PATENT DOCUMENT

Publication Number: US-10938251-B1
Application Number: US-202017016242-A
Country: US
Kind Code: B1

Title: Wireless power mode switching

Abstract:
A wireless power system may include an electronic device and a removable case. The electronic device and removable case may include wireless charging coils that are inductively coupled when the electronic device and the removable case are physically coupled. In a first mode, while the removable case is inductively coupled to the electronic device and the electronic device is not connected to a wired power source, a coil in the removable case transmits wireless power signals to the electronic device. In a second mode, while the removable case is inductively coupled to the electronic device and the electronic device is connected to a wired power source, the coil in the removable case receives wireless power signals from the electronic device. In a third mode, the removable case receives wireless power with a first coil and transmits wireless power to the electronic device with a second coil.

Claims:
What is claimed is: 
     
       1. An accessory for an electronic device, comprising:
 a first wireless charging coil; 
 a second wireless charging coil; and 
 control circuitry configured to:
 in a first mode, while the accessory is inductively coupled to the electronic device and the electronic device is not connected to a wired power source, transmit wireless power signals to the electronic device using the first wireless charging coil; 
 in a second mode, while the accessory is inductively coupled to the electronic device and while the electronic device is connected to a wired power source, receive wireless power signals from the electronic device using the first wireless charging coil; and 
 in a third mode, while the accessory is inductively coupled to both the electronic device and a power transmitting device, transmit wireless power signals to the electronic device using the first wireless charging coil while receiving wireless power signals using the second wireless charging coil. 
 
 
     
     
       2. The accessory of  claim 1 , further comprising:
 a battery that is interposed between the first and second wireless charging coils. 
 
     
     
       3. The accessory of  claim 2 , further comprising:
 rectifier circuitry that is configured to, in the second mode, convert the wireless power signals received at the first wireless charging coil into a direct current voltage and charge the battery using the direct current voltage. 
 
     
     
       4. The accessory of  claim 3 , wherein the rectifier circuitry is further configured to, in the third mode, convert the wireless power signals received at the second wireless charging coil into an additional direct current voltage and charge the battery using the additional direct current voltage. 
     
     
       5. The accessory of  claim 2 , wherein the accessory has first and second opposing planar surfaces, wherein the first wireless charging coil is positioned adjacent the first planar surface, and wherein the second wireless charging coil is positioned adjacent the second planar surface. 
     
     
       6. The accessory of  claim 5 , further comprising:
 at least one dielectric layer that forms the first and second planar surfaces, wherein the battery, the first wireless charging coil, and the second wireless charging coil are formed in the at least one dielectric layer. 
 
     
     
       7. The accessory of  claim 1 , wherein the first wireless charging coil is interposed between the second wireless charging coil and the electronic device when the accessory is inductively coupled to the electronic device. 
     
     
       8. The accessory of  claim 7 , wherein the second wireless charging coil is interposed between the first wireless charging coil and the power transmitting device while the accessory is inductively coupled to both the electronic device and a power transmitting device. 
     
     
       9. The accessory of  claim 1 , wherein the control circuitry is further configured to:
 in the first mode, place the second wireless charging coil on standby; and 
 in the second mode, place the second wireless charging coil on standby. 
 
     
     
       10. The accessory of  claim 1 , wherein the accessory is a case having a rear wall and peripheral sidewalls that define a recess configured to receive the electronic device. 
     
     
       11. The accessory of  claim 10 , wherein the first and second wireless charging coils are formed in the rear wall. 
     
     
       12. The accessory of  claim 1 , further comprising:
 a magnetic alignment structure that is configured to magnetically couple to an additional magnetic alignment structure in the electronic device. 
 
     
     
       13. The accessory of  claim 12 , wherein the first wireless charging coil is aligned with an additional wireless charging coil in the electronic device when the magnetic alignment structure is magnetically coupled to the additional magnetic alignment structure. 
     
     
       14. The accessory of  claim 1 , further comprising:
 a magnetic alignment structure that is configured to magnetically couple to an additional magnetic alignment structure in the power transmitting device. 
 
     
     
       15. The accessory of  claim 14 , wherein the second wireless charging coil is aligned with an additional wireless charging coil in the power transmitting device when the magnetic alignment structure is magnetically coupled to the additional magnetic alignment structure. 
     
     
       16. The accessory of  claim 1 , further comprising:
 inverter circuitry that is configured to apply drive signals to the first wireless charging coil to transmit the wireless power signals; and 
 rectifier circuitry that is configured to, in the third mode, relay the wireless power signals received at the second wireless charging coil to the inverter circuitry. 
 
     
     
       17. A non-transitory computer-readable storage medium storing one or more programs configured to be executed by one or more processors of an accessory for an electronic device, wherein the accessory includes first and second wireless charging coils, the one or more programs including instructions for:
 in a first mode, while the accessory is inductively coupled to the electronic device and the electronic device is not connected to a wired power source, transmitting wireless power signals to the electronic device using the first wireless charging coil; 
 in a second mode, while the accessory is inductively coupled to the electronic device and while the electronic device is connected to a wired power source, receiving wireless power signals from the electronic device using the first wireless charging coil; and 
 in a third mode, while the accessory is inductively coupled to both the electronic device and a power transmitting device, transmitting wireless power signals to the electronic device using the first wireless charging coil while receiving wireless power signals using the second wireless charging coil. 
 
     
     
       18. The non-transitory computer-readable storage medium of  claim 17 , wherein the one or more programs further include instructions for:
 in the first mode, placing the second wireless charging coil on standby; and 
 in the second mode, placing the second wireless charging coil on standby. 
 
     
     
       19. The non-transitory computer-readable storage medium of  claim 17 , wherein the first wireless charging coil is interposed between the second wireless charging coil and the electronic device when the accessory is inductively coupled to the electronic device and wherein the second wireless charging coil is interposed between the first wireless charging coil and the power transmitting device while the accessory is inductively coupled to both the electronic device and a power transmitting device. 
     
     
       20. A method of operating an accessory for an electronic device, wherein the accessory includes first and second wireless charging coils, the method comprising:
 in a first mode, while the accessory is inductively coupled to the electronic device and the electronic device is not connected to a wired power source, transmitting wireless power signals to the electronic device using the first wireless charging coil; 
 in a second mode, while the accessory is inductively coupled to the electronic device and while the electronic device is connected to a wired power source, receiving wireless power signals from the electronic device using the first wireless charging coil; and 
 in a third mode, while the accessory is inductively coupled to both the electronic device and a power transmitting device, transmitting wireless power signals to the electronic device using the first wireless charging coil while receiving wireless power signals using the second wireless charging coil. 
 
     
     
       21. The method of  claim 20 , further comprising:
 in the first mode, placing the second wireless charging coil on standby; and 
 in the second mode, placing the second wireless charging coil on standby.

Description:
This application claims the benefit of provisional patent application No. 63/047,797, filed Jul. 2, 2020, provisional patent application No. 63/047,779, filed Jul. 2, 2020, and provisional patent application No. 63/061,664, filed Aug. 5, 2020, which are hereby incorporated by reference herein in their entireties. 
     FIELD 
     This relates generally to power systems, and, more particularly, to wireless power systems for charging electronic devices. 
     BACKGROUND 
     In a wireless charging system, a wireless power transmitting device such as a charging mat wirelessly transmits power to a wireless power receiving device such as a portable electronic device. The wireless power receiving device has a coil and rectifier circuitry. The coil receives alternating-current wireless power signals from the wireless charging mat. The rectifier circuitry converts the received signals into direct-current power. 
     SUMMARY 
     A wireless power system may include one or more wireless power transmitting devices, one or more wireless power receiving devices, and one or more wireless power transmitting and receiving devices. The wireless power transmitting device may include a coil and wireless power transmitting circuitry coupled to the coil. The wireless power transmitting circuitry may be configured to transmit wireless power signals with the coil. The wireless power receiving device may include a coil that is configured to receive wireless power signals from the wireless power transmitting device and rectifier circuitry that is configured to convert the wireless power signals to direct current power. The wireless power transmitting and receiving device may include at least one coil and both wireless power transmitting circuitry and wireless power receiving circuitry. 
     An electronic device (that is capable of both transmitting and receiving wireless power) may be physically and inductively coupled to a removable case (that is also capable of both transmitting and receiving wireless power). The removable case may have first and second wireless charging coils with a battery interposed between the first and second wireless charging coils. The electronic device and removable case may optionally be placed on a power transmitting device. 
     The removable case may be operable in a number of different modes. When the electronic device is not tethered to mains power using a power cable, the removable case may transmit wireless power signals to the electronic device using the first wireless charging coil. When the electronic device is tethered to mains power using a power cable, the removable case may receive wireless power signals from the electronic device using the first wireless charging coil. When the removable case is inductively coupled to both the power transmitting device and the electronic device, the second wireless charging coil may receive wireless power signals from the power transmitting device and the first wireless charging coil may transmit wireless power signals to the electronic device. 
     The electronic device may be operable in a transmitting mode and a receiving mode. When the electronic device is not connected to a wired power source, the electronic device may operate in the receiving mode. When the electronic device is connected to a wired power source, the electronic device may operate in the transmitting mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless power system in accordance with an embodiment. 
         FIG. 2  is a circuit diagram of illustrative wireless power transmitting and receiving circuitry in accordance with an embodiment. 
         FIG. 3  is a top view of an illustrative removable accessory that may be included in a wireless power system in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative wireless power system including an untethered device inductively coupled to a removable accessory in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative wireless power system including an untethered device inductively coupled to a removable accessory that is inductively coupled to a power transmitting device in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative wireless power system including a tethered device inductively coupled to a removable accessory in accordance with an embodiment. 
         FIG. 7  is a state diagram of illustrative modes of operation for a removable accessory in a wireless power system in accordance with an embodiment. 
         FIG. 8  is a state diagram of illustrative modes of operation for an electronic device in a wireless power system in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system may include one or more electronic devices that transmit wireless power, one or more electronic devices that receive wireless power, and one or more electronic devices that both transmit and receive wireless power. The wireless power transmitting device may be a wireless charging mat or wireless charging puck, as examples. The wireless power receiving device may be a device such as a wrist watch, cellular telephone, tablet computer, laptop computer, or other electronic equipment, as examples. The wireless power transmitting and receiving device may be an electronic device case (e.g., a case for a cellular telephone) or other type of electronic device. The wireless power transmitting device may wirelessly transmit power to a wireless power receiving device. The wireless power receiving device uses power from the wireless power transmitting device for powering the device and for charging an internal battery. 
     Wireless power is transmitted from the wireless power transmitting device to the wireless power receiving device using one or more wireless power transmitting coils. The wireless power receiving device has one or more wireless power receiving coils coupled to rectifier circuitry that converts received wireless power signals into direct-current power. 
     In one illustrative configuration, an electronic device such as a cellular telephone may be configured to receive both wired and wireless power. The cellular telephone may include a coil that can either transmit or receive wireless power. The cellular telephone may also include a charging port that is configured to receive wired power from a charging cable that is connected to a wall outlet (e.g., mains power supply) through a power cable and a voltage converter such as an alternating current (AC) to Universal Serial Bus (USB) power adapter. The electronic device may be operable with a charging case that is also capable of both transmitting and receiving wireless power. In general, when the electronic device is inductively coupled to the charging case, the electronic device may receive wireless power from the charging case. When the electronic device receives wired power from the charging cable, the electronic device may transmit wireless power to the charging case. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , wireless power system  8  may include one or more wireless power transmitting devices such as wireless power transmitting device  12 , one or more wireless power receiving devices such as wireless power receiving device  24 , and one or more electronic devices capable of both transmitting and receiving wireless power (either simultaneously or at separate times) such as wireless power transmitting and receiving device  18 . It should be understood that one or more of each type of device may be present in the wireless power system at any given time, with devices being added and removed from the system in a fluid manner. Additionally, one or more devices may switch between tethered (where the device receives power from a wall outlet or other power source) and untethered (where the device battery is used to power the device) states. The function of power transmitting and receiving device  18  may change depending upon the arrangement of the system at a given time. A power transmitting and receiving device may only transmit power in some scenarios, may only receive power in some scenarios, and may both transmit and receive power in some scenarios. A power transmitting device  12  may transmit power directly to a power receiving device  24  in some scenarios. In other scenarios, power transmitting device  12  may transmit power to a power transmitting and receiving device  18 , which then transmits the power to power receiving device  24 . The functionality of each device and inductive coupling between each device within the system may be updated as devices are added to and removed from the system. 
     Wireless power transmitting device  12  includes control circuitry  16 . Wireless power receiving device  24  includes control circuitry  30 . Wireless power transmitting and receiving device  18  includes control circuitry  78 . Control circuitry in system  8  such as control circuitry  16 , control circuitry  30 , and control circuitry  78  is used in controlling the operation of system  8 . This control circuitry may include processing circuitry associated with microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. The processing circuitry implements desired control and communications features in devices  12 ,  18 , and  24 . For example, the processing circuitry may be used in selecting coils, determining power transmission levels, processing sensor data and other data to detect foreign objects and perform other tasks, processing user input, handling negotiations between devices  12 ,  18 , and  24 , sending and receiving in-band and out-of-band data, making measurements, and otherwise controlling the operation of system  8 . 
     Control circuitry in system  8  may be configured to perform operations in system  8  using hardware (e.g., dedicated hardware or circuitry), firmware and/or software. Software code for performing operations in system  8  is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media) in control circuitry  8 . 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, or the like. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  16 ,  30 , and/or  78 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, a central processing unit (CPU) or other processing circuitry. 
     Power transmitting device  12  may be a stand-alone power adapter (e.g., a wireless charging mat or charging puck that includes power adapter circuitry), may be a wireless charging mat or puck that is connected to a power adapter or other equipment by a cable, may be a portable device, may be equipment that has been incorporated into furniture, a vehicle, or other system, may be a removable battery case, or may be other wireless power transfer equipment. Illustrative configurations in which wireless power transmitting device  12  is a wireless charging mat or puck are sometimes described herein as an example. 
     Power receiving device  24  may be a portable electronic device such as a wrist watch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, or other electronic equipment. Power transmitting device  12  may be connected to a wall outlet (e.g., an alternating current power source), may have a battery  32  for supplying power, and/or may have another source of power. Power transmitting device  12  may have an alternating-current (AC) to direct-current (DC) power converter such as AC-DC power converter  14  for converting AC power from a wall outlet or other power source into DC power. DC power may be used to power control circuitry  16 . During operation, a controller in control circuitry  16  uses power transmitting circuitry  52  to transmit wireless power to power receiving circuitry  54  of device  24 . For simplicity, an example is described herein of power transmitting device  12  transmitting wireless power to power receiving device  24 . However, it should be understood that a power transmitting and receiving device  18  may substitute for one or both of the power transmitting device and the power receiving device during wireless power transfer operations. 
     Power transmitting circuitry  52  may have switching circuitry (e.g., inverter circuitry  61  formed from transistors) that is turned on and off based on control signals provided by control circuitry  16  to create AC current signals through one or more wireless power transmitting coils such as wireless power transmitting coil(s)  36 . These coil drive signals cause coil(s)  36  to transmit wireless power. Coils  36  may be arranged in a planar coil array or may be arranged to form a cluster of coils. In some arrangements, device  12  (e.g., a charging mat, puck, etc.) may have only a single coil. In other arrangements, a wireless charging device may have multiple coils (e.g., two or more coils, 5-10 coils, at least 10 coils. 10-30 coils, fewer than 35 coils, fewer than 25 coils, or other suitable number of coils). 
     As the AC currents pass through one or more coils  36 , alternating-current electromagnetic (e.g., magnetic) fields (wireless power signals  44 ) are produced that are received by one or more corresponding receiver coils such as coil(s)  48  in power receiving device  24 . In other words, one or more of coils  36  is inductively coupled to one or more of coils  48 . Device  24  may have a single coil  48 , at least two coils  48 , at least three coils  48 , at least four coils  48 , or other suitable number of coils  48 . When the alternating-current electromagnetic fields are received by coil(s)  48 , corresponding alternating-current currents are induced in coil(s)  48 . The AC signals that are used in transmitting wireless power may have any suitable frequency (e.g., 100-250 kHz, etc.). Rectifier circuitry such as rectifier circuitry  50 , which contains rectifying components such as synchronous rectification metal-oxide-semiconductor transistors arranged in a bridge network, converts received AC signals (received alternating-current signals associated with electromagnetic signals  44 ) from one or more coils  48  into DC voltage signals for powering device  24 . 
     The DC voltage produced by rectifier circuitry  50  (sometime referred to as rectifier output voltage Vrect) can be used in charging a battery such as battery  58  and can be used in powering other components in device  24 . For example, device  24  may include input-output devices  56 . Input-output devices  56  may include input devices for gathering user input and/or making environmental measurements and may include output devices for providing a user with output. As an example, input-output devices  56  may include a display (screen) for creating visual output, a speaker for presenting output as audio signals, light-emitting diode status indicator lights and other light-emitting components for emitting light that provides a user with status information and/or other information, haptic devices for generating vibrations and other haptic output, and/or other output devices. Input-output devices  56  may also include sensors for gathering input from a user and/or for making measurements of the surroundings of system  8 . Illustrative sensors that may be included in input-output devices  56  include three-dimensional sensors (e.g., three-dimensional image sensors such as structured light sensors that emit beams of light and that use two-dimensional digital image sensors to gather image data for three-dimensional images from light spots that are produced when a target is illuminated by the beams of light, binocular three-dimensional image sensors that gather three-dimensional images using two or more cameras in a binocular imaging arrangement, three-dimensional lidar (light detection and ranging) sensors, three-dimensional radio-frequency sensors, or other sensors that gather three-dimensional image data), cameras (e.g., infrared and/or visible cameras with respective infrared and/or visible digital image sensors and/or ultraviolet light cameras), gaze tracking sensors (e.g., a gaze tracking system based on an image sensor and, if desired, a light source that emits one or more beams of light that are tracked using the image sensor after reflecting from a user&#39;s eyes), touch sensors, buttons, capacitive proximity sensors, light-based (optical) proximity sensors such as infrared proximity sensors, other proximity sensors, force sensors, sensors such as contact sensors based on switches, gas sensors, pressure sensors, moisture sensors, magnetic sensors, audio sensors (microphones), ambient light sensors, optical sensors for making spectral measurements and other measurements on target objects (e.g., by emitting light and measuring reflected light), microphones for gathering voice commands and other audio input, distance sensors, motion, position, and/or orientation sensors that are configured to gather information on motion, position, and/or orientation (e.g., accelerometers, gyroscopes, compasses, and/or inertial measurement units that include all of these sensors or a subset of one or two of these sensors), sensors such as buttons that detect button press input, joysticks with sensors that detect joystick movement, keyboards, and/or other sensors. Device  12  may optionally have one or more input-output devices  70  (e.g., input devices and/or output devices of the type described in connection with input-output devices  56 ). Device  18  may optionally have one or more input-output devices  92  (e.g., input devices and/or output devices of the type described in connection with input-output devices  56 ). 
     Device  12 , device  18 , and/or device  24  may communicate wirelessly using in-band or out-of-band communications. Device  12  may, for example, have wireless transceiver circuitry  40  that wirelessly transmits out-of-band signals (e.g., to device  18  or device  24 ) using an antenna. Wireless transceiver circuitry  40  may be used to wirelessly receive out-of-band signals from device  18  or  24  using the antenna. Device  24  may have wireless transceiver circuitry  46  that transmits out-of-band signals. Receiver circuitry in wireless transceiver  46  may use an antenna to receive out-of-band signals. Device  18  may have wireless transceiver circuitry  80  that transmits out-of-band signals. Receiver circuitry in wireless transceiver  80  may use an antenna to receive out-of-band signals. Wireless transceiver circuitry  40 ,  46 , and  80  may also be used for in-band transmissions between devices  12 ,  24 , and  18  using coils  36 ,  48 , and  90 . 
     Frequency-shift keying (FSK) and/or amplitude-shift keying (ASK) may be used to convey in-band data between devices  12 ,  18 , and  24 . Power may be conveyed wirelessly during these FSK and ASK transmissions. 
     It is desirable for power transmitting device  12 , power transmitting and receiving device  18 , and power receiving device  24  to be able to communicate information such as received power, battery states of charge, and so forth, to control wireless power transfer. However, the above-described technology need not involve the transmission of personally identifiable information in order to function. Out of an abundance of caution, it is noted that to the extent that any implementation of this charging technology involves the use of personally identifiable information, implementers should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     Control circuitry  16  has external object measurement circuitry  41  that may be used to detect external objects on the charging surface of the housing of device  12  (e.g., on the top of a charging mat or, if desired, to detect objects adjacent to the coupling surface of a charging puck). The charging surface may be formed by a planer outer surface of the upper housing wall of device  12  or may have other shapes (e.g., concave or convex shapes, etc.). In arrangements in which device  12  forms a charging puck, the charging puck may have a surface shape that mates with the shape of device  24 . A puck or other device  12  may, if desired, have magnets that removably attach device  12  to device  24  (e.g., so that coil  48  aligns with coil  36  during wireless charging). 
     Circuitry  41  can detect foreign objects such as coils, paper clips, and other metallic objects and can detect the presence of wireless power receiving devices  24  (e.g., circuitry  41  can detect the presence of one or more coils  48  and/or magnetic core material associated with coils  48 ). During object detection and characterization operations, external object (foreign object) measurement circuitry  41  can be used to make measurements on coil(s)  36  such as Q-factor measurements, resonant frequency measurements, and/or inductance measurements that can indicate whether coil  48  is present and/or whether foreign objects such as coins or paperclips are present. Measurement circuitry can also be used to make sensor measurements using a capacitive sensor, can be used to make temperature measurements, and/or can otherwise be used in gathering information indicative of whether a foreign object or other external object (e.g., device  18  or  24 ) is present on device  12 . 
     In some configurations, the control circuitry of device  12  (e.g., circuitry  41  and/or other control circuitry  16 ) can implement a power counting foreign object detection scheme. With this approach, device  12  receives information from device  24  (e.g., via in-band communications) indicating the amount of power that device  24  is wirelessly receiving (e.g., 4.5 W). Device  12  knows how much power (e.g., 5.0 W) is being transmitted (e.g., because device  12  knows the magnitude of the signal being used to drive coil  36  from inverter  61 ). By comparing the transmitted power (e.g., 5.0 W) to the received power (e.g., 4.5 W), device  12  can determine whether wireless power is being dissipated due to eddy currents flowing in a foreign object. If the dissipated power (e.g., 0.5 W in this example) is more than a predetermined threshold amount or if the efficiency of the wireless power transfer process is lower than expected, device  12  can conclude that a foreign object is present. Power counting techniques such as these may be used in conjunction with capacitive sensing foreign object detection techniques and/or other external object measurement operations performed using circuitry  41 . 
     In some embodiments, measurement circuitry  41  of control circuitry  16  contains signal generator circuitry (e.g., oscillator circuitry for generating AC probe signals at one or more probe frequencies, a pulse generator that can create impulses so that impulse responses can be measured) and/or uses the transmission of wireless power signals from device  12  to energize the coils in system  8 . Circuitry  41  may also include circuits (e.g., analog-to-digital converter circuits, filters, analog combiners, digital processing circuitry, etc.) to measure the response of system  8 . 
     Power transmitting and receiving device  18  may be a wireless charging mat or puck that is connected to a power adapter (e.g., an AC to USB power adapter) or other equipment by a cable, may be equipment that has been incorporated into furniture, a vehicle, or other system, may be a removable battery case, may be a portable electronic device such as a wrist watch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, or other electronic equipment. Power transmitting and receiving device  18  is capable of both transmitting and receiving wireless power. Power transmitting and receiving device  18  therefore may include power transmitting components, similar to power transmitting device  12 . Power transmitting and receiving device  18  may also include power receiving components, similar to power receiving device  24 . 
     Power transmitting and receiving device  18  may have an alternating-current (AC) to direct-current (DC) power converter such as AC-DC power converter  96  for converting AC power from a wall outlet or other power source into DC power. DC power may be used to power control circuitry  78 . Control circuitry  78  includes wireless transceiver circuitry  80  for in-band communications (using coils  90 ) and out-of-band communications (using an antenna). Control circuitry  78  may also optionally include measurement circuitry  82  (e.g., measurement circuitry of the type described in connection with measurement circuitry  41 ). 
     Wireless power circuitry  84  in device  18  may include both an inverter  86  and a rectifier  88 . Inverter circuitry  86  (e.g., formed from transistors) may be turned on and off based on control signals provided by control circuitry  78  to create AC current signals through one or more coils such as coil(s)  90 . These coil drive signals cause coil(s)  90  to transmit wireless power. Coils  90  may be arranged in a planar coil array or may be arranged to form a cluster of coils. In some arrangements, device  18  may have only a single coil. In other arrangements, device  18  may have multiple coils (e.g., two or more coils, 5-10 coils, at least 10 coils, 10-30 coils, fewer than 35 coils, fewer than 25 coils, or other suitable number of coils). 
     As the AC currents pass through one or more coils  90 , alternating-current electromagnetic (e.g., magnetic) fields (wireless power signals  44 ) are produced that are received by one or more corresponding receiver coils such as coil(s)  48  in power receiving device  24 . In other words, one or more of coils  90  may be inductively coupled to one or more of coils  48 . 
     Power transmitting and receiving device  18  may also receive wireless power (e.g., from power transmitting device  12 ). Coil(s)  90  may receive alternating-current electromagnetic fields from transmitting coils  36 , resulting in corresponding alternating-current currents in coil(s)  90 . Rectifier circuitry such as rectifier circuitry  88 , which contains rectifying components such as synchronous rectification metal-oxide-semiconductor transistors arranged in a bridge network, converts received AC signals (received alternating-current signals associated with electromagnetic signals  44 ) from one or more coils  90  into DC voltage signals for powering device  18 . The DC voltage produced by rectifier circuitry  88  can be used in charging a battery such as battery  94  and can be used in powering other components in device  18 . 
     The depiction of alternating-electromagnetic fields between each type of device in  FIG. 1  is merely illustrative (to show the type of inductive coupling that is possible). In practice, alternating-electromagnetic fields will only be conveyed between select devices within the system. For example, transmitting device  12  may transmit power to device  24  and device  18  (while device  18  does not separately transmit power to device  18 ). In another example, transmitting device  12  transmits power to device  18 , which transmits power to  24  (without direct exchange of power from device  12  to device  24 ). 
     In some applications, power transmitting and receiving device  18  only transmits wireless power (e.g., using inverter  86  and coil(s)  90 ). In some applications, power transmitting and receiving device  18  only receives wireless power (e.g., using rectifier  88  and coil(s)  90 ). In some applications, power transmitting and receiving device simultaneously receives and transmits wireless power. When simultaneously receiving and transmitting wireless power, device  18  may optionally perform both the power transmitting and power receiving operations associated with inverter  86  and rectifier  88  (e.g., device  18  uses the rectifier to charge the battery and operate the device and independently uses the inverter to transmit a desired amount of power). Alternatively, device  18  may relay received wireless power signals without rectifying the power. Device  18  may include only one coil that is used for both wireless power transmission and wireless power reception. Alternatively, device  18  may have at least one dedicated wireless power transmitting coil and at least one dedicated wireless power receiving coil. Device  18  may have multiple coils that are all used for both wireless power transmission and wireless power reception. Different coils in device  18  may optionally be shorted together in different modes of operation. 
       FIG. 2  is a circuit diagram of illustrative wireless charging circuitry for system  8 . Wireless charging circuitry of a power transmitting device  12  and a power receiving device  24  is shown. However, it should be understood that device  18  may have the corresponding components for both power transmission and power reception and may be used in place of either device  12  and/or device  24  if desired. As shown in  FIG. 2 , circuitry  52  may include inverter circuitry such as one or more inverters  61  or other drive circuitry that produces wireless power signals that are transmitted through an output circuit that includes one or more coils  36  and capacitors such as capacitor  71 . In some embodiments, device  12  may include multiple individually controlled inverters  61 , each of which supplies drive signals to a respective coil  36 . In other embodiments, an inverter  61  is shared between multiple coils  36  using switching circuitry. 
     During operation, control signals for inverter(s)  61  are provided by control circuitry  16  at control input  74 . A single inverter  61  and single coil  36  is shown in the example of  FIG. 2 , but multiple inverters  61  and multiple coils  36  may be used, if desired. In a multiple coil configuration, switching circuitry (e.g., multiplexer circuitry) can be used to couple a single inverter  61  to multiple coils  36  and/or each coil  36  may be coupled to a respective inverter  61 . During wireless power transmission operations, transistors in one or more selected inverters  61  are driven by AC control signals from control circuitry  16 . The relative phase between the inverters can be adjusted dynamically. For example, a pair of inverters  61  may produce output signals in phase or out of phase (e.g., 180 degrees out of phase). 
     The application of drive signals using inverter(s)  61  (e.g., transistors or other switches in circuitry  52 ) causes the output circuits formed from selected coils  36  and capacitors  71  to produce alternating-current electromagnetic fields (signals  44 ) that are received by wireless power receiving circuitry  54  using a wireless power receiving circuit formed from one or more coils  48  and one or more capacitors  72  in device  24 . 
     If desired, the relative phase between driven coils  36  (e.g., the phase of one of coils  36  that is being driven relative to another adjacent one of coils  36  that is being driven) may be adjusted by control circuitry  16  to help enhance wireless power transfer between device  12  and device  24 . Rectifier circuitry  50  is coupled to one or more coils  48  (e.g., a pair of coils) and converts received power from AC to DC and supplies a corresponding direct current output voltage Vrect across rectifier output terminals  76  for powering load circuitry in device  24  (e.g., for charging battery  58 , for powering a display and/or other input-output devices  56 , and/or for powering other components). A single coil  48  or multiple coils  48  may be included in device  24 . 
     As previously mentioned, in-band transmissions using coils  36  and  48  may be used to convey (e.g., transmit and receive) information between devices  12  and  24 . With one illustrative configuration, frequency-shift keying (FSK) is used to transmit in-band data from device  12  to device  24  and amplitude-shift keying (ASK) is used to transmit in-band data from device  24  to device  12 . In other words, a device transmitting wireless power may use FSK to transmit in-band data to a device receiving wireless power (regardless of whether either device is a dedicated power transmitting/receiving device  12 / 24  or a power receiving and transmitting device  18 ). A device receiving wireless power may use ASK to transmit in-band data to a device transmitting wireless power (regardless of whether either device is a dedicated power transmitting/receiving device  12 / 24  or a power receiving and transmitting device  18 ). 
     Power may be conveyed wirelessly from device  12  to device  24  during these FSK and ASK transmissions. While power transmitting circuitry  52  is driving AC signals into one or more of coils  36  to produce signals  44  at the power transmission frequency, wireless transceiver circuitry  40  may use FSK modulation to modulate the power transmission frequency of the driving AC signals and thereby modulate the frequency of signals  44 . In device  24 , coil  48  is used to receive signals  44 . Power receiving circuitry  54  uses the received signals on coil  48  and rectifier  50  to produce DC power. At the same time, wireless transceiver circuitry  46  monitors the frequency of the AC signal passing through coil(s)  48  and uses FSK demodulation to extract the transmitted in-band data from signals  44 . This approach allows FSK data (e.g., FSK data packets) to be transmitted in-band from device  12  to device  24  with coils  36  and  48  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  36  and  48 . 
     In-band communications between device  24  and device  12  may use ASK modulation and demodulation techniques. Wireless transceiver circuitry  46  transmits in-band data to device  12  by using a switch (e.g., one or more transistors in transceiver  46  that are coupled coil  48 ) to modulate the impedance of power receiving circuitry  54  (e.g., coil  48 ). This, in turn, modulates the amplitude of signal  44  and the amplitude of the AC signal passing through coil(s)  36 . Wireless transceiver circuitry  40  monitors the amplitude of the AC signal passing through coil(s)  36  and, using ASK demodulation, extracts the transmitted in-band data from these signals that was transmitted by wireless transceiver circuitry  46 . The use of ASK communications allows ASK data bits (e.g., ASK data packets) to be transmitted in-band from device  24  to device  12  with coils  48  and  36  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  36  and  48 . 
     The example of FSK modulation being used to convey in-band data from power transmitting device  12  to power receiving device  24  and ASK modulation being used to convey in-band data from power receiving device  24  to power transmitting device  12  is merely illustrative. In general, any desired communication techniques may be used to convey information from power transmitting device  12  to power receiving device  24  and from power receiving device  24  to power transmitting device  12 . In general, wireless power may simultaneously be conveyed between devices during in-band communications (using ASK or FSK). 
     The power transmission frequency used for transmission of wireless power may be, for example, a predetermined frequency of about 125 kHz, at least 80 kHz, at least 100 kHz, between 100 kHz and 205 kHz, less than 500 kHz, less than 300 kHz. or other suitable wireless power frequency. In some configurations, the power transmission frequency may be negotiated in communications between devices  12  and  24 . In other configurations, the power transmission frequency may be fixed. 
     It has been described that power may be simultaneously conveyed between devices while using in-band communication for data transmission between the devices. In other words, in some examples in-band communications may rely on modulation of the power transmission signal (e.g., modulating the power transmission frequency or modulating amplitude of a signal at the power transmission frequency). However, other communication techniques may be used that do not rely on modulation of the power transmission signals. For example, signals (sometimes referred to as in-band signals) may be conveyed between coils in the system at a frequency that is different than the power transmission frequency. Signals (at the same frequency or a different frequency than the power transmission frequency) that are conveyed using the coils (e.g., coils  36 ,  48 , and  90 ) may be considered in-band signals. 
     Moreover, it should be noted that in-band communication may occur between devices before the devices agree upon a power transfer rate, power transmission frequency, etc. After initial detection and inductive coupling, devices may go through a handshake process to determine compatibility, negotiate power transfer frequency, negotiate power transfer rate, etc. During this process, in-band communication may involve FSK and/or ASK modulation of signals at the power transmission frequency. Therefore, wireless power is transmitted during this process. This is advantageous as it allows the devices to complete the handshake process even if the power receiving device has little or no remaining battery power. This transmission of wireless power during in-band communications may occur during the handshake process even if, ultimately, the negotiations between the devices result in no sustained transmission of wireless power (e.g., even if the devices do not enter a dedicated power transfer phase). 
     The aforementioned FSK and ASK modulation and demodulation techniques may be used to transmit data packets between any two devices within system  8 . Each data packet may include numerous data bits (sometimes referred to as bits). The data bits may be grouped into bytes, with each byte including any desired number of bits (e.g., 8 bits). 
     At least one coil in power transmitting and receiving device  18  may be used for transmitting or receiving wireless power (depending on the conditions within the wireless charging system). However, the coil does not transmit and receive wireless power at the same time. Therefore, control circuitry within the device may be used to control whether the coil is used for transmitting or receiving wireless power at any given time. 
     A device in wireless charging system  8  may optionally be coupled (e.g., physically coupled) to a removable accessory such as a case. The case may optionally have wireless charging functionality (e.g., the case may be capable of receiving and/or transmitting wireless power). When the device is physically coupled to the removable accessory and the removable accessory has wireless charging functionality, the device and the removable accessory may also be inductively coupled.  FIG. 3  is a top view of an accessory such as a removable case. 
     Removable accessory  102  (sometimes referred to as a removable case or removable cover) may have any suitable shape that allows case  102  to mate with another device. Accessory  102  and the device to which it is coupled may each serve as a power transmitting device, a power receiving device, or a power transmitting and receiving device. The device held by accessory  102  may be a portable electronic device such as a wrist watch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, or other electronic equipment. 
     In the example of  FIG. 3 , case  102  includes a rectangular recess with a wall  102 R surrounded by peripheral sidewalls  102 W and/or other suitable coupling structures (straps, clips, a sleeve, corner pockets, etc.) that allow cover  102  to receive and couple to the additional device. Wall  102 R may be positioned adjacent a rear face of the device when coupled to the device and therefore may sometimes be referred to as rear wall  102 R. When it is desired to protect the additional device in case  102 , the device (e.g., a housing of the device) may be press fit into a recess formed by the sidewalls  102 W and/or rear wall  102 R of cover  102 , coupled to cover  102  using magnets, clips, or straps, or otherwise coupled to cover  102 . Cover  102  may be formed from fabric, leather, polymer, other materials, and/or combinations of these materials. As previously mentioned, cover  102  may in some embodiments include one or more coils that each transmit and/or receives wireless power. 
       FIG. 4  is a cross-sectional side view showing device  100  inductively coupled to removable case  102 . Device  100  and removable case  102  in  FIG. 4  are also physically coupled (e.g., the removable case receives device  100 ). Device  100  may have a housing  164 . Housing  164  may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Case  102  may have a recess that conforms to the shape of housing  164 . In one illustrative example, device  100  is a power transmitting and receiving device (e.g., device  18  in  FIG. 1 ). In general, device  100  may be a removable battery case, a portable electronic device such as a wrist watch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, or other electronic equipment. Herein, an example will be described where device  100  is a portable electronic device such as a cellular telephone that is capable of both transmitting and receiving wireless power. 
     Removable case  102  may include one or more dielectric layers  142  (e.g., a bulk dielectric material) such as one or more layers of fabric, leather, polymer (e.g., polyurethane), other materials, and/or combinations of these materials. One or more coils may be embedded in the one or more layers of dielectric material. 
     As shown in  FIG. 4 , removable case  102  may include a first coil  112  and a second coil  114 . As shown, coil  114  may be adjacent to a first surface  106  of removable case  102  whereas coil  112  may be adjacent to a second surface  108  of removable case  102 . The removable case may be configured such that surface  106  is positioned adjacent to device  100  when removable case  102  is physically coupled to device  100 . Consequently, coil  114  may be positioned adjacent to device  100  when removable case  102  is physically (and inductively) coupled to device  100 . Coil  114  is interposed between device  100  and coil  112  when removable case  102  is physically (and inductively) coupled to device  100 . Battery  94  may be interposed between coils  112  and  114 , as shown in  FIG. 4 . 
     Accordingly, coil  114  may be used to transmit wireless power to device  100 . Device  100  may include a coil  122  that is configured to receive wireless power signals from coil  114 . 
     Coils  112 ,  114 , and  122  may be capable of transmitting or receiving wireless power signals. When coil  114  is used to transmit wireless power to coil  122 , inverter circuitry (e.g., inverter  86  in  FIG. 1 ) can drive the coil  114  to generate magnetic flux. Coil  122  in device  100  may be coupled to rectifier circuitry (e.g., rectifier  88  in  FIG. 1 ). The rectifier circuitry converts received AC signals from coil  122  into DC voltage signals for powering device  100  and/or charging a battery in device  100 . 
     When devices  100  and  102  are inductively coupled in the absence of an additional device, coil  112  in removable case  102  may be on standby. When coil  112  is on standby (e.g., in a standby mode or standby state), the coil does not continuously transmit or receive wireless power signals. In other words, the standby mode occurs when the coil has not entered a dedicated power transfer phase. While coil  112  is in the standby mode, device  102  may intermittently check for the presence of another device (e.g., using coil  112  or another sensor in the device) adjacent to surface  108 . For example, coil  112  may intermittently transmit low power pings while on standby in order to monitor for another device being added to the system. Alternatively or in addition, a magnetic sensor (e.g., a Hall effect sensor), another type of sensor, a near-field communication (NFC) antenna, or another desired component may be used to detect another device adjacent to surface  108  of device  102 . The coil  112  may additionally be prepared to send a transmission (e.g., an ASK transmission) while on standby. If coil  112  receives a digital ping from another device in the system, the coil may immediately respond with the transmission. 
     In some situations device  100  and accessory  102  may be physically coupled together and may be placed on a power transmitting device. A situation of this type is shown in  FIG. 5 . In this scenario, power transmitting device  104  may transmit wireless power to device  102 . At the same time, device  102  may transmit wireless power to device  100 . 
     Similar to as discussed in connection with  FIG. 1 , the power transmitting device  104  in  FIG. 5  may be a wireless charging mat, wireless charging puck, a battery case (e.g., a dedicated wireless power transmitting device), or another electronic device (e.g., a wireless power transmitting and receiving device). An example is described herein where the power transmitting device  104  is a wireless charging mat. The wireless charging mat  104  may be connected to a wall outlet (e.g., an alternating current power source). Using power from this power source, the wireless charging mat  104  may transmit wireless power to one or more devices. 
     In  FIG. 5 , coil  126  in power transmitting device  104  may transmit wireless power signals to coil  112  in accessory  102 . Inverter circuitry may drive the coil  126  to generate magnetic flux. Coil  112  in device  102  may be coupled to rectifier circuitry (e.g., rectifier  88  in  FIG. 1 ). The rectifier circuitry converts received AC signals from coil  112  into DC voltage signals for powering device  102  and/or charging a battery in device  102 . Using power from the battery or directly from the rectifier, inverter circuitry (e.g., inverter  86  in  FIG. 1 ) may drive the coil  114  to generate magnetic flux that is transferred to coil  122  in device  100 . In another possible arrangement. AC power from the rectifier circuitry may be directly relayed to the inverter circuitry that drives  114  (instead of rectifying to DC then inverting back to AC). Coil  122  in device  100  may be coupled to rectifier circuitry (e.g., rectifier  88  in  FIG. 1 ). The rectifier circuitry converts received AC signals from coil  122  into DC voltage signals for powering device  100  and/or charging a battery in device  100 . 
     Coils  112 ,  114 ,  122 , and  126  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. 
     Devices  100 ,  102 , and  104  may also optionally include magnetic alignment structures. As shown in  FIGS. 4 and 5 , device  100  includes a magnetic alignment structure  124 . Device  102  includes a first magnetic alignment structure  118  and a second magnetic alignment structure  116 . Device  104  includes a magnetic alignment structure  128 . Each magnetic alignment structure in the system may magnetically couple with a corresponding magnetic alignment structure in the system. For example, alignment structure  128  in transmitting device  104  may magnetically couple with alignment structure  116  in removable accessory  102 . When the alignment structure  128  in device  104  is coupled to the alignment structure  116  in device  102 , the coil  126  may be aligned with the coil  112 . Therefore, the magnetic alignment structures ensure proper alignment of the receiving coil ( 112 ) relative to the transmitting coil ( 126 ). 
     Alignment structure  118  in removable accessory  102  may magnetically couple with alignment structure  124  in device  100 . When the alignment structure  118  in device  102  is coupled to the alignment structure  124  in device  100 , the coil  114  may be aligned with the coil  122 . Therefore, the magnetic alignment structures ensure proper alignment of the receiving coil ( 122 ) relative to the transmitting coil ( 114 ). 
     Magnetic alignment structures  128 ,  116 ,  118 , and  124  may be permanent magnets (e.g., formed from hard magnetic materials that retain their magnetism over time). The magnetic alignment structures may laterally surround a respective coil. The alignment structures may sometimes be described as annular or circular. Magnetic alignment structure  128  may have a central opening with coil  126  formed in the central opening. Alignment structure  128  and coil  126  may be concentric. This example is merely illustrative. Other arrangements may be used if desired. For example, alignment structure  128  may be formed as two discrete permanent magnets on opposing sides of coil  126 . In another example, a plurality of discrete permanent magnets may be arranged in a circular (annular) pattern (e.g., dotted lines forming a circle) around coil  126 . The discrete permanent magnets may have an arcuate arrangement. The aforementioned magnetic alignment structure and coil arrangements described relative to alignment structure  128  and coil  126  may apply to any of the sets of alignment structures and coils (e.g., alignment structure  116  and coil  112 , alignment structure  118  and coil  114 , and alignment structure  124  and coil  122 ). 
     Each coil (e.g., coils  112 ,  114 ,  122 , and  126 ) may optionally have a corresponding magnetic core of any desired design. In one possible arrangement, a magnetic core may be included with a pot-core design (e.g., an enclosure with a ring-shaped hollow portion that receives the coil). In yet another possible arrangement, a winding on a bar-shaped ferrite may be used. Any desired magnetic core and coil design may be used (e.g., a U-shaped core, a C-shaped core, an E-shaped core, a toroidal core, etc.). Each coil may have any desired number of windings. The precise geometry of the coils and magnetic cores in devices  100 ,  102 , and  104  may be tailored to the specific design. Device  100  may be designed to cooperate specifically with wireless power transmitting device  104 . This is, however, merely illustrative. Device  100  may, in comes cases, not be specifically designed to cooperate with power transmitting device  104 . In general, each device may have different coil arrangements, different (or no) magnetic elements (e.g., magnetic cores), different coil and magnetic element sizes, different coil and magnetic element shapes, and other different characteristics. 
     In both  FIGS. 4 and 5 , coil  114  in device  102  transmits wireless power to coil  122  in device  100 . This is the case regardless of whether accessory  102  and device  100  are in the presence of charging mat  104  (as in  FIG. 5 ) or not (as in  FIG. 4 ). Removable accessory  102  transmitting wireless power to device  100  may be the default configuration for removable accessory  102  and device  100  in the absence of a wired power source connected to device  100 . In  FIGS. 4 and 5 , device  100  is not connected to a wired power source (e.g., device  100  is untethered). Therefore, device  100  receives power from removable accessory  102 . However, if device  100  is connected to a wired power source (e.g., device  100  is tethered), device  100  may instead transmit power to removable accessory  102 . An arrangement of this type is shown in  FIG. 6 . 
     As shown in  FIG. 6 , device  100  may include a charging port  132 . The charging port may be an opening in the device housing that is configured to connect to a wired power source such as cable  134 . Cable  134  may have a connector that is inserted into the charging port  132  to connect device  100  to wired power. The cable  134  may be connected to a wall outlet (e.g., mains power supply) through a voltage converter such as an AC to USB power adapter. 
     When device  100  is connected to a wired power source as in  FIG. 6  (e.g., when device  100  is tethered to a USB or Lightning power source), the device may switch from a receiving mode in which coil  122  receives wireless power to a transmitting mode in which coil  122  transmit wireless power. In the transmitting mode, inverter circuitry may drive the coil  122  to generate magnetic flux. Coil  114  in device  102  may be coupled to rectifier circuitry (e.g., rectifier  88  in  FIG. 1 ). The rectifier circuitry converts received AC signals from coil  114  into DC voltage signals for powering device  102  and/or charging a battery in device  102 . When devices  100  and  102  are inductively coupled while device  100  is connected to wired power, coil  114  in removable case  102  may receive wireless power and coil  112  in removable case  102  may be on standby. 
       FIG. 7  is a state diagram showing illustrative modes of operation for the removable accessory  102  in system  8 . Removable accessory  102  may be operable in a transmitting mode  202  in which coil  114  transmits wireless power to device  100 . In the transmitting mode, the second coil ( 112 ) may be on standby. In the transmitting mode, inverter circuitry  86  (e.g., formed from transistors) coupled to coil  114  may be turned on and off based on control signals provided by control circuitry  78  to create AC current signals through coil  114 . These coil drive signals cause coil  114  to transmit wireless power to coil  122  in device  100 . 
     Removable accessory  102  may operate in the transmitting mode while the removable accessory is inductively coupled to device  100 , device  100  is not connected to a wired power source (e.g., while device  100  is untethered), and the removable accessory is not placed on an additional power transmitting device (e.g., not inductively coupled to an additional power transmitting device). 
     Removable accessory  102  may be operable in a relay mode  204  in which coil  112  receives wireless power from power transmitting device  104  and coil  114  transmits wireless power to device  100 . In the relay mode, rectifier circuitry converts received AC signals from coil  112  into DC voltage signals for powering device  102  and/or charging a battery in device  102 . Using power from the battery or directly from the rectifier circuitry, inverter circuitry  86  (e.g., formed from transistors) coupled to coil  114  may be turned on and off based on control signals provided by control circuitry  78  to create AC current signals through coil  114 . These coil drive signals cause coil  114  to transmit wireless power to coil  122  in device  100 . 
     Removable accessory  102  may operate in the relay mode while inductively coupled to device  100  and transmitting device  104 . 
     Removable accessory  102  may also be operable in a first coil receiving mode  206  in which coil  114  receives wireless power from coil  122  in device  100 . In the first coil receiving mode, the second coil ( 112 ) may be on standby. In the first coil receiving mode, rectifier circuitry converts received AC signals from coil  114  into DC voltage signals for powering device  102  and/or charging a battery in device  102 . In the first coil receiving mode (while the second coil  112  is on standby), device  102  may intermittently use coil  112  or another component such as a magnetic sensor or NFC antenna to check for the presence of an additional device (such as device  104  in  FIG. 5 ) adjacent to surface  108  and coil  112 . 
     Removable accessory  102  may operate in the first coil receiving mode while the removable accessory is inductively coupled to device  100 , device  100  is connected to a wired power source (e.g., while device  100  is tethered), and the removable accessory is not placed on an additional power transmitting device. 
     It should be noted that there are some additional circumstances in which removable accessory  102  may operate in the first coil receiving mode. In general, if the removable accessory is inductively coupled to device  100  while device  100  is untethered, removable accessory may default to the transmitting mode (or relay mode if the transmitter  104  is present). However, if the state of charge of the removable accessory is very low and the state of charge of device  100  is very high, removable accessory  102  may operate in the first coil receiving mode. Devices  100  and  102  may exchange state of charge information and switch removable accessory  102  into the first coil receiving mode if appropriate. As another example, a user may manually switch removable accessory  102  into the first coil receiving mode while removable accessory  102  is inductively coupled to device  100 . 
     Removable accessory  102  may also be operable in a second coil receiving mode  207  in which coil  112  receives wireless power (e.g., from coil  126  in device  104  or other power transmitting coil). In the second coil receiving mode, the first coil ( 114 ) may be on standby. In the second coil receiving mode, rectifier circuitry converts received AC signals from coil  112  into DC voltage signals for powering device  102  and/or charging a battery in device  102 . 
     While coil  114  is in the standby mode, device  102  may intermittently check for the presence of another device (e.g., using coil  114  or another sensor in the device) adjacent to surface  106 . For example, coil  114  may intermittently transmit low power pings while on standby in order to monitor for another device being added to the system. Alternatively or in addition, a magnetic sensor (e.g., a Hall effect sensor), another type of sensor, a near-field communication (NFC) antenna, or another desired component may be used to detect another device adjacent to surface  106  of device  102 . The coil  114  may additionally be prepared to send a transmission (e.g., an ASK transmission) while on standby. If coil  114  receives a digital ping from another device in the system, the coil may immediately respond with the transmission. 
     Removable accessory  102  may operate in the second coil receiving mode while the removable accessory is inductively coupled to device  104  and the removable accessory is not inductively coupled to another device ( 100 ). 
     It should be noted that the example of removable accessory  102  including first and second coils is merely illustrative. In some cases, removable accessory  102  may only include one coil. For example, coil  112  may be omitted and coil  114  (capable of transmitting or receiving wireless power) may still be included. 
       FIG. 8  is a state diagram showing illustrative modes of operation for device  100  in system  8 . Device  100  may be operable in a receiving mode  208  in which coil  122  receives wireless power (e.g., from coil  114  in removable accessory  102 ). The rectifier circuitry converts received AC signals from coil  122  into DC voltage signals for powering device  100  and/or charging a battery in device  100 . 
     Device  100  may operate in the receiving mode while device  100  is inductively coupled to device  102  and device  100  is not connected to a wired power source (e.g., device  100  is untethered). Device  100  may also operate in the receiving mode while device  100  is inductively coupled to device  104  without an intervening device ( 102 ). 
     Device  100  may also be operable in a transmitting mode  210  in which coil  122  transmits wireless power to device  102 . In the transmitting mode, inverter circuitry  86  (e.g., formed from transistors) coupled to coil  122  may be turned on and off based on control signals provided by control circuitry  78  to create AC current signals through coil  122 . These coil drive signals cause coil  122  to transmit wireless power to coil  114  in device  102 . 
     Device  100  may operate in the transmitting mode while device  100  is inductively coupled to removable accessory  102  and while device  100  is tethered to mains power through a power cable and a voltage converter such as an AC to USB adapter. 
     Similar to as previously mentioned, there are some additional circumstances in which device  100  may operate in the transmitting mode. In general, if the removable accessory  102  is inductively coupled to device  100  while device  100  is untethered, device  100  may default to the receiving mode  208 . However, if the state of charge of the removable accessory  102  is very low and the state of charge of device  100  is very high, device  100  may operate in the transmitting mode  210 . Devices  100  and  102  may exchange state of charge information and switch device  100  into the transmitting mode (and device  102  into its receiving mode) if appropriate. As another example, a user may manually switch device  100  into the transmitting mode while device is inductively coupled to removable accessory  102 . 
     Device  100  may therefore default to the receiving mode when coupled with removable accessory  102 . However, in response to being connected to wired power (e.g., at charging port  132 ), device  100  may switch to a transmitting mode and transmit wireless power to the removable accessory. In other words, being connected to wired power causes device  100  to switch from the receiving mode  208  to the transmitting mode  210  (and causes a corresponding mode switch in accessory  102 ). If the device  100  is then subsequently disconnected from the wired power source (e.g., untethered), device  100  may switch back to the receiving mode. In other words, being disconnected from wired power causes device  100  to switch from the transmitting mode  210  to the receiving mode  208  (and causes a corresponding mode switch in accessory  102 ). 
     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.

Metadata:
Filing Date: 20200909
Publication Date: 20210302
Grant Date: 20210302
Priority Date: 20200702
Inventors: MEHRABI, Arash
LISI, GIANPAOLO
MOUSSAOUI, ZAKI
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J7/0048", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J2207/20", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J7/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J2207/20", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 74683202