PATENT DOCUMENT

Publication Number: US-12119675-B2
Application Number: US-202217834180-A
Country: US
Kind Code: B2

Title: Feedback control schemes for wireless power transfer circuits

Abstract:
Portable electronic devices such as cellular telephones, wristwatch devices, tablet computers, wireless earbuds, and other portable devices use batteries. The batteries in these devices may be charged using a wireless power system. For example, a user may place devices such as tablet computers and cellular telephones on a wireless charging puck or mat to wirelessly charge these devices. Wireless power systems include a power transmitting device and a power receiving device. Coils in the power transmitting and receiving devices are used to transmit and receive wireless power signals. The coupling between the transmitting and receiving coils may affect the wireless charging efficiency and the power produced in the receiving device. Disclosed herein are feedback control schemes to optimize efficiency of wireless power transfer systems.

Claims:
What is claimed: 
     
       1. A wireless power receiving device configured to receive wireless power signals from a wireless power transmitting device, the wireless power receiving device comprising:
 a wireless power transfer coil; 
 rectifier circuitry coupled to the wireless power transfer coil and configured to rectify signals from the wireless power transfer coil into a rectifier output voltage; and 
 control circuitry configured to:
 regulate the rectifier output voltage at a target rectifier output voltage level; 
 receive, from the wireless power transmitting device, a status message indicative of an inverter input voltage of the wireless power transmitting device; 
 determine, based on the status message received from the wireless power transmitting device, whether the inverter input voltage is at a maximum inverter input voltage level; and 
 adjust the target rectifier output voltage level based on the status message indicative of the inverter input voltage, wherein in accordance with determining the inverter input voltage is at the maximum inverter input voltage level, the control circuitry:
 measures a present rectifier output voltage value; and 
 compares the present rectifier output voltage value with a minimum fold back voltage level,
 wherein in accordance with determining the present rectifier output voltage value is less than or equal to the minimum fold back voltage level, the control circuitry sets a new target rectifier output voltage level to the minimum fold back voltage level; and 
 
 regulates the rectifier output voltage at the new target rectifier output voltage level. 
 
 
 
     
     
       2. The wireless power receiving device of  claim 1 , wherein in accordance with determining the present rectifier output voltage value is greater than the minimum fold back voltage level, the control circuitry:
 sets the new target rectifier output voltage level to the present rectifier output voltage value; and 
 regulates the rectifier output voltage at the new target rectifier output voltage level. 
 
     
     
       3. The wireless power receiving device of  claim 1 , wherein in accordance with determining the present rectifier output voltage value is greater than the minimum fold back voltage level, the control circuitry compares the present rectifier output voltage value with the target rectifier output voltage level. 
     
     
       4. The wireless power receiving device of  claim 3 , wherein in accordance with determining the present rectifier output voltage value is less than the target rectifier output voltage level, the control circuitry transmits a Control Error Packet (CEP) to the wireless power transmitting device to ask for more power. 
     
     
       5. The wireless power receiving device of  claim 1 , wherein the control circuitry determines from the status message that the inverter input voltage is not at the maximum inverter input voltage level, the control circuitry:
 regulates the rectifier output voltage at the target rectifier output voltage level. 
 
     
     
       6. A wireless power receiving device configured to receive wireless power signals from a wireless power transmitting device, the wireless power receiving device comprising:
 a wireless power transfer coil; 
 rectifier circuitry coupled to the wireless power transfer coil and configured to rectify signals from the wireless power transfer coil into a rectifier output voltage; and 
 control circuitry configured to:
 receive, from the wireless power transmitting device, a status message indicative of an inverter input voltage of the wireless power transmitting device; 
 determine, based on the status message received from the wireless power transmitting device, whether the inverter input voltage is at a maximum inverter input voltage level, 
 wherein in accordance with determining the inverter input voltage is not at the maximum inverter input voltage level, the control circuitry:
 measures a characteristic of the rectifier circuitry; 
 determines a target rectifier output voltage level based on the measured characteristic of the rectifier circuitry; and 
 dynamically regulates the rectifier output voltage at the target rectifier output voltage level; 
 
 wherein in accordance with determining if the inverter input voltage is at the maximum inverter input voltage level, the control circuitry:
 measures a present rectifier output voltage value; 
 compares the present rectifier output voltage value with a minimum fold back voltage level,
 wherein in accordance with determining the present rectifier output voltage value is less than or equal to the minimum fold back voltage level, the control circuitry sets a new target rectifier output voltage level to the minimum fold back voltage level; and 
 
 regulates the rectifier output voltage at the new target rectifier output voltage level. 
 
 
 
     
     
       7. The wireless power receiving device of  claim 6 , wherein the characteristic of the rectifier circuitry comprises one of a rectifier output power and a rectifier output current. 
     
     
       8. The wireless power receiving device of  claim 6 , wherein in accordance with determining the present rectifier output voltage value is greater than the minimum fold back voltage level,
 sets the new target rectifier output voltage level to the present rectifier output voltage value; and 
 regulates the rectifier output voltage at the new target rectifier output voltage level. 
 
     
     
       9. The wireless power receiving device of  claim 6 , wherein in accordance with determining the present rectifier output voltage value is greater than the minimum fold back voltage level, the control circuitry:
 measures the characteristic of the rectifier circuitry; 
 determines the target rectifier output voltage level based on the measured characteristic of the rectifier circuitry; and 
 compares the present rectifier output voltage value with the target rectifier output voltage level. 
 
     
     
       10. The wireless power receiving device of  claim 9 , wherein the control circuitry determines the present rectifier output voltage value is less than the target rectifier output voltage level, the control circuitry transmits a Control Error Packet (CEP) to the wireless power transmitting device to ask for more power. 
     
     
       11. A wireless power receiving device configured to receive wireless power signals from a wireless power transmitting device, the wireless power receiving device comprising:
 a wireless power transfer coil; 
 rectifier circuitry coupled to the wireless power transfer coil and configured to rectify signals from the wireless power transfer coil into a rectifier output voltage; and 
 control circuitry configured to:
 ask the wireless power transmitting device for information indicative of an operating condition of an inverter of the wireless power transmitting device, wherein the wireless power transfer coil is receiving wireless power signals transmitted by the wireless power transmitting device using the inverter; 
 wherein the information comprises a status message indicative of whether the inverter of the wireless power transmitting device is operating at a maximum input voltage level; 
 wherein in accordance with determining the inverter input voltage is not at the maximum inverter input voltage level, the control circuitry:
 regulates the rectifier output voltage at a target rectifier output voltage level; 
 
 wherein in accordance with determining the inverter input voltage is at the maximum inverter input voltage level, the control circuitry:
 measures a present rectifier output voltage value; 
 compares the present rectifier output voltage value with a minimum fold back voltage level,
 wherein in accordance with determining the present rectifier output voltage value is less than or equal to the minimum fold back voltage level, the control circuitry sets a new target rectifier output voltage level to the minimum fold back voltage level; and 
 
 regulates the rectifier output voltage at the new target rectifier output voltage level. 
 
 
 
     
     
       12. The wireless power receiving device of  claim 11 , wherein in accordance with determining the present rectifier output voltage value is greater than the minimum fold back voltage level, the control circuitry:
 sets the new target rectifier output voltage level to the present rectifier output voltage value; and 
 regulates the rectifier output voltage at the new target rectifier output voltage level.

Description:
PRIORITY 
     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 63/212,252, entitled “FEEDBACK CONTROL SCHEMES FOR WIRELESS POWER TRANSFER CIRCUITS,” filed on Jun. 18, 2021, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL BACKGROUND 
     The present disclosure relates generally to wireless charging, and more particularly, to feedback control schemes for wireless power transfer in wireless power systems. 
     BACKGROUND 
     Portable electronic devices such as cellular telephones, wristwatch devices, tablet computers, wireless earbuds, and other portable devices use batteries. The batteries in these devices may be charged using a battery charging system. To enhance convenience for users, wireless power systems have been provided that allow batteries in portable electronic devices to be charged wirelessly. Coils in power transmitting and receiving devices may be used to transmit and receive wireless power signals. The coupling between the transmitting and receiving coils may affect the wireless charging efficiency and the power produced in the receiving device. 
     The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the innovations described herein. Thus, the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use with the innovations described herein, nor is it intended to indicate that any element is essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims. 
     SUMMARY 
     Wireless power systems include a power transmitting device and a power receiving device. Coils in the power transmitting and receiving devices are used to transmit and receive wireless power signals. The coupling between the transmitting and receiving coils may affect the wireless charging efficiency and the power produced in the receiving device. 
     An exemplary wireless power receiving device may be configured to receive wireless power signals from a wireless power transmitting device. The wireless power receiving device may include a wireless power transfer coil. In addition, the receiving device includes rectifier circuitry coupled to the wireless power transfer coil and configured to rectify signals from the wireless power transfer coil into output voltage. The receiving device also includes control circuitry that is configured to regulate the rectifier output voltage at a target rectifier output voltage level, receive from the wireless power transmitting device, a status message indicative of an inverter input voltage, and adjust the target output voltage based on the status of the inverter input voltage. 
     Another exemplary wireless power receiving device may be configured to receive wireless power signals from a wireless power transmitting device. The wireless power receiving device may include a wireless power transfer coil. In addition, the receiving device includes rectifier circuitry coupled to the wireless power transfer coil and configured to rectify signals from the wireless power transfer coil into output voltage. The receiving device also includes control circuitry that is configured to measure a characteristic of the rectifier circuitry, determine a target rectifier output voltage level based on the measured characteristic of the rectifier circuitry, and dynamically regulate the rectifier output voltage at the target rectifier output voltage level. 
     Another exemplary wireless power receiving device may be configured to receive wireless power signals from a wireless power transmitting device. The wireless power receiving device may include a wireless power transfer coil. In addition, the receiving device includes rectifier circuitry coupled to the wireless power transfer coil and configured to rectify signals from the wireless power transfer coil into output voltage. The receiving device also includes control circuitry that is configured to regulate the rectifier output voltage at a target rectifier output voltage level. The control circuitry may also ask the wireless power transmitting device for information indicative of an operating condition of an inverter of the wireless power transmitting device, wherein the wireless power transfer coil is receiving wireless power signals transmitted by the wireless power transmitting device using the inverter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary and following detailed description are better understood when read in conjunction with the appended drawings. In the drawings, for purposes of explanation, numerous specific details are set forth in order to provide an understanding of the variations in implementing the disclosed technology. However, the instant disclosure may take many different forms and should not be construed as limited to the specific examples disclosed in the drawings. When practical, like numbers refer to like elements throughout. In the drawings: 
         FIG.  1    is a schematic diagram of an illustrative wireless power system in accordance with an aspect of the present disclosure. 
         FIG.  2    is an exploded view of an illustrative wireless power receiving device with a coil for receiving wireless power in accordance with an aspect of the present disclosure. 
         FIG.  3 A  is a perspective view of an illustrative wireless power transmitting device having a coil for charging wireless power receiving coils in accordance with an aspect of the present disclosure. 
         FIG.  3 B  is a top view of the wireless power transmitting device in  FIG.  3 A . 
         FIG.  4    is an illustrative plot of a prior art control method for wireless power transfer between power transmitting and receiving devices in the wireless power system shown in  FIG.  1   . 
         FIG.  5    is an illustrative plot of a feedback control scheme for a wireless power transfer system according to an aspect of the present disclosure. 
         FIG.  6    is an illustrative plot of another feedback control scheme for a wireless power transfer system according to an aspect of the present disclosure. 
         FIG.  7    is a flow diagram of an exemplary control loop algorithm implemented in the power receiving device of a wireless power transfer system using feedback control schemes illustrated in  FIGS.  5  and  6   . 
     
    
    
     DETAILED DESCRIPTION 
     Portable electronic devices such as cellular telephones, wristwatch devices, tablet computers, wireless earbuds, and other portable devices use batteries. The batteries in these devices may be charged using a wireless charging system. For example, a user may place devices such as wristwatch devices and cellular telephones on a wireless charging mat to wirelessly charge these devices. 
     An illustrative wireless power system is shown in  FIG.  1   . Wireless power system  8  includes electronic devices  10 . Electronic devices  10  include electronic devices that transmit wireless power and/or electronic devices that receive wireless power. Because battery charging is a common use of received power, wireless power transfer operations in system  8  are sometimes referred to as battery charging operations. However, power may also be provided to a receiving device to operate a display or other circuitry in the receiving device without battery charging, if desired. Accordingly, the wireless power may be used for charging batteries in electronic devices and in supplying power to other device components. 
     Charging may be performed by wirelessly transferring power (e.g., using inductive charging) from a power transmitting device such as device  12  to a power receiving device such as device  24 . Coils in the power transmitting and receiving devices may be used to transmit and receive wireless power signals. In the example of  FIG.  1   , power is being transferred wirelessly using wireless power signals  44 . The wireless charging efficiency of device  24  is affected, in part, by the coupling between coil  42  on device  12  and coil  48  on device  24  (also referred to herein as the coupling between transmitting device  12  and receiving device  24 ). 
     The physical alignment of coils  42  and  48  in the X, Y, and Z dimensions affects the electromagnetic coupling. An offset of x=0, y=0 means the centers of coils  42  and  48  are aligned in the X-Y plane. An offset of z=0 may mean the distance between the surfaces of the two devices containing coils  42  and  48  is at a minimum distance. For example, neither the power transmitting device  12  nor the power receiving device  24  has a case that separates the two devices. An offset of (x, y, z)=(0, 0, 0) may be referred to as a best coupling condition. In addition, an offset of (r, z)=(0, 0), where “r” is the radius of offset between the centers of coil  42  and coil  48 , may also be referred to as a best coupling condition. 
     The electromagnetic coupling between coil  42  on device  12  and coil  48  on device  24  may be designed to operate across a positional tolerance range. In one example, the wireless power transfer system may be optimized for the centers of coils  42  and  48  to be aligned within 5 mm in the X-Y plane and the distance between surfaces of devices  12  and  24  to be within 5 mm in the Z direction. Such design criteria may be referred to as a “5 mm by 5 mm” offset. In this example, a “good” coupling would occur when the center of coil  48  of power receiving device  24  is aligned within 5 mm by 5 mm of center of coil  42  of the power transmitting device  12 . In such an orientation, good charging may result because the system is designed to transmit full power from device  12  to device  24  when the coils are offset by +/−5 mm. Continuing with the 5 mm-by-5 mm design example, a coupling where the power transmitting and receiving coils are offset by more than the +/−5 mm design criteria may be classified as a “bad” coupling. A person of skill in the art will recognize that the wireless power transfer system is not limited by this exemplary positional tolerance range and may be designed for alternative ranges (e.g., +/−1 mm, +/−2 mm, +/−3 mm, +/−4 mm, +/−6 or more, etc.) without departing from the scope and spirit of the invention as described herein. 
     A good coupling between the transmitting and receiving coils may promote efficient wireless power transfer. A bad coupling between the transmitting and receiving coils may negatively affect the wireless charging efficiency and the power produced in receiving device  24 . Disclosed herein are feedback control schemes to optimize efficiency of wireless power transfer systems. 
     During operation of system  8 , wireless power transmitting device  12  wirelessly transmits power to one or more wireless power receiving devices such as device  24 . The wireless power receiving devices may include electronic devices such as wristwatches, cellular telephones, tablet computers, laptop computers, ear buds, battery cases for ear buds and other devices, tablet computer pencils (e.g., styluses) and other input-output devices (e.g., accessory devices), wearable devices, or other electronic equipment. The wireless power transmitting device may be an electronic device such as a wireless charging puck or mat that has a charging surface (e.g., a planar charging surface) that receives portable devices to be charged, a tablet computer or other portable electronic device with wireless power transmitting circuitry (e.g., one of devices  24  that has wireless power transmitting circuitry), or other wireless power transmitting device. The wireless power receiving devices use power from the wireless power transmitting device for powering internal components and for charging internal batteries. 
     As shown in  FIG.  1   , wireless power transmitting device  12  includes control circuitry  16 . Wireless power receiving device  24  includes control circuitry  30 . Control circuitry in system  8  such as control circuitry  16  and control circuitry  30  (and/or control circuitry in other devices  10 ) 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  and  24 . For example, the processing circuitry may be used in operating the control loops discussed herein, selecting coils, adjusting the phases and magnitudes of coil drive signals, determining power transmission levels, processing sensor data and other data, processing user input, handling negotiations between devices  12  and  24 , sending and receiving in-band and out-of-band data, making measurements, starting and stopping charging operations, turning devices  10  on and off, placing devices  10  in low-power sleep modes, 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 devices  10  (e.g., control circuitry  16  and/or  30 ). 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 puck or mat that includes power adapter circuitry), may be a wireless charging puck or mat that is coupled to a power adapter or other equipment by a cable, may be a portable electronic device (cellular telephone, tablet computer, laptop computer, etc.), may be equipment that has been incorporated into furniture, a vehicle, or other system, or may be other wireless power transfer equipment. Illustrative configurations in which wireless power transmitting device  12  is a wireless charging puck, mat, or portable electronic device 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, a tablet computer input device such as a wireless tablet computer pencil, a battery case, or other electronic equipment. Power transmitting device  12  may be coupled to a wall outlet (e.g., an alternating current power source), may have a battery 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. In some configurations, AC-DC power converter  14  may be provided in an enclosure (e.g., a power brick enclosure) that is separate from the enclosure of device  12  (e.g., a wireless charging mat enclosure or portable electronic device enclosure) and a cable may be used to couple DC power from the power converter to device  12 . DC power may be used to power control circuitry  16 . 
     During operation, a controller in control circuitry  16  may use power transmitting circuitry  52  to transmit wireless power to power receiving circuitry  54  of device  24 . Power transmitting circuitry  52  may have switching circuitry (e.g., inverter circuitry  60  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 transmit coils  42 . Coils  42  may be arranged in a planar coil array, such as in configurations in which device  12  is a wireless charging mat, or may be arranged in other configurations. In some arrangements, device  12  may have a single coil. In arrangements in which device  12  has multiple coils, the coils may be arranged in one or more layers. Coils in different layers may or may not overlap with each other. 
     As the AC currents pass through one or more coils  42 , a time varying electromagnetic (e.g., magnetic) field (signals  44 ) is produced that is received by one or more corresponding receiver coils such as coil  48  in power receiving device  24 . When the time varying electromagnetic field is received by coil  48 , corresponding alternating-current currents are induced in coil  48 . Rectifier circuitry such as rectifier  50 , which contains rectifying components such as synchronous rectification metal-oxide-semiconductor transistors arranged in a bridge network, converts received AC signals from coil  48  into DC voltage signals for powering device  24 . 
     The DC voltages produced by rectifier  50  may be used in powering (charging) an energy storage device such as battery  58  and may be used in powering other components in device  24 . For example, device  24  may include input-output devices  56  such as a display, touch sensor, communications circuits, audio components, sensors, components that produce electromagnetic signals that are sensed by a touch sensor in a tablet computer or other device with a touch sensor (e.g., to provide pencil input, etc.), and other components and these components may be powered by the DC voltages produced by rectifier  50  (and/or DC voltages produced by battery  58  or other energy storage device in device  24 ). 
     Device  12  and/or device  24  may communicate wirelessly (e.g., using in-band and out-of-band communications). Device  12  may, for example, have wireless transceiver (TX/RX) circuitry  40  that wirelessly transmits out-of-band signals to device  24  using an antenna. Wireless transceiver circuitry  40  may be used to wirelessly receive out-of-band signals from device  24  using the antenna. Device  24  may have wireless transceiver circuitry  46  that transmits out-of-band signals to device  12 . Receiver circuitry in wireless transceiver  46  may use an antenna to receive out-of-band signals from device  12 . In some configurations, devices  10  may communicate through local area networks and/or wide area networks (e.g., the internet). 
     Wireless transceiver circuitry  40  may use one or more coils  42  to transmit in-band signals to wireless transceiver circuitry  46  that are received by wireless transceiver circuitry  46  using coil  48 . Any suitable modulation scheme may be used to support in-band communications between device  12  and device  24 . With one illustrative configuration, frequency-shift keying (FSK) is used to convey in-band data from device  12  to device  24  and amplitude-shift keying (ASK) is used to convey in-band data from device  24  to device  12 . Power may be conveyed wirelessly from device  12  to device  24  during these FSK and ASK transmissions. Other types of in-band communications may be used, if desired. 
     During wireless power transmission operations, circuitry  52  supplies AC drive signals to one or more coils  42  at a given power transmission frequency. The power transmission frequency may be, for example, a predetermined frequency of about 125 kilohertz (kHz), at least 80 kHz, at least 100 kHz, less than 500 kHz, less than 300 kHz, less than 150 KHz, between 80 kHz and 150 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. 
     During wireless power transfer operations, while power transmitting circuitry  52  is driving AC signals into one or more of coils  42  to produce electromagnetic signals  44  at the power transmission frequency, wireless transceiver circuitry  40  may use FSK modulation to transmit data and information over the driving AC signals  44 . In device  24 , coil  48  is used to receive electromagnetic 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  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  42  and  48  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . Other types of in-band communications between device  12  and device  24  may be used, if desired. 
     In-band communications between device  24  and device  12  may use ASK modulation and demodulation techniques or other suitable in-band communications 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)  42 . Wireless transceiver circuitry  40  monitors the amplitude of the AC signal passing through coil(s)  42  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 a stream of ASK data bits (e.g., a series of ASK data packets) to be transmitted in-band from device  24  to device  12  with coils  48  and  42  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . 
     Control circuitry  16  may have external object measurement circuitry  41  (sometimes referred to as foreign object detection circuitry or external object detection circuitry) that detects external objects on a charging surface associated with device  12 . Circuitry  41  may detect foreign objects such as coils, paper clips, and other metallic objects and may detect the presence of wireless power receiving devices  24 . During object detection and characterization operations, external object measurement circuitry  41  may be used to make measurements on coils  42  to determine whether any devices  24  are present on device  12  (e.g., whether devices  24  are suspected to be present on device  12 ). Measurement circuitry  43  in control circuitry  30  may be used in making current and voltage measurements in coil  48 , and/or may be used in making other measurements on wireless power receiving circuitry  54 . Measurement circuitry  41  in control circuitry  16  may be used in making current and voltage measurements in coil(s)  42 , and/or may be used in making other measurements on wireless power transmitting circuitry  52 . In scenarios where device  12  includes multiple coils  42 , control circuitry  16  may perform measurements using each coil  42  in sequence and/or in parallel. Control circuitry  16  may compare measurements made using measurement circuitry  41  to predetermined characteristics associated with device  24  (e.g., predetermined characteristics associated with different types of devices  24  that control circuitry  16  uses to identify the type of device  24  that is being charged). 
       FIG.  2    illustrates an exploded view of an exemplary wireless power receiving device  24 . As shown in  FIG.  2   , wireless power receiving device  24  includes a housing such as a top housing  62  and a bottom housing  64  that can mate to define an interior cavity. Bottom housing  64  has a surface  74 , also referred to herein as rear surface  74 , that is placed on or over a charging surface of device  12  for wirelessly charging device  24 . For example, both rear surface  74  and the charging surface  82  of device  12  may lie substantially parallel to the X-Y plane of  FIG.  2    during wireless charging. A display screen (e.g., OLED display) or other input-output devices may be mounted to top housing  64  on surface  72 , also referred to herein as upper surface  74 . 
     Device  24  includes one or more coils  48  on the bottom housing  64  or within the interior cavity formed by the top housing  62  and the bottom housing  64 . Housing  62 ,  64  may include metal materials, dielectric materials, or combinations of these and/or other materials. Device  24  may optionally include a ferromagnetic shield  66  and a thermal shield  65  in the vicinity of the coil  48 . The thermal shield  65  may include a graphite or similar layer that provides thermal isolation between coil  48  and the battery and other components of the device  24 . The ferromagnetic shield  66  may be positioned between the power coil  48  and the thermal shield  65 . The ferromagnetic shield  66  may act as a magnetic field shield for redirecting magnetic flux to get higher coupling with coil  42  in the power transmitting device  12 , which may result in improved charging efficiency. The device  24  may optionally include an adhesive component  67  that attaches coil  48  to bottom housing  64 . The adhesive component  67  may be a single sheet of an adhesive material, such as pressure sensitive adhesive (PSA). The coil  48  may optionally be attached to bottom housing  64  within a cutout area  68  sized and shaped to receive coil  48 . 
     In some situations, a user may place device  24  on a charging surface of device  12  so that rear surface  74  of the bottom housing  64  lies flat on the charging surface. In this exemplary configuration, a central axis of coil  48  extends parallel to a central axis of coil  42  in device  12  and a magnetic field from coil  42  may pass through coil  48 . The magnetic field induces current on coil  48  that is used to wirelessly charge device  24 . 
       FIG.  3 A  is a perspective view and  FIG.  3 B  is a top-down view of wireless power transmitting device  12  in an illustrative configuration. As shown, wireless power transmitting device  12  may have a coil  42  at charging surface  82  for transferring wireless power to coil  48  in power receiving device  24 . With one illustrative configuration, device  12  is a wireless charging puck having a planar surface  84  that opposes charging surface  82  and that rests on an underlying surface such as a tabletop or other surface. A user may place device  24  onto charging surface  82  for charging device  24 . Rear surface  74  of device  24  ( FIG.  2   ) and charging surface  82  lie within planes that are substantially parallel to the X-Y plane of  FIG.  3    during wireless charging. 
     Device  12  may drive coil  42  using a corresponding inverter  60  of  FIG.  1    to produce a magnetic field. The magnetic field passes through coil  48  while device  24  is placed on charging surface  82  and induces current on coil  48  that serves to wirelessly charge device  24 . Electromagnetic coupling between coil  42  and coil  48  is optimized when coil  48  is centered about coil  42 . However, the size of coil  42  allows for some positional tolerance along the X and Y axes of  FIG.  3    for the placement of device  24  on charging surface  82 . As noted above, the wireless charging efficiency of device  24  is determined, in part, by the coupling between coil  42  on device  12  and coil  48  on device  24 . 
       FIG.  4    is an illustrative plot of design constraints for prior art control method  400 .  FIG.  4    plots voltage on the Y axis and power on the X axis.  FIG.  4    includes an exemplary rectifier output voltage (“Vrect”) load line  410 A which occurs with a good coupling between the power transmitting device  12  and power receiving device  24 , and an exemplary Vrect load line  410 B which occurs with a bad coupling between the power transmitting device  12  and power receiving device  24 , both when the power transmitting device  12  inverter input voltage is at the maximum level. In the control method, the power receiving device attempts to regulate the rectifier output voltage at a constant target level  430 . The regulation is achievable in the region that the load line  410 A and  410 B are above the regulation target  430 , because the control loop can reduce the inverter input voltage to bring Vrect to the target level. The regulation is not achievable in the region where the load line  410 B is below the target level  430 , because the inverter input voltage cannot be increased further. With a good coupling, the system can achieve full power at  440 A. However, with a bad coupling, the system can only achieve a reduced power at  440 B, because the system is constrained by the maximum available inverter input voltage  420  and weak magnetic coupling between the wireless power transmitting and receiving devices. 
       FIG.  5    is an illustrative plot of a feedback control scheme for a wireless power transfer system according to an aspect of the present disclosure. A control loop implemented in the power receiving device  24  regulates the rectifier output voltage at a target level and allows the target rectifier output voltage to fold back (i.e., the target rectifier output voltage level is allowed to drop) when the power transmitting device inverter input voltage is at a maximum inverter input voltage level and the load increases. 
       FIG.  5    plots voltage on the Y axis and power on the X axis.  FIG.  5    includes an exemplary rectifier output voltage (“Vrect”) load line  510  which occurs with a bad coupling between the power transmitting device  12  and power receiving device  24 , when the power transmitting device inverter input voltage is at its maxim level. The load illustrated in load line  510  transitions from a light load to a heavy load as you move along the X axis from left to right. 
     Curve  520  plots the power transmitting device inverter input voltage. Curve  520  includes a first portion  520 A wherein, as the load represented in load line  510  increases, the inverter input voltage ramps up to a maximum inverter input voltage at  522 . As discussed below, the control loop is able to regulate the rectifier output voltage at a target level (i.e., Vrect regulation is achievable by the power receiving device) in this region of the inverter input voltage curve  520 . Curve  520  includes a second portion  520 B wherein the Vrect regulation is not achievable because the inverter input voltage is at the maximum level and cannot be further increased. Further increasing load power will cause Vrect to drop below the target level  530 . 
     Curve  530  plots the power receiving device rectifier target output voltage. As shown, curve  530  includes a first portion  530 A wherein the power receiving device regulates the rectifier output voltage at a target rectifier output voltage level as the load increases along load line  510 . Curve  530  includes a second portion  530 B wherein the power receiving device is operating in a target rectifier output voltage fold back mode that is triggered at  532  when the power transmitting device inverter input voltage is at a maximum level and the load continues to increase. The target rectifier output voltage fold back mode allows the target rectifier output voltage level to drop, and a control loop adaptively adjusts the target rectifier output voltage to a new target rectifier output voltage level as the load further increases along line  510 . While in the target rectifier output voltage fold back mode, the power receiving device control circuitry  30  may require the target rectifier output voltage to not drop below a predetermined minimum fold back rectifier output voltage level, thereby ensuring the rectifier  50  produces at least a minimum rectifier output power. 
     The target rectifier output voltage fold back mode control loop algorithm is implemented in the power receiving device  24 . During the wireless power transfer, the power transmitting device  12  may communicate information indicative of the inverter input voltage status to the power receiving device  24 . For example, the information may be a message that indicates the inverter input voltage is at a maximum inverter input voltage level. Alternatively, the information may identify the inverter input voltage value. The communication may be in a packet that carries the inverter input voltage information. In another example, the information may be a one-bit flag in an existing data packet to indicate whether the inverter input voltage has reached a maximum level. The communication from the power transmitter  12  to the power receiver  24  may take place using frequency shift keying (FSK) technique as discussed above. Alternatively, other types of in-band or out-of-band communications may be used, if desired. 
     In another example, the power receiving device  24  may ask the power transmitting device  12  for information indicative of an operating condition of an inverter of the power transmitting device, wherein the wireless power transfer coil  48  is receiving wireless power signals transmitted by the wireless power transmitting device  12  using the inverter. In addition, the information may comprise a status indicative of whether the inverter of the wireless power transfer device  12  is operating at its maximum input voltage. If the power transmitting device  12  responds to the power receiving device  24  indicating that the inverter input voltage is at a maximum level, the power receiving device  24  may trigger the target rectifier output voltage fold back mode as discussed above to adaptively adjust the target rectifier output voltage while the inverter input voltage is at the maximum level. 
       FIG.  6    is an illustrative plot of another feedback control scheme  600  for a wireless power transfer system according to an aspect of the present disclosure. Control scheme  600  may improve charging efficiency at a light load and includes the target rectifier output voltage fold back mode discussed above. Light load charging efficiency may be improved by reducing the power transmitting device inverter input voltage for a light load. A control loop implemented in the power receiving device  24  dynamically controls the target rectifier output voltage as a function of either the power receiving device rectifier output power or output current. As discussed below, the target rectifier output voltage level is low at a light load and increases to a high target rectifier output voltage level as the load increases to a heavy load. The load and target rectifier output voltage may depend on the power receiving device  24  operating conditions. Exemplary operating conditions include the battery&#39;s state of charge, whether the device is playing a video or running a power-hungry application such as a videogame. The target rectifier output voltage function (curve  630 ) may be designed for the best coupling condition and allow for the target rectifier output voltage to fold back in worse coupling conditions, as shown in the target rectifier output voltage function curve portion  630 C. 
       FIG.  6    plots voltage on the Y axis and power on the X axis.  FIG.  6    includes an exemplary rectifier output voltage (“Vrect”) load line  610  which occurs with a bad coupling between the power transmitting device  12  and power receiving device  24 , when the power transmitting device inverter input voltage is at its maxim level. The load illustrated in load line  610  transitions from a light load to a heavy load as you move along the X axis from left to right. 
     Curve  620  plots the power transmitting device inverter input voltage. Curve  620  includes a first portion  620 A wherein the transmitting device inverter input voltage is at a low level for a light load, as shown in the leftmost portion of load line  610 . Curve  620  includes a second portion  620 B wherein the inverter input voltage increases from the low level to a maximum inverter input voltage level at  622 , as the load represented in load line  610  transitions from a light load to a heavy load. Curve  620  includes a third portion  620 C that represents an operating condition where the inverter input voltage is at the maximum inverter input voltage level. 
     Curve  630  plots the power receiving device rectifier target output voltage as a function of rectifier output power. As shown, curve  630  includes a first portion  630 A wherein the rectifier output power is low and the rectifier output voltage is designed to be regulated at a minimum target rectifier output voltage level for a light load, as shown in the leftmost portion of load line  610 . Regulating the rectifier output voltage at the minimum target rectifier output voltage level may improve charging efficiency at light load because the inverter input voltage is maintained at a low voltage level (i.e., inverter input voltage curve first portion  620 A). 
     Curve  630  includes a second portion  630 B and a third portion  630 B′ wherein the rectifier output power is increasing, and the target rectifier output voltage is designed to increase from the minimum target rectifier output voltage level to a maximum target rectifier output voltage level  634  as the load transitions from a light load to a heavy load. However, due to a bad coupling between the power transmitter  12  and power receiver  24 , the power receiver may not be able to regulate the rectifier output voltage at the target rectifier output voltage level illustrated in the third portion  630 B 1  because the power transmitter inverter input voltage is at the maximum inverter input voltage level. In such case, the fourth portion  630 C of curve  630  illustrates the power receiving device operating in a target rectifier output voltage fold back mode that is triggered at  632  when the power transmitting device inverter input voltage is at a maximum level and the load along line  610  continues to increase. The target rectifier output voltage fold back mode allows the target rectifier output voltage level to drop, and a control loop adaptively adjusts the target rectifier output voltage to a new target rectifier output voltage level as the load further increases along line  610 . While in the target rectifier output voltage fold back mode, the power receiving device control circuitry  30  may require the target rectifier output voltage to not drop below a predetermined minimum fold back rectifier output voltage level, thereby ensuring the rectifier  50  produces at least a minimum rectifier output power. 
     The target rectifier output voltage fold back mode control loop algorithm is implemented in the power receiving device  24 . During the wireless power transfer, the power transmitting device  12  may communicate information indicative of the inverter input voltage status to the power receiving device  24 . For example, the information may be a message that indicates the inverter input voltage is at a maximum inverter input voltage level. Alternatively, the information may identify the inverter input voltage value. The communication may be in a packet that carries the inverter input voltage information. In another example, the information may be a one-bit flag in an existing data packet to indicate whether the inverter input voltage has reached a maximum level. The communication from the power transmitter  12  to the power receiver  24  may take place using frequency shift keying (FSK) technique as discussed above. Alternatively, other types of in-band or out-of-band communications may be used, if desired. 
     In another example, the power receiving device  24  may ask the power transmitting device  12  for information indicative of an operating condition of an inverter of the power transmitting device, wherein the wireless power transfer coil  48  is receiving wireless power signals transmitted by the wireless power transmitting device  12  using the inverter. In addition, the information may comprise a status indicative of whether the inverter of the wireless power transfer device  12  is operating at its maximum input voltage. If the power transmitting device  12  responds to the power receiving device  24  indicating that the inverter input voltage is at a maximum level, the power receiving device  24  may trigger the target rectifier output voltage fold back mode, as discussed above, to adaptively adjust the target rectifier output voltage while the inverter input voltage is at the maximum level. 
       FIG.  7    is a flow diagram of an exemplary control loop algorithm implemented in the power receiving device  24  of a wireless power transfer system using feedback control schemes  500  and  600  illustrated in  FIGS.  5  and  6   . The  FIG.  7    flow diagram will first be discussed in connection with an exemplary operation of feedback control scheme  500  shown in  FIG.  5   . 
     In a wireless power system  8 , a wireless power receiving device  24  is the master of communication and controls the power transfer in wireless power system  8 . Receiving device  24  is configured to receive electromagnetic signals  44  from a wireless power transmitting device  12 . Before and during power transfer, the receiving device  24  and transmitting device  12  may negotiate a maximum allowed power level. The power receiving device  24  includes a wireless power transfer coil  48 . In addition, receiving device  24  includes rectifier circuitry  50  that is coupled to the wireless power transfer coil  48  and configured to rectify signals from a wireless power transfer coil into output voltage. Receiving device  24  also includes control circuitry  30  that is configured to regulate the rectifier output voltage a target output voltage level (e.g.,  530 A in  FIG.  5   ), receive, from the transmitting device  12 , a status message indicative of the inverter input voltage, and adjust the target rectifier output voltage based on the status of the inverter input voltage. 
     Referring to  FIG.  7   , step  704 , receiving device  24  control circuitry  30  measures a present rectifier output voltage value (e.g., using circuitry  43 ) and determines if it is greater than or equal to the target voltage rectifier output level. If so, at step  706 , the receiving device may ramp up the load power until reaching the maximum allowed power and proceeds to step  708 . If the present rectifier output voltage value is less than the target rectifier output voltage level, the receiving device proceeds directly to step  708 . 
     At step  708 , receiving device  24  control circuitry  30  determines whether the inverter input voltage is at a maximum level, such as, an operating condition along inverter input voltage curve portion  520 B in  FIG.  5   . For example, control circuitry  30  may make this determination based on a status message indicative of an inverter input voltage received from the transmitting device  12 . In another example, the power receiving device  24  may ask the power transmitting device  12  for information indicative of the inverter input voltage status. In either example, if the status indicates the inverter input voltage is not at a maximum level (e.g., an operating condition along inverter input voltage curve first portion  520 A in  FIG.  5   ), receiving device  24  proceeds to step  710 . 
     At step  710 , control circuitry  30  regulates the rectifier output voltage at the target rectifier output voltage level. At step  712 , control circuitry  30  calculates a Control Error Packet (CEP) to enable the power transmitting device to adjust the rectifier output voltage by providing feedback information for the power transmitting device. At step  730 , receiving device  24  transmits the CEP to the transmitting device  12 . The transmitting device  12  may use information in the CEP to adjust the inverter input voltage. 
     Referring to step  708 , if receiving device  24  control circuitry  30  determines that the inverter input voltage status message indicates the inverter input voltage is at a maximum level (e.g., an operating condition along inverter input voltage curve second portion  520 B in  FIG.  5   ), the receiving device enters the target rectifier output voltage fold back mode (e.g., an operating condition along rectifier output voltage curve second portion  530 B). At step  720 , receiving device  24  control circuitry  30  measures a present rectifier output voltage value (e.g., using circuitry  43 ). While in the fold back mode, the present rectifier output voltage value may be below the target rectifier output voltage level. Therefore, receiving device  24  sets a new target rectifier output voltage level to the present rectifier output voltage value and regulates the rectifier output voltage at the new target rectifier output voltage level. At step  722 , the receiving device  24  does not calculate a Control Error Packet (CEP); rather, the receiving device  24  assigns the CEP a value that asks the power transmitting device  12  for more power. The CEP request for more power may cause the transmitting device  12  increase the inverter input voltage, thereby ensuring that the inverter input voltage is kept at the inverter input voltage maximum level. At step  730 , receiving device  24  transmits the CEP to the transmitting device  12 . 
     While the inverter input voltage is at a maximum level, receiving device  24  will continue to operate in the target rectifier output voltage fold back mode (i.e., steps  720  and  722  in  FIG.  7   ) and allow the rectifier output voltage to drop. The fold back mode enables the receiving device  24  to adaptively adjust the target rectifier output voltage level to a new target rectifier output voltage level as the load changes (e.g., an operating condition along rectifier output voltage curve second portion  530 B). While in the fold back mode, receiving device  24  control circuitry  30  may require the target rectifier output voltage level to not drop below a minimum fold back voltage level. Receiving device  24  control circuitry  30  may compare the present rectifier output voltage value measured at step  720  with the minimum fold back voltage level. If control circuitry  30  determines the present rectifier output voltage value is less than the minimum fold back voltage level, control circuitry  30  may set the new target rectifier output voltage level to the minimum fold back voltage level, and regulate the rectifier output voltage at the new target rectifier output voltage level. By controlling the minimum rectifier output voltage level, receiving device  24  may ensure that rectifier  50  produces a minimum output power. 
     Receiving device  24  will stop operating in the fold back mode when, at step  704 , the receiving device  24  control circuitry  30  determines the present rectifier output voltage value is greater than or equal to the target rectifier output voltage level (e.g., an operating condition along rectifier output voltage curve second portion  530 A in  FIG.  5   ). As such, the transmitting device  12  inverter input voltage will not be at a maximum level; rather, it will be in an operating condition along inverter input voltage curve first portion  520 A in  FIG.  5   . At step  708 , receiving device  24  will proceed to the control loop on left side of the  FIG.  7    flow diagram to regulate the rectifier output voltage at the target output voltage level and calculate a CEP in accordance with steps  710  and  712 . 
     The  FIG.  7    flow diagram will next be discussed in connection with an exemplary operation of feedback control scheme  600  shown in  FIG.  6   . As noted above, feedback control scheme  600  may improve charging efficiency at a light load and includes the target rectifier output voltage fold back mode control loop. 
     In a wireless power system  8 , a wireless power receiving device  24  is the master of communication and controls the power transfer in wireless power system  8 . Receiving device  24  is configured to receive electromagnetic signals  44  from a wireless power transmitting device  12 . Before and during power transfer, the receiving device  24  and transmitting device  12  may negotiate a maximum allowed power level. The power receiving device  24  includes a wireless power transfer coil  48 . In addition, receiving device  24  includes rectifier circuitry  50  that is coupled to the wireless power transfer coil  48  and configured to rectify signals from the wireless power transfer coil into output voltage. Receiving device  24  also includes control circuitry  30  that is configured to measure a characteristic of the rectifier circuitry  50  (e.g., using circuitry  43 ). For example, the rectifier circuitry characteristic may be the rectifier output power and/or the rectifier output current. 
     Control circuitry  30  may determine and dynamically control a target rectifier output voltage level based on a function of the measured characteristic of the rectifier circuitry  50 . For example, the target rectifier output voltage may be determined and controlled as a function of rectifier output power as shown in  FIG.  6    curve  630 . The target rectifier output voltage function (curve  630 ) may be designed for the best coupling condition (i.e., curve portions  630 A,  630 B,  630 B′) and allow for the target rectifier output voltage to fold back in worse coupling conditions (i.e., curve portion  630 C). The target rectifier output voltage function may provide a low target rectifier output voltage at light load (e.g., low rectifier output power required) and a high target rectifier output voltage at a heavy load (e.g., high rectifier output power required). 
     Referring to  FIG.  7    Step  704 , receiving device  24  control circuitry  30  measures a present rectifier output power (e.g., using circuitry  43 ) and determines a target rectifier output voltage level as a function of the measured rectifier output power. Control circuitry  30  also measures a present rectifier output voltage value and determines if it is greater than or equal to the target voltage rectifier output level. If so, at step  706 , the receiving device  24  may ramp up the load power until reaching the maximum allowed power and proceeds to step  708 . If the present rectifier output voltage value is less than the target rectifier output voltage level, the receiving device proceeds directly to step  708 . 
     At step  708 , receiving device  24  control circuitry  30  determines whether the inverter input voltage is at a maximum level, such as an operating condition along inverter input voltage curve portion  620 C in  FIG.  6   . For example, control circuitry  30  may make this determination based on a status message indicative of the inverter input voltage received from the transmitting device  12 . In another example, the power receiving device  24  may ask the power transmitting device  12  for information indicative of the inverter input voltage status. In either example, if the status indicates the inverter input voltage is not at a maximum level, such as an operating condition along inverter input voltage curve portions  620 A or  620 B in  FIG.  6   , the receiving device  24  proceeds to step  710 . 
     At step  710 , control circuitry  30  regulates the rectifier output voltage at the target output voltage level determined as a function of the measured rectifier output power (e.g., an operating condition along design target rectifier output voltage portion  630 A or  630 B in  FIG.  6   ). At step  712 , control circuitry  30  calculates a Control Error Packet (CEP) to enable the power receiving device to adjust the rectifier output voltage by providing feedback information for the power transmitting device. At step  730 , receiving device  24  transmits the CEP to the transmitting device  12 . The transmitting device  12  may use information in the CEP to adjust the inverter input voltage. 
     Referring, again, to step  708 , if receiving device  24  control circuitry  30  determines that the inverter input voltage status message indicates the inverter input voltage is at a maximum level (e.g., an operating condition along inverter input voltage curve portion  620 C in  FIG.  6   ), the receiving device enters the target rectifier output voltage fold back mode (e.g., an operating condition along rectifier output voltage curve portion  630 C). At step  720 , receiving device  24  control circuitry  30  measures a present rectifier output voltage value (e.g., using circuitry  43 ). While in the fold back mode, the present rectifier output voltage value may be below the target rectifier output voltage level. Therefore, receiving device  24  sets a new target rectifier output voltage level to the present rectifier output voltage value and regulates the rectifier output voltage at the new target rectifier output voltage level. At step  722 , the receiving device  24  does not calculate a CEP; rather, the receiving device  24  assigns the CEP a value that asks the power transmitting device  12  for more power. The CEP request for more power may cause the transmitting device  12  increase the inverter input voltage, thereby ensuring that the inverter input voltage is kept at the inverter input voltage maximum level. At step  730 , receiving device  24  transmits the CEP to the transmitting device  12 . 
     While the inverter input voltage is at a maximum level, receiving device  24  will continue to operate in the target rectifier output voltage fold back mode (i.e., steps  720  and  722  in  FIG.  7   ) and allow the rectifier output voltage to drop. The fold back mode enables the receiving device  24  to adaptively adjust the target rectifier output voltage level to a new target rectifier output voltage level as the load changes (e.g., an operating condition along rectifier output voltage curve portion  630 C). While in the fold back mode, receiving device  24  control circuitry  30  may require the target rectifier output voltage level to not drop below a minimum fold back voltage level. Receiving device  24  control circuitry  30  may compare the present rectifier output voltage value measured at step  720  with the minimum fold back voltage level. If control circuitry  30  determines the present rectifier output voltage value is less than the minimum fold back voltage level, control circuitry  30  may set the new target rectifier output voltage level to the minimum fold back voltage level, and regulate the rectifier output voltage at the new target rectifier output voltage level. By controlling the minimum rectifier output voltage level, receiving device  24  may ensure that rectifier  50  produces a minimum rectifier output power. 
     The foregoing description is provided for the purpose of explanation and is not to be construed as limiting the invention. While the invention has been described with reference to illustrative examples or methods, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Furthermore, although the invention has been described herein with reference to particular structure, methods, and examples, the invention is not intended to be limited to the particulars disclosed herein, as the invention extends to all structures, methods and uses that are within the scope of the appended claims. Those skilled in the relevant art, having the benefit of the teachings of this specification, may effect numerous modifications to the invention as described herein, and changes may be made without departing from the scope and spirit of the invention as defined by the appended claims.

Metadata:
Filing Date: 20220607
Publication Date: 20241015
Grant Date: 20241015
Priority Date: 20210618
Inventors: HU, ZHIYUAN
GHERGHESCU, ALIN I.
MEHRABI, Arash
BERDNIKOV, DMITRY
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00712", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L2001/125", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L1/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R19/165", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M1/0003", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00712", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 84283464