PATENT DOCUMENT

Publication Number: US-12100968-B2
Application Number: US-202117513581-A
Country: US
Kind Code: B2

Title: Wireless power mode switching

Abstract:
An electronic device (that is capable of both transmitting and receiving wireless power) may be physically and inductively coupled to a removable accessory (that only receives wireless power). The electronic device and removable accessory may optionally be placed on a power transmitting device. In response to the electronic device and removable accessory being placed on a wireless power transmitting device, the electronic device may switch from a power transmitting mode (in which the electronic device transmits wireless power to the removable accessory) to a power receiving mode (in which the electronic device receives wireless power from the wireless power transmitting device). To ensure the electronic device detects the wireless power transmitting device and switches to the power receiving mode in this scenario, the electronic device may transmit wireless power in bursts separated by sleep periods while in the power transmitting mode.

Claims:
What is claimed is: 
     
       1. An electronic device operable in a wireless charging system with an additional electronic device and a power transmitting device, the electronic device comprising:
 wireless power circuitry including a coil; and 
 control circuitry configured to:
 detect a first attachment to the additional electronic device; 
 in accordance with detecting the first attachment, enter a power transmitting mode that includes alternating first periods and second periods, wherein the coil transmits alternating-current wireless power signals to the additional electronic device in the first periods, and wherein the coil does not transmit alternating-current wireless power signals to the additional electronic device in the second periods; 
 during one of the second periods, detect a second attachment to the power transmitting device; and 
 in accordance with detecting the second attachment, switch from the power transmitting mode to a power receiving mode in which the coil receives wireless power signals from the power transmitting device. 
 
 
     
     
       2. The electronic device of  claim 1 , wherein detecting the second attachment comprises receiving a digital ping from the power transmitting device. 
     
     
       3. The electronic device of  claim 1 , wherein each one of the first periods has a first duration and wherein each one of the second periods has a second duration that is greater than the first duration. 
     
     
       4. The electronic device of  claim 1 , wherein the control circuitry is further configured to:
 switch from the power receiving mode to the power transmitting mode in response to being removed from a charging surface of the power transmitting device. 
 
     
     
       5. The electronic device of  claim 1 , wherein the additional electronic device has an additional coil that is interposed between the power transmitting device and the coil when the electronic device has the first and second attachments. 
     
     
       6. The electronic device of  claim 5 , wherein the additional coil is configured to siphon some of the wireless power signals from the power transmitting device when the electronic device has the first and second attachments. 
     
     
       7. The electronic device of  claim 1 , further comprising:
 a sensor that is sensitive to electromagnetism, wherein detecting the first attachment comprises detecting the presence of the additional electronic device using the sensor. 
 
     
     
       8. The electronic device of  claim 1 , further comprising:
 a first magnetic alignment structure that is configured to magnetically couple to a second magnetic alignment structure in the additional electronic device when the electronic device has the first attachment. 
 
     
     
       9. The electronic device of  claim 8 , wherein the first magnetic alignment structure and the coil are concentric. 
     
     
       10. The electronic device of  claim 8 , wherein the first magnetic alignment structure is configured to magnetically couple to a third magnetic alignment structure in the power transmitting device when the electronic device has the second attachment. 
     
     
       11. The electronic device of  claim 1 , wherein the additional electronic device has at least one dielectric layer that forms a planar surface and wherein the planar surface is configured to abut a rear face of the electronic device while the additional electronic device is attached to the electronic device. 
     
     
       12. The electronic device of  claim 1 , wherein the additional electronic device is a case having a rear wall and peripheral sidewalls that define a recess configured to receive the electronic device. 
     
     
       13. The electronic device of  claim 1 , wherein each one of the second periods has a duration that is greater than 50 milliseconds. 
     
     
       14. The electronic device of  claim 13 , wherein the alternating-current wireless power signals transmitted by the coil have a frequency between 100 kHz and 400 kHz. 
     
     
       15. A non-transitory computer-readable storage medium storing one or more programs configured to be executed by one or more processors of an electronic device operable in a wireless charging system with an additional electronic device and a power transmitting device, wherein the electronic device comprises wireless power circuitry including a coil, the one or more programs including instructions for:
 detecting a first attachment to the additional electronic device; 
 in accordance with detecting the first attachment, entering a power transmitting mode that includes alternating first periods and second periods, wherein the coil transmits alternating-current wireless power signals to the additional electronic device in the first periods, and wherein the coil does not transmit alternating-current wireless power signals to the additional electronic device in the second periods; 
 during one of the second periods, detecting a second attachment to the power transmitting device; and 
 in accordance with detecting the second attachment, switching from the power transmitting mode to a power receiving mode in which the coil receives wireless power signals from the power transmitting device. 
 
     
     
       16. The non-transitory computer-readable storage medium of  claim 15 , wherein detecting the second attachment comprises receiving a digital ping from the power transmitting device. 
     
     
       17. The non-transitory computer-readable storage medium of  claim 15 , wherein the one or more programs further include instructions for:
 switching from the power receiving mode to the power transmitting mode in response to being removed from a charging surface of the power transmitting device. 
 
     
     
       18. A method of operating an electronic device in a wireless charging system with an additional electronic device and a power transmitting device, wherein the electronic device comprises wireless power circuitry including a coil, the method comprising:
 detecting a first attachment to the additional electronic device; 
 in accordance with detecting the first attachment, entering a power transmitting mode that includes alternating first periods and second periods, wherein the coil transmits alternating-current wireless power signals to the additional electronic device in the first periods, and wherein the coil does not transmit alternating-current wireless power signals to the additional electronic device in the second periods; 
 during one of the second periods, detecting a second attachment to the power transmitting device; and 
 in accordance with detecting the second attachment, switching from the power transmitting mode to a power receiving mode in which the coil receives wireless power signals from the power transmitting device. 
 
     
     
       19. The method of  claim 18 , wherein detecting the second attachment comprises receiving a digital ping from the power transmitting device. 
     
     
       20. The method of  claim 18 , further comprising:
 switching from the power receiving mode to the power transmitting mode in response to being removed from a charging surface of the power transmitting device.

Description:
This application claims the benefit of provisional patent application No. 63/236,084, filed Aug. 23, 2021, which is hereby incorporated by reference herein in its entirety. 
    
    
     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 transmits wireless 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 accessory (that only receives wireless power). The removable accessory may have a wireless charging coil that is configured to receive wireless power from the electronic device when the removable accessory is coupled to the electronic device. The electronic device and removable accessory may optionally be placed on a power transmitting device. 
     In response to the electronic device and (attached) removable accessory being placed on a wireless power transmitting device, the electronic device may switch from a power transmitting mode (in which the electronic device transmits wireless power to the removable accessory) to a power receiving mode (in which the electronic device receives wireless power from the wireless power transmitting device). To ensure the electronic device detects the wireless power transmitting device and switches to the power receiving mode in this scenario, the electronic device may transmit wireless power in bursts separated by sleep periods while in the power transmitting mode. While the electronic device and (attached) removable accessory are on the wireless power transmitting device, the removable accessory may siphon some of the wireless power transmitted by the wireless power transmitting device to the electronic device. 
    
    
     
       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 electronic device attached 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 electronic device that is attached to a removable accessory and 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 an electronic device that is inductively coupled to a wireless power transmitting device without an intervening removable accessory in accordance with an embodiment. 
         FIG.  7    is a timing diagram showing illustrative operations of a charging puck and a cellular telephone 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. 
         FIG.  9    is a flowchart of illustrative operations performed by an electronic device in response to being attached to a removable accessory in accordance with an embodiment. 
         FIG.  10    is a flowchart of illustrative operations performed by an electronic device in response to being placed on a power transmitting mat while attached to a removable accessory 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 wristwatch, cellular telephone, tablet computer, laptop computer, an accessory such as a case, 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), cellular telephone, tablet computer, laptop computer, or other electronic equipment. 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. 
     In one illustrative configuration, an electronic device such as a cellular telephone may be configured to both receive and transmit wireless power. The cellular telephone may be operable with an accessory device that is configured to receive wireless power. The cellular telephone may optionally mate with the accessory device. When the cellular telephone is mated with the accessory device, the cellular telephone may transfer wireless power to the accessory device. When the cellular telephone and the mated accessory device are placed on a power transmitting device such as a charging puck, the cellular telephone may switch from a power transmitting mode to a power receiving mode and receive wireless power from the charging puck. The accessory device may siphon some of the power transmitted by the charging puck in this configuration. 
     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 wristwatch, 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., 100-400 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  (such as control circuitry  30 , input-output devices  56 , etc.). 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 . 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 ). 
     The example in  FIG.  1    of power receiving device  24  and power transmitting and receiving device  18  including batteries  58  and  94  respectively is merely illustrative. If desired, an electronic device may include a supercapacitor to store charge instead of a battery. For example, power receiving device  24  may include a supercapacitor in place of battery  58 . Battery  58  may therefore sometimes be referred to as power storage device  58  or supercapacitor  58 . Similarly, power transmitting and receiving device  18  may include a supercapacitor in place of battery  94 . Battery  94  may therefore sometimes be referred to as power storage device  94  or supercapacitor  94 . 
     Device  12 , device  18 , and/or device  24  may communicate wirelessly using in-band or out-of-band communications. In some examples, 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. In some examples, device  12  has 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 . 
     It is desirable for power transmitting device  12 , power transmitting and receiving device  18 , and power receiving device  24  to be able to communicate certain information such as received power 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. 
     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 ). Measurement circuitry  41  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 . 
     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 wristwatch, 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  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 power storage device  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 at least 80 kHz, at least 100 kHz, between 100 kHz and 205 kHz, less than 500 kHz, less than 300 kHz, between 100 kHz and 400 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). 
     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 wristwatch, 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   , accessory  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 accessory  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 accessory  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 accessory  102 , coupled to accessory  102  using magnets, clips, or straps, or otherwise coupled to accessory  102 . Accessory  102  may be formed from fabric, leather, polymer, other materials, and/or combinations of these materials. As previously mentioned, accessory  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 attached (e.g., the removable case  102  receives device  100 ). Device  100  may have a housing  164  and a wireless power coil  122  in the housing. 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 wristwatch, 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. Coil  122  in device  100  may either transmit wireless power or receive wireless power at a given time. 
     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. In general, device  102  may be a removable battery case, a portable electronic device such as a wristwatch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, another accessory device (e.g., a case), or other electronic equipment. Herein, an example will be described where device  102  is an accessory device such as a case that is configured to receive wireless power (but does not transmit wireless power). 
     As shown in  FIG.  4   , removable case  102  may include a first coil  114 . As shown, coil  114  may be adjacent to a first surface  106  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  (and corresponding coil  122 ) when removable case  102  is physically (and inductively) coupled to device  100 . Accordingly, coil  114  may be used to receive wireless power from device  100 . 
     Coil  122  may be capable of transmitting or receiving wireless power signals. When coil  122  is not inductively coupled to an additional coil, coil  122  may be in a standby mode. When coil  122  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  122  is in the standby mode, device  100  may intermittently check for the presence of another device (e.g., using coil  122  or another sensor in the device) adjacent to surface  108 . For example, coil  122  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  100 . The coil  122  may additionally be prepared to send a transmission (e.g., an ASK transmission) while on standby. If coil  122  receives a digital ping from another device in the system, the coil may immediately respond with the transmission. 
     When device  100  is coupled to device  102 , a magnetic sensor or other sensor in device  100  may detect the presence of accessory device  102 . The detection of the accessory device by the magnetic sensor may trigger near-field communication between device  100  and device  102 . Device  100  may use near-field communication to verify the type of accessory device  102  that is present. In this example, device  100  identifies that device  102  is a power receiving device (e.g., a device that is configured to only receive wireless power). Accordingly, device  100  may enter a power transfer mode where coil  122  transmits wireless power signals. 
     When coil  122  is used to transmit wireless power to coil  114 , inverter circuitry (e.g., inverter  86  in  FIG.  1   ) can drive the coil  122  to generate magnetic flux. Coil  114  in device  102  may be coupled to rectifier circuitry (e.g., rectifier  50  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 supercapacitor  58  in device  102 . 
     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  100 . At the same time, device  102  may siphon some of the transmitted power to also charge its supercapacitor (e.g., device  104  transmits wireless power to both devices  100  and  102 ). 
     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, (e.g., a dedicated wireless power transmitting device), or another electronic device (e.g., a wireless power transmitting and receiving device such as a charging case). An example is described herein where the power transmitting device  104  is a wireless charging puck. The wireless charging puck  104  may be connected to a wall outlet (e.g., an alternating current power source). Using power from this power source, the wireless charging puck  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  122  in device  100 . Inverter circuitry may drive the coil  126  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 . 
     While coil  126  transmits wireless power signals to coil  122  in device  100 , coil  114  in accessory  102  may siphon some of the wireless power signals. In other words, the primary wireless power transfer operation is between coil  126  and coil  122 . The power transfer operations may be performed without consideration for the presence of intervening accessory device  102 . In other words, the power transmission frequency may be selected by devices  100  and  104  based on information regarding devices  100  and  104 . Devices  100  and  104  may not factor in the presence of accessory  102  during initial handshake procedures. 
     Once devices  100  and  104  enter a power transfer phase, accessory  102  may siphon some of the power transmitted by power transmitting device  104 . Accessory device  102  may have a small thickness  110  to maximize the efficiency of power transfer from device  104  to device  100  when accessory device  102  is present. Thickness  110  (e.g., the thickness of the rear wall of the accessory) may be, for example, less than 10 millimeters, less than 8 millimeters, less than 6 millimeters, less than 4 millimeters, less than 3 millimeters, less than 2 millimeters, less than 1 millimeter, between 0.1 millimeter and 5 millimeters, etc. 
     In some scenarios, device  100  may be placed on power transmitting device  104  without an intervening accessory device  102 . A situation of this type is shown in  FIG.  6   . In this scenario, power transmitting device  104  may transmit wireless power to device  100 . Notably, the operation of devices  104  and  100  may be unchanged in  FIG.  6    relative to  FIG.  5   . In other words, device  104  transmits wireless power to device  100  in  FIG.  6    using the same procedure as in  FIG.  5   , even though the accessory is present in one scenario (in  FIG.  5   ) and absent in another scenario (in  FIG.  6   ). 
     Each one of coils  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 - 6   , 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  114 . Therefore, the magnetic alignment structures ensure proper alignment of coil  114  relative to coil  126 . When device  100  is placed on transmitter  104  without accessory device  102  present, alignment structure  128  in transmitting device  104  may magnetically couple with alignment structure  124  in device  100 . When the alignment structure  128  in device  104  is coupled to the alignment structure  124  in device  100 , the coil  126  may be aligned with the coil  122 . Therefore, the magnetic alignment structures ensure proper alignment of coil  122  relative to 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 coil  122  and coil  114 . 
     The example in  FIGS.  4  and  5    of device  102  including a first magnetic alignment structure  116  that couples to magnetic alignment structure  128  and a second magnetic alignment structure  118  that couples to magnetic alignment structure  124  is merely illustrative. Instead, device  102  may include a single magnetic alignment structure that magnetically couples to both magnetic alignment structure  128  and magnetic alignment structure  124 . 
     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  114 , alignment structure  118  and coil  114 , and alignment structure  124  and coil  122 ). 
     Each coil (e.g., coils  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. 
       FIG.  7    is a timeline showing the operations of device  100  (e.g., a cellular telephone) and device  104  (e.g., a charging puck) when the cellular telephone is placed on the charging puck. In the example of  FIG.  7   , before t 1 , the cellular telephone may be attached (e.g., physically and inductively coupled) to an accessory device such as accessory device  102 . In this example, coil  122  of device  100  is in a power transmitting mode and transmits wireless power to coil  114  in accessory device  102 . 
     When device  100  and an attached removable accessory  102  are placed on charging puck  104 , it is desirable for device  100  (and accessory device  102 ) to obtain wireless power from puck  104 . However, while device  100  is transmitting wireless power to accessory device  102 , a technique is needed for device  100  to detect the presence of charging puck  104 . In some embodiments, to allow device  100  to transfer sufficient wireless power to accessory  102  while still ensuring device  100  is capable of detecting attachment to device  104 , device  100  transmits alternating-current wireless power signals in bursts. 
     As shown in  FIG.  7   , the cellular telephone  100  transmits wireless power in a transmitting burst period between t 1  and t 2 . Between t 1  and t 2 , inverter circuitry (e.g., inverter  86  in  FIG.  1   ) can drive the coil  122  in device  100  to generate alternating-current wireless power signals (e.g., at a frequency between 100 kHz and 400 kHz). The cellular telephone  100  ceases transmitting the alternating-current wireless power signals at t 2  and enters a sleep period between t 2  and t 5 . Between t 2  and t 3 , coil  122  is in a sleep period (sometimes referred to as standby period) during which the coil does not transmit alternating-current wireless power signals. While in the sleep period, device  100  may monitor for communications from/the presence of charging puck  104  (e.g., using coil  122  and/or additional sensors/components in device  100 ). 
     While attached to the accessory  102  (and not charging puck  104 ), cellular telephone  100  may continuously cycle (alternate) between the power transmitting burst periods (in which the coil transmits AC wireless power signals) and the sleep periods (in which the coil does not transmit AC wireless power signals). Before t 1  in  FIG.  7   , cellular telephone  100  may have repeatedly switched between power transmitting burst periods and sleep periods. As shown in  FIG.  7   , after the sleep period concludes at t 5 , another power transmitting burst period occurs between t 5  and t 7 . At t 7 , the cellular telephone switches back to a sleep period. 
     The duration  134  of the burst period may be less than the duration  136  of the sleep period in each cycle. In general, durations  134  and  136  may have any desired magnitudes. Duration  134  may be less than 300 milliseconds, less than 200 milliseconds, less than 100 milliseconds, less than 50 milliseconds, greater than 300 milliseconds, greater than 200 milliseconds, greater than 100 milliseconds, greater than 50 milliseconds, etc. Duration  136  may be less than 1000 milliseconds, less than 500 milliseconds, less than 300 milliseconds, less than 200 milliseconds, less than 100 milliseconds, less than 50 milliseconds, greater than 1000 milliseconds, greater than 500 milliseconds, greater than 300 milliseconds, greater than 200 milliseconds, greater than 100 milliseconds, greater than 50 milliseconds, etc. 
     The magnitude of duration  134  relative to the total time of the cycle (e.g., the sum of magnitudes  134  and  136 ) may be referred to as the duty cycle of the wireless power transmitting mode (e.g., the percentage of time AC signals are transmitted in each cycle). The duty cycle may be less than 100%, less than 80%, less than 60%, less than 40%, less than 20%, less than 10%, greater than 60%, greater than 40%, greater than 20%, greater than 10%, greater than 5%, etc. 
     It should be understood that, during each burst period, the coil transmits alternating-current wireless power signals that also have a respective duty cycle. The duty cycle of the transmitted AC wireless power signals may be less than 90%, less than 75%, less than 50%, less than 30%, greater than 10%, greater than 30%, greater than 50%, etc. 
     The magnitudes of durations  134  and  136  may be tuned based on the conditions within the wireless power system. In particular, if the accessory device has a higher load (and therefore consumes more power), duration  134  may be higher and if the accessory device has a lower load (and therefore consumes less power), duration  134  may be lower. Similarly, the duration  136  may be increased if the accessory device has a lower load and decreased in the accessory device has a higher load. 
     Before t 8 , the cellular telephone and mated accessory device are not attached to the charging puck. During this time, charging puck  104  intermittently transmits low power pings (sometimes referred to as analog pings) in order to monitor for the presence of a device on the charging puck. During each low power ping, a test pulse is applied to the transmitter coil  126 . The voltage of coil  126  may be monitored when the test pulse is applied to transmitter coil  126 . A deviation in coil voltage from a nominal standby value may indicated a device is present on charging puck  104 . 
     As shown in  FIG.  7   , charging puck  104  may emit a low power ping at t 1 , t 2 , t 3 , t 4 , and t 6 . The charging puck does not detect any placed objects during this time period (e.g., before t 8 ) and therefore emits the low power pings at a regular interval. The interval  138  between each low power ping may be less than 5 seconds, less than 1000 milliseconds, less than 500 milliseconds, less than 300 milliseconds, less than 200 milliseconds, less than 100 milliseconds, less than 50 milliseconds, greater than 1000 milliseconds, greater than 500 milliseconds, greater than 300 milliseconds, greater than 200 milliseconds, greater than 100 milliseconds, greater than 50 milliseconds, etc. 
     At t 8 , cellular telephone  100  (with mated accessory device  102 ) is placed on charging puck  104 , and it is desirable for cellular telephone  100  to switch from the power transmitting mode to a power receiving mode. After attachment between the charging puck and the cellular telephone (and mated accessory device), charging puck  104  transmits a low power ping at t 9  according to the regular interval  138 . Because the cellular telephone is present on the charging puck, charging puck  104  may detect the presence of an object on the mat during the low power ping. To verify the presence of an object on the mat, charging puck may transmit additional low power pings between t 9  and t 10 . After the charging puck is confident that a device capable of receiving wireless power has been placed on the charging puck, the charging puck enters a handshake phase at t 10 . During the handshake phase, the devices negotiate a frequency and/or rate of power delivery. After the handshake phase (and associated power delivery negotiation) is complete, the devices enter a dedicated power delivery phase using the agreed upon power delivery parameters. 
     During the handshake phase, low-level wireless power signals may be transmitted from the wireless power transmitting device (e.g., digital ping operations may be performed). During the handshake phase, sufficient power is supplied to power communications circuitry in the wireless power receiving device. The wireless power signals provided during the handshake phase (e.g., digital pings) may include longer pulses than the analog pings at t 1 , t 2 , t 3 , etc. Additionally, the wireless power signals in the handshake phase provide sufficient power to activate the power receiving device  100  (if one is indeed present). By powering the control circuitry and its associated communications circuitry in device  104 , devices  100  and  104  can subsequently negotiate over a wireless link (e.g., an in-band link) to determine an appropriate wireless power transfer level for system  8  to use during subsequent wireless power transfer operations (e.g., a significantly larger power such as 5 W, 10 W, or other relatively large value associated with normal wireless power transmission operations, which is generally at least 5 times, at least 10 times, or at least 25 times greater than the power used during the handshake phase). 
     Also at t 10 , upon initiation of the handshake phase by charging puck  104 , cellular telephone  100  enters a wireless power receiving mode. Cellular telephone  100  stops transmitting wireless power to the accessory device and instead receives wireless power from the charging puck. 
     The magnitude of durations  136  and  138  may be selected to ensure that the sleep periods of the cellular telephone is sufficiently long to guarantee overlap with a low power ping and subsequent initiation of handshake proceedings from the charging puck  104 . In other words, there is a duration  140  between the last low power ping (at t 6 ) before attachment (at t 8 ) and the initiation of the handshake procedure at t 10  after the charging puck is attached to the cellular telephone and detects the presence of a device. To ensure that cellular telephone  100  is in a sleep period when the handshake phase commences (and, therefore, the cellular telephone is capable of communicating in order to negotiate power transfer parameters), duration  140  may be shorter than duration  136  of the sleep period. This prevents a scenario where cellular telephone does not detect the handshake initiation at t 10  and undesirably stays in the power transmitting mode (even though the cellular telephone is on a wireless charging puck). Duration  138  may also be shorter than duration  136 . 
     Although not explicitly shown in  FIG.  7   , the accessory device may remain in a wireless power receiving mode throughout the operations of  FIG.  7   . Before the cellular telephone is placed on the charging puck, the accessory device is attached to the cellular telephone and receives wireless power from the cellular phone during the power transmission bursts (e.g., between t 1  and t 2  and between t 5  and t 7 ). While the cellular telephone is in the sleep periods, the accessory device does not receive wireless power from the cellular telephone and instead uses stored power (e.g., from a supercapacitor) to operate. After the cellular telephone (and mated accessory) are placed on the charging puck, the cellular telephone switches to a power receiving mode and receives wireless power from the charging puck. The accessory device remains in the receiving mode throughout this process. When the charging puck delivers wireless power to the cellular telephone, the accessory device may siphon some of the wireless power and use the siphoned power to operate and/or charge a power storage device in the accessory. 
     Notably, the operations of charging puck  104  are not impacted by the presence of accessory device  102 . In other words, the timeline in  FIG.  7    for charging puck  104  is the same whether a cellular telephone and mated (intervening) accessory are attached to the charging puck or only a cellular telephone (without a mated accessory) is attached to the charging puck. 
       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  202  in which coil  122  receives wireless power (e.g., from coil  126  in power transmitting device  104 , from a coil in a removable accessory, etc.). In the receiving mode, rectifier circuitry in device  100  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 power transmitting device  104 . In some arrangements, device  100  may operate in the receiving mode while inductively coupled to an accessory device that is capable of transmitting wireless power. For example, device  100  may be inductively coupled to a battery case that includes a battery and a wireless power coil. Device  100  may receive wireless power from the battery case while inductively coupled to the battery case. 
     Device  100  may also be operable in a transmitting mode  204  in which coil  122  transmits wireless power. Device  100  may transmit wireless power to an accessory device such as accessory 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 . 
     In the transmitting mode, device  100  may transmit wireless power in bursts that are separated by sleep periods where wireless power is not transmitted. During the wireless power transmission bursts, 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 . During the sleep periods between bursts, device  100  does not transmit AC wireless power signals and monitors for digital pings from a power transmitting device such as charging puck  104 . 
     Device  100  may operate in the transmitting mode while device  100  is inductively coupled to removable accessory  102  (that is a dedicated power receiving device). In some cases, device  100  may be coupled to an accessory that is a wireless power transmitting and receiving device (such as a battery pack). Device  100  may also operate in the transmitting mode (and transmit wireless power to the battery pack) while device  100  is tethered to mains power through a power cable and a voltage converter such as an AC to USB adapter. 
     Device  100  may switch from the receiving mode to the transmitting mode in response to the cellular telephone (and a mated accessory device) being removed from a power transmitting device. 
     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  204 . 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 the mode of device  100  while device is inductively coupled to removable accessory  102 . 
       FIG.  9    is a flowchart of illustrative operations performed by a cellular telephone in a wireless power system. As shown in  FIG.  9   , the cellular telephone (e.g., device  100 ) may detect the presence of an additional device at step  302 . To detect the additional device, the cellular telephone may use a sensor that is sensitive to electromagnetism such as a Hall effect sensor (a sensor that measures the magnitude of a magnetic field). This example is merely illustrative. An accelerometer (e.g., that detects when the cellular telephone bumps into an additional device) or the wireless power coil itself (e.g., coil  122  that is also used to transmit or receive wireless power) may be used to detect the presence of an additional device. In general, input from any subset (e.g., one or more) of the input-output components in device  100  may be used to detect the presence of the additional device. 
     Once the additional device is detected, cellular telephone  100  may optionally initiate an NFC scan during step  304 . NFC communication may be used to identify the device type of the additional device (e.g., a removable accessory that only receives wireless power, a removable accessory that transmits or receives wireless power, etc.) and/or obtain other information from the additional device. 
     In response to determining that the additional device is an accessory device  102  that only receives wireless power, cellular telephone  100  may enter a power transmitting mode in step  306 . In the power transmitting mode, coil  122  transmits wireless power in bursts to the accessory device. Also at step  306 , out-of-band communications (e.g., Bluetooth communications using antennas formed separately from coils  114  and  122 ) may be initiated between cellular telephone  100  and accessory device  102 . Cellular telephone  100  may continue to transmit wireless power to the accessory device while the cellular telephone is attached to the accessory device. 
       FIG.  10    is a flowchart of illustrative operations performed by a cellular telephone in a wireless power system when the cellular telephone switches from a power transmitting mode to a power receiving mode. At the beginning of step  402 , the cellular telephone  100  is physically attached and inductively coupled to accessory device  102  (e.g., as described at the end of step  306  in  FIG.  9   ). Cellular telephone  100  is in a power transmitting mode (e.g., mode  204  in  FIG.  8   ) in which wireless power is transmitted in bursts to the accessory device. During step  402 , the cellular telephone is attached to a wireless power transmitting device such as charging puck  104 . 
     Next, at step  404 , the cellular telephone receives a digital ping from the wireless power transmitting device. The cellular telephone may receive the digital ping while the cellular telephone is in a sleep period between power transmission bursts (as shown and discussed in connection with  FIG.  7   ). Accordingly, the cellular telephone is capable of detecting the digital ping and entering a handshake procedure with the power transmitting device. In response to detecting the digital ping, the cellular telephone switches from the power transmitting mode to the power receiving mode at step  406 . In the power receiving mode, the cellular telephone concludes handshake procedures with the power transmitting device and commences a power transfer phase where the cellular telephone receives wireless power from the power transmitting device. 
     While the cellular telephone and accessory device are present on the charging puck, the cellular telephone may receive wireless power form the charging puck. The accessory device may also receive wireless power from the charging puck (e.g., by siphoning power transmitted from the charging puck). At some subsequent point, the cellular telephone may detect a drop in rectifier voltage indicating that the cellular telephone (and mated accessory device) has been removed from the charging puck. In response to determining that the cellular telephone (and mated accessory device) has been removed from the charging puck, the cellular telephone may revert back to the power transmitting mode and transmit bursts of wireless power to the accessory device. 
     In another scenario, the cellular telephone may become fully charged and thereafter cease receiving wireless power from the power transmitting device  104  (even though the cellular telephone is still present on the power transmitting device). However, in some scenarios, the cellular telephone may be fully charged before accessory device  102  or accessory device  102  may lose charge faster than the cellular telephone. This may result in accessory device  102  having an undesirably low charge (because it is not receiving any wireless power due to cellular telephone  100  not requiring power from charging puck  104 ). To prevent this type of scenario and ensure accessory device  102  has sufficient charge, cellular telephone  100  (which knows it is mated to accessory device  102 ) may negotiate a short duration between low power pings from charging puck  104 . 
     Even if cellular telephone  100  is fully charged and does not need dedicated power transfer from charging puck  104 , charging puck  104  may intermittently transmit low power pings to cellular telephone to determine if cellular telephone  100  needs to resume power transfer operations. If the duration between these pings is short, the pings may provide sufficient power to charge accessory device  102  (which siphons some of the power from the low power pings). The low power pings from charging puck  104  emulate the transmitting bursts used by cellular telephone  100  when charging 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: 20211028
Publication Date: 20240924
Grant Date: 20240924
Priority Date: 20210823
Inventors: SHI, LIXIN
QIU, WEIHONG
XU, Zelin
MOUSSAOUI, ZAKI
CHABALKO, MATTHEW J.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 85228083