PATENT DOCUMENT

Publication Number: US-10978921-B1
Application Number: US-202016994308-A
Country: US
Kind Code: B1

Title: Wireless power system with efficiency prediction

Abstract:
A wireless power system has a wireless power transmitting device and a wireless power receiving device. During digital ping operations while the transmitting device and receiving device negotiate to establish a power level to use during normal operation, low-power wireless power signals may be transmitted to the receiving device from the wireless power transmitting device. Information gathered during the digital ping may be evaluated using a wireless-power-transmission-efficiency-to-digital-ping-rectifier-output-voltage relationship and using a normal-operation-wireless-power-transmission-efficiency-to-digital-ping-wireless-power-transmission-efficiency relationship to predict a wireless power transmission efficiency that would be experienced if the system were to enter normal operation. Based on this efficiency prediction, the system can issue alerts and can decide whether or not to enter normal operation.

Claims:
What is claimed is: 
     
       1. A wireless power transmitting device, comprising:
 wireless power transmitting circuitry configured to transmit wireless power signals to wireless power receiving circuitry that has a rectifier in a wireless power receiving device; and 
 control circuitry coupled to the wireless power transmitting circuitry, the control circuitry configured to:
 during digital ping operations in which the wireless power signals are transmitted from the wireless power transmitting circuitry to the wireless power receiving circuitry at a first wireless power level, obtain information on operation of the wireless power transmitting circuitry and the wireless power receiving circuitry, wherein the information includes a first wireless power transfer efficiency associated with transmitting the wireless power signals from the wireless power transmitting circuitry to the wireless power receiving circuitry at the first wireless power level; and 
 based on the first wireless power transfer efficiency, predict a second wireless power transfer efficiency associated with transmitting the wireless power signals at a second wireless power level after the digital ping operations have been completed. 
 
 
     
     
       2. The wireless power transmitting device of  claim 1  wherein the information comprises a first rectifier output voltage for the rectifier of the wireless power receiving circuitry and wherein the control circuitry is configured to predict the second wireless power transfer efficiency based on the first rectifier output voltage. 
     
     
       3. The wireless power transmitting device of  claim 2  wherein the control circuitry is configured to use a predetermined efficiency-voltage relationship between digital ping wireless power transfer efficiency and digital ping rectifier output voltage in predicting the second wireless power transfer efficiency. 
     
     
       4. The wireless power transmitting device of  claim 3  wherein the control circuitry is configured to use the first rectifier output voltage as an input to the predetermined efficiency-voltage relationship. 
     
     
       5. The wireless power transmitting device of  claim 4  wherein the control circuitry is configured to use the first wireless power transfer efficiency as an input to the predetermined efficiency-voltage relationship. 
     
     
       6. The wireless power transmitting device of  claim 5  wherein the control circuitry is configured to use an efficiency-efficiency relationship to predict the second wireless power transfer efficiency. 
     
     
       7. The wireless power transmitting device of  claim 6  wherein the control circuitry is configured to use, as an input to the efficiency-efficiency relationship, an efficiency value obtained from the efficiency-voltage relationship that corresponds to operation of the rectifier at a predetermined rectifier output voltage that is lower than the digital ping rectifier output voltage. 
     
     
       8. The wireless power transmitting device of  claim 7  wherein the control circuitry is configured to compare the second wireless power transfer efficiency to a predetermined threshold. 
     
     
       9. The wireless power transmitting device of  claim 8  wherein the control circuitry is configured to:
 in response to determining that the second wireless power transfer efficiency is greater than the predetermined threshold, control the wireless power transmitting circuitry to transmit the wireless power signals at the second wireless power level. 
 
     
     
       10. The wireless power transmitting device of  claim 8  wherein the control circuitry is configured to:
 in response to determining that the second wireless power transfer efficiency is greater than the predetermined threshold, direct the wireless power receiving device to issue an alert, wherein the alert indicates that a battery of the wireless power receiving device is charging. 
 
     
     
       11. The wireless power transmitting device of  claim 8  wherein the control circuitry is configured to:
 in response to determining that the second wireless power transfer efficiency is lower than the predetermined threshold, forgo controlling the wireless power transmitting circuitry to transmit the wireless power signals at the second wireless power level. 
 
     
     
       12. The wireless power transmitting device of  claim 8  wherein the control circuitry is configured to:
 in response to determining that the second wireless power transfer efficiency is lower than the predetermined threshold, direct the wireless power receiving device to issue an alert, wherein the alert indicates that wireless power transmission is not in progress. 
 
     
     
       13. The wireless power transmitting device of  claim 1  further comprising a plug configured to mate with an AC-to-DC power adapter, wherein the AC-to-DC power adapter has a power rating, wherein the control circuitry is configured to:
 obtain the power rating from the AC-to-DC power adapter when the plug is connected to the AC-to-DC power adapter, and 
 issue an alert based on the second wireless power transfer efficiency and the power rating. 
 
     
     
       14. A non-transitory computer-readable storage medium storing one or more programs configured to be executed by one or more processors of a wireless power transmitting device that, when executed, cause a wireless power transmitting device to provide wireless power charging operations to a wireless power receiving device, the computer-executable instructions comprising instructions for:
 during set-up operations, performing negotiations between the wireless power transmitting device and the wireless power receiving device to set up normal wireless power transmission operations that charge a battery in the wireless power receiving device; 
 during the set-up operations, determining a predicted efficiency value for wireless power transmissions from the wireless power transmitting device to the wireless power receiving device during the normal wireless power transmission operations; and 
 in response to determining that the predicted efficiency value is greater than a predetermined efficiency threshold, commencing the normal wireless power transmission operations. 
 
     
     
       15. The non-transitory computer-readable storage medium of  claim 14 , wherein the computer-executable instructions further comprise instructions for:
 using an efficiency-voltage relationship and an efficiency-efficiency relationship in determining the predicted efficiency value. 
 
     
     
       16. The non-transitory computer-readable storage medium of  claim 15 , wherein the computer-executable instructions further comprise instructions for:
 determining a first rectifier output voltage corresponding to operation of a rectifier in the wireless power receiving device during the set-up operations. 
 
     
     
       17. The non-transitory computer-readable storage medium of  claim 16 , wherein the computer-executable instructions further comprise instructions for:
 determining a first wireless power transmission efficiency value corresponding to wireless power transmission from the wireless power transmitting device to the wireless power receiving device during the set-up operations. 
 
     
     
       18. The non-transitory computer-readable storage medium of  claim 17 , wherein the efficiency-voltage relationship is a relationship between output voltage of the rectifier and efficiency of the wireless power transmission during the set-up operations and wherein the computer-executable instructions further comprise instructions for:
 determining an efficiency value from the efficiency-voltage relationship using as inputs: the first rectifier output voltage, the first wireless power transmission efficiency value, and a second rectifier output voltage that corresponds to operation of the rectifier during the normal wireless power transmission operations. 
 
     
     
       19. The non-transitory computer-readable storage medium of  claim 18 , wherein the efficiency-efficiency relationship is a relationship between set-up operation efficiency during the set-up operations and normal operation efficiency during the normal wireless power transmission operations and wherein the computer-executable instructions further comprise instructions for:
 determining the predicted efficiency value using the efficiency value determined from the efficiency-voltage relationship as an input to the efficiency-efficiency relationship. 
 
     
     
       20. The non-transitory computer-readable storage medium of  claim 14 , wherein the computer-executable instructions further comprise instructions for:
 in response to determining that the predicted efficiency value is greater than a predetermined efficiency threshold, causing the wireless power receiving device to present an alert indicating that the normal wireless power transmission operations are commencing. 
 
     
     
       21. The non-transitory computer-readable storage medium of  claim 14 , wherein the computer-executable instructions further comprise instructions for:
 in response to determining that the predicted efficiency value is greater than a predetermined efficiency threshold and before commencing the normal wireless power transmission operations, causing the wireless power receiving device to present a visual alert on a display of the wireless power receiving device indicating that the normal wireless power transmission operations are commencing. 
 
     
     
       22. A non-transitory computer-readable storage medium storing one or more programs configured to be executed by one or more processors of a wireless power transmitting device that, when executed, cause a wireless power transmitting device to provide wireless power charging operations to a wireless power receiving device, the computer-executable instructions comprising instructions for:
 during digital ping operations in which the wireless power transmitting device and the wireless power receiving device negotiate to establish a wireless power transmission level for normal wireless power transmission operations to charge a battery in the wireless power receiving device, predicting, using a wireless-power-transmission-efficiency-to-digital-ping-rectifier-output-voltage relationship and using a normal-operation-wireless-power-transmission-efficiency-to-digital-ping-wireless-power-transmission-efficiency relationship, an efficiency value for the normal wireless power transmission operations; and 
 in response to determining that the predicted efficiency value is greater than a predetermined efficiency threshold, commencing the normal wireless power transmission operations.

Description:
This application claims the benefit of provisional patent application No. 62/994,444, filed Mar. 25, 2020, 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 or charging puck wirelessly transmits power to a wireless power receiving device such as battery-powered or other portable electronic device. The portable electronic device has a coil and rectifier circuitry. The coil of the portable electronic device 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 has a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device may be a wireless charging mat, charging puck, or other device that transmits wireless power signals. The wireless power receiving device may be a portable electronic device that receives the transmitted wireless power signals from the wireless power transmitting device. 
     Before commencing normal wireless power transmission operations, the transmitting and receiving devices may perform set-up operations (sometimes referred to as handshake operations or digital ping operations). During these set-up operations, low-power wireless power signals may be transmitted from the wireless power transmitting device. Information on the operating state of the system such as rectifier output voltage, inverter input voltage, wireless power transfer efficiency, etc. may be gathered during the digital ping. This digital ping information may be processed using a wireless-power-transmission-efficiency-to-digital-ping-rectifier-output-voltage relationship and using a normal-operation-wireless-power-transmission-efficiency-to-digital-ping-wireless-power-transmission-efficiency relationship to predict a wireless power transmission efficiency that would be experienced if the system were to enter normal operation. 
     Based on the predicted normal operating efficiency value, the system can issue alerts and can decide whether or not to enter normal operation. 
    
    
     
       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 an illustrative wireless power system in accordance with an embodiment. 
         FIG. 3  is a graph of an illustrative efficiency-voltage relationship between rectifier output voltage and wireless power transfer efficiency during digital ping operations at a digital ping rectifier current in accordance with an embodiment. 
         FIG. 4  is a graph of an illustrative efficiency-efficiency relationship between wireless power transfer efficiency during digital ping operations and wireless power transfer efficiency during normal operation in accordance with an embodiment. 
         FIG. 5  is a flow chart of illustrative operations involved in operating a wireless power system in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system includes a wireless power transmitting device such as a wireless charging mat. The wireless power transmitting device wirelessly transmits power to one or more wireless power receiving devices. The wireless power receiving devices may include devices such as a wrist watches, cellular telephones, tablet computers, laptop computers, or other electronic equipment. Each wireless power receiving device uses power from the wireless power transmitting device for powering the device and for charging an internal battery. 
     Wireless power is transmitted from the wireless power transmitting device to a wireless power receiving device using one or more wireless power transmitting coils. The wireless power receiving device has one or more wireless power receiving coils coupled to rectifier circuitry. The rectifier circuitry converts received wireless power signals from the wireless power receiving coils into direct-current power. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , wireless power system  8  includes a wireless power transmitting device such as wireless power transmitting device  12  and includes a wireless power receiving device such as wireless power receiving device  24 . 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  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 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  and  24 , sending and receiving in-band and out-of-band data, making measurements, using in-band and/or out-of-band communications circuitry to transfer measurements, commands, alerts, and/or other information between devices  12  and  24 , 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  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 mat or charging puck that includes power adapter circuitry), may be a wireless charging mat or puck that is coupled 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 are sometimes described herein as an example. 
     Power receiving device  24  may be a portable electronic device such as a wrist watch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, or other electronic equipment. Power transmitting device  12  may be 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 embodiments, device  12  may obtain power from a stand-alone AC-DC power adapter such as AC-DC power converter  14 . Stand-alone power converter  14 ′ may have an AC plug that is plugged into a wall outlet. Converter  14 ′ may also have a connector such as connector  17 . Connector  17  may be a Universal Serial Bus (USB) connector or other connector configured to supply DC power. Device  12  may have an associated cable such as cable  13 . Cable  13  may have a connector that plugs into a corresponding connector in the body of device  12  or may be pigtailed to device  12 . During operation, cable  13  conveys DC power from converter  14 ′ to device  12 . Cable  13  may be a USB cable with a plug such as plug  15  (e.g., a USB plug) that is removably plugged into connector  17 . In arrangements such as these in which converter  14 ′ is a stand-alone AC-DC power adapter, device  12  may have a puck-shaped housing and may sometimes be referred to as forming a puck. Other housing shapes may be used for device  12 , if desired. 
     DC power from an internal power adapter or from a stand-alone power adapter such as converter  14 ′ that is conveyed to device  12  via a DC cable 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 . 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 coils  36 . These coil drive signals cause coil(s)  36  to transmit wireless power. Coils  36  may be arranged in a planar coil array (e.g., in configurations in which device  12  is a wireless charging mat) or may be arranged to form a cluster of coils (e.g., in configurations in which device  12  is a wireless charging puck). In some arrangements, device  12  (e.g., a charging mat, puck, portable device, 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 . 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 . 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 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 for creating visual output, a speaker for presenting output as audio signals, light-emitting diode status indicator lights and other light-emitting components for emitting light that provides a user with status information and/or other information, haptic devices for generating vibrations and other haptic output, and/or other output devices. Input-output devices  56  may also include sensors for gathering input from a user and/or for making measurements of the surroundings of system  8 . Illustrative sensors that may be included in input-output devices  56  include three-dimensional sensors (e.g., three-dimensional image sensors such as structured light sensors that emit beams of light and that use two-dimensional digital image sensors to gather image data for three-dimensional images from light spots that are produced when a target is illuminated by the beams of light, binocular three-dimensional image sensors that gather three-dimensional images using two or more cameras in a binocular imaging arrangement, three-dimensional lidar (light detection and ranging) sensors, three-dimensional radio-frequency sensors, or other sensors that gather three-dimensional image data), cameras (e.g., infrared and/or visible cameras with respective infrared and/or visible digital image sensors and/or ultraviolet light cameras), gaze tracking sensors (e.g., a gaze tracking system based on an image sensor and, if desired, a light source that emits one or more beams of light that are tracked using the image sensor after reflecting from a user&#39;s eyes), touch sensors, buttons, capacitive proximity sensors, light-based (optical) proximity sensors, other proximity sensors, force sensors, sensors such as contact sensors based on switches, gas sensors, pressure sensors, moisture sensors, magnetic sensors, audio sensors (microphones), ambient light sensors, optical sensors for making spectral measurements and other measurements on target objects (e.g., by emitting light and measuring reflected light), microphones for gathering voice commands and other audio input, distance sensors, sensors that are configured to gather information on motion, position, and/or orientation (e.g., accelerometers, gyroscopes, compasses, and/or inertial measurement units that include all of these sensors or a subset of one or two of these sensors), sensors such as buttons that detect button press input, joysticks with sensors that detect joystick movement, keyboards, and/or other sensors. Device  12  may 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 ) or input-output devices  70  may be omitted (e.g., to reduce device complexity). 
     Device  12  and/or device  24  may communicate wirelessly using in-band or out-of-band communications. Device  12  may, for example, have wireless transceiver circuitry  40  that wirelessly transmits out-of-band signals 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-band transmissions between devices  12  and  24  may be performed using coils  36  and  48 . 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. 
     It is desirable for power transmitting device  12  and power receiving device  24  to be able to communicate information such as received power, states of charge, and so forth, to control wireless power transfer. However, the above-described technology need not involve the transmission of personally identifiable information in order to function. Out of an abundance of caution, it is noted that to the extent that any implementation of this charging technology involves the use of personally identifiable information, implementers should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     Control circuitry  16  has measurement circuitry  41 . Measurement circuitry  41  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 housing of device  12  may have polymer walls, walls of other dielectric, metal structures, fabric, and/or other housing wall structures that enclose coils  36  and other circuitry of device  10 . The charging surface may be a planer outer surface of the upper housing wall of device  12 . 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 ). During object detection and characterization operations, external object measurement circuitry  41  can be used to make measurements on coils  36  to determine whether any devices  24  are present on device  12 . 
     In an illustrative arrangement, measurement circuitry  41  of control circuitry  16  contains signal generator circuitry (e.g., oscillator circuitry for generating AC probe signals at one or more probe frequencies and/or a pulse generator that can create impulses so that impulse responses can be measured to gather inductance information from the frequency of ringing signals created in response to the impulses and to gather Q-factor information from the decay envelope of the ringing signals, etc.) and signal detection circuitry (e.g., filters, analog-to-digital converters, impulse response measurement circuits, etc.). In some configurations. Q-factor measurements, inductance measurement, and other measurements may be made (e.g., before wireless power transmission operations have commenced, during wireless power transmission, during pauses between power transmission periods, and/or at other suitable times). Switching circuitry in device  12  may be used to switch desired coils into use during measurements on coils  36 , during wireless power transmission, etc. 
     Measurement circuitry  43  in control circuitry  30  may include signal generator circuitry, pulse generator circuitry, signal detection circuitry, and other and/or measurement circuitry (e.g., circuitry of the type described in connection with circuitry  41  in control circuitry  16 ). Circuitry  41  and/or circuitry  43  may be used in making current and voltage measurements (e.g., inverter input current and input voltage, rectifier output current and output voltage, etc.), measurements of transmitted and received power for power transmission efficiency estimates, coil Q-factor measurements, coil inductance measurements, coupling coefficient measurements, and/or other measurements. Based on this information or other information, control circuitry  30  can characterize the operation of devices  12  and  24 . For example, measurement circuitry  41  can measure coil(s)  36  to determine the inductance(s) and Q-factor value(s) for coil(s)  36 , can measure transmitted power in device  12  (e.g., by measuring the direct-current voltage powering inverter  61  and direct-current current of inverter  61  and/or by otherwise measuring voltages and currents in the wireless power transmitting circuitry of device  12 ), and can make other measurements on operating parameters associated with wireless power circuitry and other components in device  12 . In device  24 , measurement circuitry  43  can measure coil(s)  48  to determine the inductance(s) and Q-factor value(s) for those coil(s), can measure received power in device  24  (e.g., by measuring the output current and output voltage Vrect of rectifier  50  and/or by otherwise measuring voltages and currents in the wireless power receiving circuitry of device  24 ), and can make other measurements on the operating parameters associated with wireless power circuitry and other components in device  24 . 
     During negotiations between device  24  and  12  to set up normal power transmission (e.g., during initial wireless power transfer set-up operations before wireless power is ramped up to a level useful for battery charging) and/or later during wireless power transmission operations, measurements such as these may be used to configure system  8  (e.g., wireless power transmitting and receiving circuitry) to enhance wireless power transfer settings. Measurements such as these may also be used to help determine whether power is being lost due to the presence of a foreign object (e.g., a paper clip, coin, or other metallic object between or near devices  12  and  24 ) or whether devices  12  and  24  are otherwise not optimally aligned and ready for wireless power transfer. For example, the amount of power being received can be compared to the amount of power being transmitted to determine if losses are present that are associated with induced eddy currents in a foreign object. 
     This approach of comparing transmitted power and received power levels, which may sometimes be referred to as foreign object detection by power counting or power counting foreign object detection, can be used during normal wireless power transmission. In the event that a foreign object is detected during normal wireless power transmission operations, suitable action can be taken. For example, the amount of wireless power that is being transmitted can be lowered, wireless power transmission can be halted, an alert can be issued for a user, and/or other action may be taken. 
     Foreign object detection operations and operations determining whether the coils of devices  12  and  24  are misaligned can also be performed before normal wireless power transmission operations have commenced. For example, measurements with circuitry  41  and/or  43  (e.g., measurements of currents, voltages, inductances, Q-factors, wireless power transfer efficiencies, and other operating parameters) may be made during preliminary interactions between devices  12  and  24  (e.g., when a user initially places device  24  in proximity of device  12  for charging such as when a user initially places device  24  on a charging surface of device  12 ). 
     During these preliminary interactions, which may sometimes be referred to as digital ping operations, set-up operations, or transmitter-receiver preliminary negotiations, device  12  provides a relatively small amount of power (e.g., 200 mW or other small amount) to device  24  to awaken control circuitry in device  24  (e.g., without powering other load circuitry in device  24  such as display circuitry, battery charging circuitry, etc.). By powering the control circuitry and its associated communications circuitry in device  24 , devices  12  and  24  can negotiate over a wireless link (e.g., an in-band link) to determine whether to proceed with normal wireless power transfer operations and to determine an appropriate wireless power transfer level for system  8  to use during normal 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 digital ping power transmission power). 
     To inform a user that wireless power transmission operations (e.g., operations associated with charging battery  58 ) are proceeding properly (e.g., to inform the user that this process has not been terminated due to presence of a foreign object), the user may be provided with an alert. The alert, which may sometimes be referred to as a chime, may include audio and/or visual output presented on device  24  (as an example). For example, a chime may involve presentation of an audible chime tone and a visual user interface affordance (e.g., a battery charging icon or other visual alert displayed on a display in device  24  or other display). By providing the chime, the user is reassured that charging operations are proceeding normally (e.g., so that the user is comfortable walking away from system  8  and leaving devices  12  and  24  unattended until charging is complete). 
     Digital ping operations are typically performed relatively quickly (e.g., over a time period of 200 ms or less, less than 50 ms, less than 1 s, or other relatively short time period). Subsequent negotiations between device  12  and device  24  leading to commencement of normal (high power) power transmission operations can take significantly longer (e.g., several seconds or more). If the presentation of the chime is delayed significantly (e.g., for more than a second or so), the user may become concerned that wireless power transfer operations are not proceeding normally. If, on the other hand, the chime is presented before system  8  has determined that no foreign objects are present, there is a risk that a foreign object that is present will only be detected later (e.g., during normal operation using a power counting foreign object detection technique, at which point the user may have departed and not be present to observe that charging operations have failed). 
     To ensure that the chime is provided sufficiently early, the chime may, if desired, be presented during digital ping operations. This provides the user with prompt assurance (e.g., within a second or less) that wireless power will be transmitted normally and that the battery device  24  will be satisfactorily charged (e.g., after many minutes or hours). To prevent undesired false chimes (which are later invalid because a foreign object is detected only during power counting operations during normal wireless power transmission), foreign object detection operations (and operations detecting coil misalignment) are performed early as well. In particular, foreign object detection operations and/or wireless transmission efficiency evaluations for detecting misalignment may be performed during digital ping operations. In response to determining that devices  12  and  24  are satisfactorily aligned and that no foreign object is present during these digital ping foreign object detection operations, the chime may be presented to the user (e.g., with a speaker, display, and/or other output devices in device  24 ). 
     With an illustrative embodiment, foreign objects or other conditions that make it unsuitable to begin normal wireless power transmission operations (e.g., coil misalignment conditions) can be detected during digital ping operations by using information gathered during the digital ping to predict the wireless power transfer efficiency that will be achieved during subsequent normal operation. The predicted efficiency value may, as an example, be compared to a predetermined threshold amount. If the predicted efficiency is sufficiently high, system  8  can conclude that the coils of system  8  are aligned satisfactorily and that no foreign objects are present. System  8  may therefore enter normal operation, the chime may be presented to the user (e.g., device  12  may direct device  24  to issue an alert indicating that a battery of device  24  is charging), and wireless power may be transmitted at normal operation power levels from device  12  to device  24 . If, however, the predicted efficiently is low, system  8  may forgo transmitting wireless power at elevated levels. System  8  may, if desired, alert the user that efficiency is low (e.g., because devices  12  and  24  may not be aligned properly) and/or may return to performing efficiency monitoring operations and other digital ping operations (e.g., device  12  may direct device  24  to issue an alert indicating that wireless power transmission is not in progress). 
       FIG. 2  is a circuit diagram of illustrative circuitry that may be used in system  8 . As shown in  FIG. 2 , wireless power transmitting circuitry  52  may receive direct current power at wireless power transmitting circuitry input terminals  80  and may use inverter circuitry  61  (e.g., transistor-based switches) to produce and drive AC currents through coil  36  to transmit wireless power signals  44  (e.g., magnetic flux) from coil  36 . Wireless power receiving circuitry  54  uses coil  48  to receive the wirelessly transmitted signals  44  and uses rectifier circuitry  50  (e.g., transistor-based switches and capacitor C) to convert the received signals to DC power (output voltage Vrect) at output terminals  82  or rectifier  50  (which are the output terminals of wireless power receiving circuitry  54 ). In the example of  FIG. 2 , the switches of circuitry  54  have a full-bridge configuration, which allows circuitry  54  to operate also as an inverter in wireless power transmitting circuitry (e.g., in a mode in which device  24  is transmitting power to an external device such as device  12 ). The switches of circuitry  52  of  FIG. 2  also have a full-bridge configuration, which allows circuitry  52  to be operated as a rectifier in wireless power receiving circuitry to receive wireless power transmitted by device  24  to device  12 . If desired, circuitry  52  may be configured to only operate as a wireless power transmitter and circuitry  54  may be configured to only operate as a wireless power receiver. 
     In the circuit of  FIG. 2 , measurement circuitry  41  may be used to monitor the operation of circuitry  52 . For example, measurement circuitry  41  may be used to monitor the DC current flowing to circuitry  52  from the power supply of device  12  (e.g., the input current to inverter  61  and circuitry  52 ) and may be used to monitor the input voltage to inverter  61  and circuitry  52 . In this way, the power supplied to circuitry  52  may be measured. Measurement circuitry  43  may be used to monitor the output voltage Vrect of rectifier  50  in circuitry  54  and may be used to measure the corresponding output current of rectifier  50  and circuitry  54 . The measured values of rectifier output voltage and rectifier output current may be used to determine the output power of receiving circuitry  54 . The measurements of circuitry  43  can be conveyed to device  12  during digital ping operations and/or at other times (e.g., using in-band communications) and/or the measurements of circuitry  41  can be conveyed to device  24  during digital ping operations and/or at other times (e.g., using in-band communications). By sharing these measurements, control circuitry in system  8  (e.g., device  12  and/or device  24 ) can measure wireless power transfer efficiency levels and can share this information. In some examples, the efficiency of device  12  in transferring wireless power to device  24  can be measured by control circuitry  16  ( FIG. 1 ) by dividing the received power (power supplied at the output of circuitry  54 ) by the transmitted power (power supplied at the input of circuitry  52 ). In some examples, the efficiency of device  12  in transferring wireless power to device  24  can be measured by control circuitry  30  ( FIG. 1 ) by dividing the received power (power supplied at the output of circuitry  54 ) by the transmitted power (power supplied at the input of circuitry  52 ). 
     The operation of system  8  tends to be non-linear, which can present challenges in trying to predict the wireless power transfer efficiency that will be achieved during normal operation (sometimes referred to herein as ηno) from measurements made when not operating at normal power levels. For example, it can be challenging to use measurements from circuits  41  and  43  that are obtained during digital ping operations (where power levels may be, for example, about 200 mW) to predict ηno. This can make it challenging to use digital ping measurements to determine whether or not to proceed to normal operation. User experience may be impacted if digital ping measurements lead to wireless power transfer operations that charge a battery too slowly. 
     In accordance with an embodiment, the operation of system  8  may be characterized in advance to determine relationships between digital ping measurements and subsequent operation at normal power levels. Using these relationships, digital ping measurements can be used to accurately predict the efficiency levels that will likely be achieved during subsequent wireless power transfer operations at higher power. If the predicted efficiency during normal operation is insufficient, system  8  can conclude that a foreign object is present between devices  12  and  24  that is preventing satisfactorily wireless power transfer and/or can conclude that devices  12  and  24  (e.g., coils  36  and  48 ) are misaligned or that other non-optimal conditions are present. System  8  (e.g., device  12 ) can then forgo wireless power transfer operations at the elevated powers associated with normal operation, and can optionally alert the user of system  8  and/or take other suitable action. If predicted normal operation efficiency is sufficiently high, system  8  may increase the amount of wireless power that is being transmitted and can proceed with normal operation, and can optionally alert the user that normal operation is commencing. 
     The operation of system  8  can be characterized using mathematical models and/or using empirical techniques. Factors that influence wireless power transmission efficiency include power transmission levels, rectifier output voltage Vrect, rectifier output current Irect, magnetic coupling between devices  12  and  24 , etc. To characterize system  8  under a variety of potential operating conditions, robotic measurement equipment and/or other equipment for monitoring the performance of system  8  may make system measurements while varying the relative position of coils  36  and  48  (e.g., by moving device  24  to a variety of different positions relative to device  12  such as different vertical separations Z and different lateral positions X and Y). These measurements may include measurements made at different operating currents Irect. For example, a series of measurements may be made at a first rectifier output current (e.g., a first current level such as a current of 25 mA or other relatively low current that is associated with digital ping operations) and a series of measurements may be made at a second rectifier output current (e.g. a second current level such as a current of 75 mA or other relatively high current that is associated with higher power operations such as normal wireless power transfer operations during the normal powering of device  24  to perform tasks such as charging battery  58 , operating input-output devices  56  such as a display, etc.). At each of the different relative coil positions and at each of the operating currents, measurements may be made over a range of output voltages Vrect. Efficiency measurements may also be made at different power levels during these measurements. 
     The characterizing measurements, which may be made, for example, during manufacturing, may be used to produce a family of curves such as the family of curves of  FIG. 3  and may be used to produce a curve such as the curve of  FIG. 4 . The curves of  FIG. 3  represent a wireless-power-transmission-efficiency-to-digital-ping-rectifier-voltage relationship. The curve of  FIG. 4  represents a normal-operation-wireless-power-transmission-efficiency-to-digital-ping-wireless-power-transmission-efficiency relationship. These relationships may be used to help accurately predict the efficiency that system  8  will exhibit during wireless power transmission at normal power conditions from digital ping measurements involving wireless power transmission at reduced power conditions. 
     During digital ping operations, the output current from circuitry  54  may be maintained at the first current level (e.g., 25 mA). For example, measurement circuitry  43  may measure the output current from circuitry  54  and can inform device  12  whenever the output current starts to rise above 25 mA (e.g., to direct device  12  to decrease the amount of wireless power being transmitted) and whenever the output current starts to fall below 25 mA (e.g., to direct device  12  to increase the amount of wireless power being transmitted). Using this type of feedback arrangement or other closed-loop control scheme, the amount of wireless power being transmitted from device  12  to device  24  can be regulated to ensure that Irect stays constant at the 25 mA (or other suitable first current value). 
     While maintaining Irect at 25 mA, the value of Vrect across terminals  82  is allowed to fluctuate. In a typical scenario, the value of Vrect might rise above the normal operating voltage output level from circuitry  54 . During normal operation, for example. Vrect may be 6 V (as an example), whereas during digital ping operations in which Irect is held at 25 mA, Vrect may be larger than 6 V. As an example, Vrect may be 10 V during digital ping operations at a 25 mA rectifier output current. The value of voltage Vrect during digital ping operations (e.g., 10 V in this example) may sometime be referred to as the digital ping rectifier output voltage. 
     The power transfer efficiency of system  8  varies as a function of Irect and Vrect. During digital ping operations, Irect is maintained at the first current level (e.g., 25 mA), while the value of Vrect floats and is measured by measurement circuitry  43 . A relatively small amount of power (e.g., 250 mW) is drawn by the circuitry of device  24  during digital ping. The measured value of the output of circuitry  54  during digital ping is Vrectmeas. In an illustrative scenario, when Irect is maintained at 25 mA during digital ping operations, Vrect can become 10 V (Vrectmeas=10 V). A digital ping efficiency ηdpmeas is associated with operation of device  24  at Irect=25 mA and Vrect=Vrectmeas (e.g., 10 V). The value of ηdpmeas is equal to the output power Pout from circuitry  54  divided by input power Pin to circuitry  52  while Irect is at the digital ping current level of 25 mA and Vrect=Vrectmeas. In the illustrative scenario of  FIG. 3 , when Irect=25 mA and Vrectmeas is 10V, the value of ηdpmeas is 12%. 
     The family of curves of  FIG. 3  represents a relationship between digital ping wireless power transfer efficiency ηdp (output power Pout from circuitry  54  divided by input power Pin into circuitry  52  while Irect is at the digital ping current level of 25 mA) and voltage Vrect. Five representative curves in this family of curves are shown in  FIG. 3 . By making multiple measurements over a variety of relative positions between devices  12  and  24 , numerous curves (e.g., tens, hundreds, or thousands of curves for this family) can be measured. 
     Using the relationship of  FIG. 3 , the value of wireless power transfer efficiency that would be obtained during digital ping if Vrect were at its normal operating value can be obtained from the measured value Vrectmeas and the measured value of digital ping efficiency ηdpmeas at Vrectmeas. Consider, as an example, a scenario in which the normal operating voltage at the output of circuitry  54  is 6V (e.g., Vrect=6 V during normal operation). During these normal operations, while wireless power is being transmitted from device  12  to device  24 , the output power and output current of circuitry  54  are at normal levels (e.g., the output power is above the digital ping power level and the Irect value is above the digital ping value). To determine the digital ping efficiency of system  8  at the normal operating voltage of 6V, the value of Vrectmeas and the measured digital ping wireless power transfer efficiency ηdpmeas=12% may be used to select a matching curve from the family of curves of  FIG. 3 . The identified curve (curve  90  in this example) can then be used to determine what the value of ηdp would be at a normal Vrect operating voltage of 6V. This predicted ηdp value, which is labeled as ηdp6V in  FIG. 3 , may be 17% (as an example). 
     To compactly represent the overall relationship embodied by the family of curves of  FIG. 3 , so that this information can be stored efficiently in system  8  (e.g., in control circuitry  16  of device  12  and/or other storage in device  12  and/or device  24 ), a curve-fitting process may be performed. In an illustrative embodiment, polynomial curve fitting may be used. For example, all of the curves in the family of curves can be averaged to produce an average curve. Using quadratic curve fitting, the values of A and B may then be obtained for equation 1.
 
η dp=A [( V rect) 2 −( V rectmeas) 2 ]+ B [ V rect− V rectmeas]+ηmeas  (1)
 
     In equation 1, ηdp is digital ping wireless power transfer efficiency, Vrect is the output voltage of rectifier  50 . Vrectmeas is the value of Vrect when Irect is maintained at the digital ping current (e.g., at 25 mA), and ηmeas is the measured efficiency offset at Vrect=Vrectmeas. From the quadratic curve fitting, values for A and B may be obtained such as A=0.001 and B=−0.0027 (as an example). 
     After determining the value of ηdp6V from the digital ping efficiency versus rectifier output voltage relationship of equation 1 using the measured digital ping efficiency ηmeas and the measured digital ping rectifier output voltage Vrectmeas as inputs, the efficiency at normal operating voltage Vrect=6 V and a targeted Irect value (e.g., a predetermined Irect value or an Irect value obtained from device  24  during digital ping such as an Irect value of 75 mA or other value that may be associated with normal operation) may be obtained using the relationship of  FIG. 4 . The curve of  FIG. 4  represents a normal-operation-wireless-power-transmission-efficiency-to-digital-ping-wireless-power-transmission-efficiency relationship and can be used to predict normal operation efficiency ηno at 6 V from the digital ping efficiency at 6 V (ηdp6V) that is produced using the relationship of  FIG. 3 . The efficiency-efficiency relationship of  FIG. 4  may be obtained empirically (e.g., from efficiency measurements made while varying the relative positions between devices  24  and  12  as described in connection with the empirical measurements of  FIG. 3 ). As with the relationship of equation 1, any suitable storage techniques may be used to store this information in system  8  (e.g., look-up tables, equations, etc.) If desired, curve fitting (e.g., polynomial curve fitting such as quadratic curve fitting) may be used to produce the values of C, D, and ηos in equation 2 and this equation may be stored in system  8 .
 
η no=Cηdp   2   +Dηdp+ηos   (2)
 
     In the illustrative embodiment. C is −1.7112. D is 1.8348, and offset value ηos is 0.0053. 
     In the present example, ηdp6V is 17%, so the value of ηno from the relationship of  FIG. 4  is 27%. The relationship of  FIG. 4  therefore produces a desired final result—the predicted efficiency ηno that is expected to be obtained during normal operation at the normal Vrect operation voltage (6 V in this example). The value of ηno corresponds to operation at a different rectifier current than used during digital ping (e.g., 75 mA or other value that is higher than the 25 mA level of digital ping operations). The predicted normal operation efficiency value ηno can be compared to a predetermined threshold value and suitable action taken in response to the outcome of this comparison. 
     Illustrative operations involved in transferring wireless power in system  8  are shown in  FIG. 5 . 
     During the operations of block  100 , measurement circuitry  41  may perform measurements to determine whether device  24  is present on device  12  (e.g., to determine whether coil  48  is present on coil  36 ). These measurements may include, for example, measuring the impedance of coil  36 , measuring the Q factor of coil  36 , and/or performing other measurements that indicate when wireless power receiving device  24  has been brought into proximity of wireless power transmitting device  12 . These operations may be performed periodically until the presence of device  24  is detected. 
     In response to determining that device  24  is present, operations may proceed to block  102 . During the operations of block  102 , system  8  may perform set-up operations between devices  12  and  24  (sometimes referred to as a digital ping). The set-up operations involve transmitting a small amount of power wirelessly from device  12  to device  24  (e.g., 250 mW) and performing negotiations to establish normal wireless power transmission operations. During the digital ping, devices  12  and  24  may use measurement circuitry (e.g., measurement circuitry  41  in device  12  and measurement circuitry  43  in device  24 ) to measure operating voltages and currents. In-band communications or other wireless communications may be used to allow device  24  to transmit measurements and/or commands to device  12  so that device  12  can increase and decrease the amount of wireless power being transmitted in system  8 , thereby maintain the output current of circuitry  54  at a desired value (e.g., Irect=25 mA in the present example). Device  12  may use information on the input current and voltage of circuitry  52  and the output current and voltage of circuitry  54  to determine Vrectmeas and ηdpmeas. 
     After obtaining Vrectmeas and ηdpmeas, these values can be used as inputs to the relationship of  FIG. 3  (e.g., the relationship of equation 1). This allows system  8  (e.g., device  12 ) to determine the value of ηdp at a normal operating voltage associated with normal wireless power transmission (e.g., a Vrect voltage associated with normal operation of system  8  such as the Vrect value associated with normal operation of system  8  at a rectifier output power above the digital ping output power). In the present example, this Vrect value is 6 V, so ηdp is evaluated at 6 V, thereby producing ηdp6V. The Vrect value of 6 V during normal operation serves as an additional input to the relationship of  FIG. 3 . 
     During the operation of block  106 , the value of ηdp6V that was obtained from the output of the efficiency-voltage relationship of  FIG. 3  is used as an input to the efficiency-efficiency relationship of  FIG. 4  (e.g., the relationship of equation 2). This allows system  8  (e.g., device  12 ) to predict the operating efficiency ηno of system  8  during normal operation at the normal Vrect value (Vrect=6 V) and an Irect value of 75 mA or other suitable normal operating current that is larger than the digital ping rectifier current (25 mA in this example). 
     During the operations of block  106 , the value of ηno may be compared to a predetermined threshold efficiency value. The threshold TH may have a value of 20% or other suitable threshold value. 
     If the predicted normal operating efficiency for system  8  is less than TH, operations may continue during block  102  (e.g., additional digital ping operations may be performed). If desired, a warning message such as a visual and/or an audible warning (alert) may be presented to a user (e.g., using a display in device  24 , etc.). Device  12  may send a command to device  24  that directs device  24  to present the warning and/or device  12  may present a warning. 
     In response to determining that ηno is greater than TH, appropriate action may be taken during the operations of block  108 . As an example, wireless power transmission may commence so that wireless power signals  44  may be transmitted from device  12  to device  24  at normal operating powers (e.g., a power level greater than the digital ping power level). During normal operation, system  8  may continuously adjust the amount of wireless power being transmitted (e.g., device  12  may transmit more or less power based on commands from device  24 , and/or other control schemes may be used to adjust the amount of transferred wireless power). If desired, system  8  (e.g., device  24 ) may be used to present visual and/or audible messages to a user to indicate that normal wireless power transmission operations will commence or have commenced (e.g., an audible chime tone and a visual user interface affordance such as a battery charging icon or other visual alert may be presented by system  8 ). For example, in response to determining that ηno is greater than TH, a visible battery charging icon may be presented on the display of device  24  (e.g., in response to a command sent wirelessly from device  12  to device  24 ), an audible tone indicating that charging has been successfully started may be issued, and/or other alert information may be presented to a user. 
     Different power transmitting devices  12  may have different power transmission capabilities. For example, the power rating of a first power transmitting device may be 5 W, whereas the power rating of a second power transmitting device may be 10 W. In configurations in which device  12  is receiving DC power from a stand-alone power adapter, the power rating of the combined system (device  12  and the stand-alone power adapter) may be determined by the power rating of the power adapter. For example, device  12  may be a wireless charging puck that can be plugged into various different USB power adapters (see, e.g., AC-DC converter  14 ′ of  FIG. 1 , which may be housed within a stand-alone housing that is separate from the housing of device  12 ). When plugged into a USB power adapter with a first power rating, device  12  will at most be able to use a first amount of DC input power to transmit wireless power signals, whereas when plugged into a USB power adapter with a second power rating that is larger than the first power rating, device  12  will be able to use the larger second amount of DC input power in transmitting wireless power. 
     For a given wireless power transmission efficiency level, a self-contained power transmitting device with a higher power rating or a power transmitting device that has a higher power rating by virtue of being coupled to a higher-rated stand-alone AC-DC power adapter will be able to transmit more power to power receiving device  24  than a lower-rated stand-alone power transmitting device or a power transmitting device coupled to a stand-alone AC-DC power adapter with a lower power rating. 
     Variations between different types of transmitting device configurations may, if desired, be taken into account when determining whether or not to begin normal operation (e.g., when analyzing the predicted normal operation efficiency to determine whether to proceed to the normal operations of block  108  or to return instead to the digital ping operations of block  102 ). 
     Consider, as an example, a scenario in which a user has two power transmitting devices (e.g., one located at home and the other at work). The first of the devices may be powered by a stand-alone USB power adapter with a power rating of 10 W and the second of the devices may be powered by a stand-alone USB power adapter with a power rating of 5 W. It may be desirable to ensure that the user is provide with a relatively uniform user experience despite switching back and forth between these two different charging configurations from time to time. 
     To help ensure that the user&#39;s experience is satisfactorily uniform, in both situations chime should occur only if a minimum charging experience can be achieved. If use of the first and second power transmitting devices to charge power receiving device  24  results in the issuance of identical chimes but widely different charging times, the user may be unnecessarily confused. 
     User confusion can be reduced by causing chimes to be issued based both on the predicted charging efficiency and on the power transmitting capability of the transmitting device (sometimes referred to as the power rating of the device). The power transmitting capacity of each transmitting device may, in configurations with stand-alone AC-DC power adapters, be dictated by the power rating of the stand-alone AC-DC power adapter that is connected to each device  12  rather than an inherent power transmitting limit of that device  12 . As a result of issuing chimes based both on the predicted efficiency and power transmitting capability for each device  12 , a device with the ability to deliver a higher power may be given some leeway with respect to the required efficiency threshold level (threshold TH) for normal operation (or, put another way, a lower power rated system may be held to a higher standard than a higher power rated system). 
     For example, a somewhat stringent threshold (e.g., a first threshold TH 1  of 20%) may be imposed for lower power transmitting devices such as power transmitting devices  12  coupled to USB power adapters with power ratings of 5 W, whereas a more lenient threshold (e.g., a second threshold TH 2  of 10%) may be imposed for higher power transmitting devices such as power transmitting devices  12  coupled to USB power adapters with power ratings of 10 W. In effect, this type of approach bases the decision on whether to issue a chime to the user and proceed to normal operation at block  108  on a prediction of the amount of power to be transmitted during charging (equal to the efficiency multiplied by the power rating) and a comparison of this predicted power transfer level to a power transfer level threshold. 
     Each stand-alone power transmitting device  12  may store information on its power rating (e.g., 5 W, 10 W, etc.) in storage (e.g., in control circuitry  16  in that power transmitting device). Each power transmitting device  12  that is coupled to a USB power adapter or other stand-alone AC-DC power adapter (converter  14 ′ of  FIG. 1 ) with a power rating may obtain the power rating of the power adapter via USB data communications (e.g., communications using the USB-PD standard) or other communications with that power adapter. The power adapters themselves may have control circuitry such as control circuitry  16  of device  12  that contains memory in which the power rating of the power adapter is stored. Power rating information for device  12  and/or adapters  14  may, as an example, be programmed into memory in during manufacturing. When used in system  8 , device  12  can retrieve power rating information from an associated stand-alone power adapter (and can optionally store this information locally) by querying the power adapter over the USB cable between device  12  and the power adapter (as an example). Device  12  can the use this power rating information in assessing the power transmission capabilities of device  12  (e.g., the power rating of the adapter may effectively become the power rating of device  12 ) and can use the power rating information in determining when to issue chimes. 
     By basing the criteria used to determine whether to enter normal operation on both efficiency information and on transmitter power rating information, the user may be presented with chimes in a reasonably consistent fashion. A user would not, for example, be provided with a chime indicating that charging is proceeding properly only because the predicted normal operating efficiency exceeds a fixed threshold. Rather, the chime would only be provided if the efficiency and power rating taken together are deemed to be capable of providing a user with a reasonable charging time. 
     In general, any suitable technique may be used to implement a decision scheme based on both predicted normal operation wireless power transfer efficiency and power transmitting device transmitting power capacity. In one embodiment, the predicted normal operation efficiency is multiplied by the transmitting power capacity of device  12  to produce a predicted normal operation power transfer level, which may then be compared to a power level threshold that is uniform across transmitters with different power ratings. In another embodiment, the predicated normal operation efficiency is compared to an efficiency threshold that varies as a function of power transfer capacity. To ensure that lower-rated devices (e.g., devices  12  that are coupled to 5 W adapters) can charge properly, these lower-rated devices may be required to exhibit higher predicted normal operation efficiency values than higher-rated devices (e.g., devices  12  that are coupled to 10 W adapters). 
     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: 20200814
Publication Date: 20210413
Grant Date: 20210413
Priority Date: 20200325
Inventors: WANG, GE
TERRY, STEPHEN C.
MALAN, Wynand
HARRIS, ZACHARY S.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/0047", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "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": false, "tree": "[]"}, {"code": "H04B5/0037", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B5/79", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B5/79", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/79", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 75394257