbs  136 ,  138  may both extend in a direction substantially orthogonal to the planar front surface  133  of the base  132 —i.e. in the “height” direction  270 . For example the limbs  136 ,  138  may extend at an angle of up to 30 degrees to the normal of the planar front surface  133  of the base  134 ; up to 15 degrees to the normal of the planar front surface  133  of the base  134 ; up to 5 degrees to the normal of the planar front surface  133  of the base  134 ; or approximately 0 degrees to the normal of the planar front surface  133  of the base  134 . 
     The relatively short extension of the core  132  in the height  270  and width  260  directions results in an elongate transfer assembly  130  that can be installed in small compartments, housings or devices. 
     For example, the transfer assembly  130  may be installed and mounted in an electronic accessory such as an electronic pencil or stylus. These accessories are elongate and narrow, which requires a receiving device to have a correspondingly small cross section to fit in the accessory. The transfer assembly may be installed or form part of other wireless power receiving devices. 
     The core  132  may also include a third limb  137  located centrally between the first and second limbs  136 ,  138 . The third limb  137  extends away from the front surface  133  of the core  132 . The third limb  137  may be substantially parallel to one or both of the first and second limbs  136 ,  138 . The transverse coil  144  may be wound about the third limb  137  and the base  134 . The third limb  137  may improve coupling of the assembly when the assembly is not optimally aligned with a transmitting device or when used on a charging surface of a charging mat. When the core includes a third limb, it may be advantageous to wind the first and second coils  140 ,  142  on a bobbin or former before applying them to the first and second limbs  136 ,  138  due to the space taken up by the third limb, which may make winding the coils directly onto the first and second limbs  136 ,  138  more difficult. 
     As shown in the top view of  FIG. 10 , the corners of the base  134  may be rounded. This may provide improved guiding and shaping of the magnetic field and reduce leakage flux. 
     The core  132  is made of magnetically permeable material. For example, the core  132  may be ferrite, iron, mild steel, mu-metal or other magnetic materials. The core  132  may be a single piece or made from separate pieces. The core may be moulded, sintered, laminated or manufactured by other processes. 
     The inductive power transfer assembly  130  may be provided within an electronic accessory such as an electronic pencil or stylus. In one example, the accessory or other receiving device can be configured to be placed in a charging zone of an electronic device such as a laptop or tablet computer or mobile phone. 
     In some cases, the accessory may be placed on a charging surface of a charging mat to receive power wirelessly. Generally, precise alignment of the transfer assembly with transmitting devices—e.g. coils or cores—of the charging mat is less likely to be achieved when placing a receiving device on a charging mat. This means that the first and second coils  140 ,  142  of the assembly  130  may not receive power as efficiently as they would if they were precisely aligned and/oriented with a transmitting device. 
     The transfer assembly  130  or electronic accessory or other wireless power receiving device may be configured to be retained in a particular position and/or orientation with respect to a wireless power transmitting device. For example, the assembly, accessory or device can include magnets for coupling with magnetic materials of the wireless power transmitting device in a particular position or orientation. The accessory or device could have a flat surface to provide the accessory or device with a preferred orientation when resting on a flat surface such as the exterior of an electronic device or the charging surface of a wireless power charging mat, or markings or other assistance to alignment. 
     The transfer assembly  130  may be provided in a compartment of the accessory or other device and the compartment may have a partial electromagnetic shield or plating to shield electronics of the accessory or other device from the charging field. The shield or plating may be made of copper or another suitable shielding material. The base  134  of the core  132  can extend across the width of the compartment. 
       FIG. 16  is an illustrative embodiment of an electronic accessory including an inductive power transfer assembly  130 . In this case, the electronic accessory is an electronic pencil or stylus  180 . The inductive power transfer assembly  130  is shown within a compartment  152  of the accessory. The compartment  152  or the transfer assembly includes a partial shield or plating  154 . The accessory can be placed in a charging zone of a wireless power transmitting device or on a charging surface of a wireless charging mat to receive power wirelessly via the inductive power transfer assembly  130 . 
     The inductive power transfer assemblies  110 ,  130  may be operated as an inductive power transmitting device  110  and an inductive power receiving device  130 , respectively. The inductive power transfer assemblies  110 ,  130  may be designed to couple to each other to provide good inductive coupling with low levels of leakage of magnetic flux. As shown in  FIG. 13 , the transmitting device  110  and receiving device  130  can be oriented face to face with the first and second limbs  116 ,  118  of the transmitting device  110  aligned with the first and second limbs  136 ,  138  of the receiving device  130 . The ends of the first and second limbs  116 ,  118  of the transmitting device  110  are also located proximate the ends of the first and second limbs  136 ,  138  of the receiving device  130 . In this arrangement, the cores  112 ,  132  of the transmitting device  110  and receiving device  130  provide a low-reluctance loop for the magnetic flux generated by the transmitter coils  120 ,  122 . 
     In use, the inverter  124  energizes the first and second coils  120 ,  122  of the transmitting device  110  to generate magnetic flux of opposing polarities. The flux path is directed outwards from a first limb (e.g.  116 ) of the transmitting device  110 , inwards to a first limb (e.g.  136 ) of the receiving device  130 , through the base  134  of the receiving device  130 , outwards from a second limb (e.g.  138 ) of the receiving device  130 , inwards to a second limb (e.g.  118 ) of the transmitting device  110  and through the base  114  of the transmitting device  110  back to the first limb  116  of the transmitting device. It will be appreciated that the direction of this flux path depends on the instantaneous phase of current through the coils of the transmitting device. 
     The alignment and close proximity of the ends of the first and second limbs  116 ,  118 ;  136 ,  138  of the transmitting device  110  and receiving device  130  provide good coupling of the magnetic flux generated by the coils  120 ,  122  of the transmitting device to the receiving device  130 . This allows the first, second and transverse coils  140 ,  142 ,  144  to efficiently receive power from the changing flux passing through the coils. 
     It will be appreciated that the system of  FIG. 13  can be comprised of any combination of the illustrative power transfer assemblies  110 ,  130  described herein. For example, the system could include a power transfer assembly  110  with or without a transverse coil  117  operating as a power transmitting device and a power transfer assembly  130  with or without a transverse coil  144  operating as a power receiving device. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination, and elements from one embodiment may be combined with others.

Metadata:
Filing Date: 20180918
Publication Date: 20200317
Grant Date: 20200317
Priority Date: 20180405
Inventors: CHEN, LIANG
REN, SAINING
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J7/0042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/0042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F27/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/346", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/346", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/0042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/346", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 68099026