PATENT DOCUMENT

Publication Number: US-10978899-B2
Application Number: US-201815884199-A
Country: US
Kind Code: B2

Title: Wireless charging system with duty cycle control

Abstract:
A wireless power transmitting device transmits wireless power signals to a wireless power receiving device by supplying drive signals with a duty cycle to a wireless power transmitting coil. The wireless power receiving device has a rectifier and a wireless power receiving coil that receives wireless power signals having the duty cycle from the wireless power transmitting device. The rectifier is coupled to an integrated circuit such as a battery charger integrated circuit. The amount of current drawn by the integrated circuit from the rectifier is adjustable. During operation, control circuitry in the wireless power receiving device sets the current to multiple different values while using sensor circuitry to measure output power from the rectifier. A satisfactory value for the duty cycle can be identified by adjusting the duty cycle while observing when peaks in the output power arise as a function of the different current values.

Claims:
What is claimed is: 
     
       1. A wireless power receiving device configured to receive power from a wireless power transmitting device that has an inverter configured to supply a drive signal with an associated duty cycle and that has at least one wireless power transmitting coil configured to receive the drive signal and to transmit corresponding wireless power signals to the wireless power receiving device, the wireless power receiving device comprising:
 a wireless power receiving coil configured to receive the wireless power signals; 
 rectifier circuitry coupled to the wireless power receiving coil that is configured to supply output power based on the received wireless power signals; 
 battery charger circuitry configured to receive the output power, wherein the battery charger circuitry is configured to receive a current from the rectifier circuitry; and 
 control circuitry configured to:
 adjust the current received by the battery charger circuitry to a set of current values to identify a corresponding output power value for each current value in the set of current values, the corresponding output power value being the output power supplied by the rectifier circuitry, 
 identify a peak in the output power based on the corresponding output power values exhibited by adjusting the current to the set of current values, and 
 in response to identifying the peak, determine whether a desired power is being supplied to the battery charger at the peak. 
 
 
     
     
       2. The wireless power receiving device defined in  claim 1  wherein the control circuitry is further configured to provide duty cycle change requests to the wireless power transmitting device that direct the wireless power transmitting device to adjust the duty cycle of the drive signal. 
     
     
       3. The wireless power receiving device defined in  claim 2  wherein the control circuitry is configured to provide the duty cycle change requests to the wireless power transmitting device at least partly in response to determining that the desired power is being supplied to the battery charger at the peak. 
     
     
       4. The wireless power receiving device defined in  claim 3  wherein the control circuitry is coupled to the wireless power receiving coil and wherein the control circuitry is configured to transmit the duty cycle change requests to the wireless power transmitting device using the wireless power receiving coil. 
     
     
       5. The wireless power receiving device defined in  claim 3  wherein the control circuitry is configured to wirelessly transmit the duty cycle change requests to the wireless power transmitting device. 
     
     
       6. The wireless power receiving device defined in  claim 2  wherein the control circuitry is configured to provide the duty cycle change requests to the wireless power transmitting device at least partly in response to determining that the desired power is not being supplied to the battery charger at the peak. 
     
     
       7. The wireless power receiving device defined in  claim 1  wherein adjusting the current comprises adjusting a maximum current drawn by the battery charger circuitry from the rectifier circuitry. 
     
     
       8. The wireless power receiving device defined in  claim 1  further comprising sensor circuitry that is coupled between the rectifier circuitry and the battery charger circuitry. 
     
     
       9. The wireless power receiving device defined in  claim 8  wherein the sensor circuitry comprises a current sensor that measures the current and a voltage sensor. 
     
     
       10. The wireless power receiving device defined in  claim 8  wherein the control circuitry is configured to measure the output power using the sensor circuitry. 
     
     
       11. The wireless power receiving device defined in  claim 1  further comprising:
 a display coupled to the control circuitry. 
 
     
     
       12. The wireless power receiving device defined in  claim 1  further comprising:
 a battery, wherein the battery charger circuitry is configured to charge the battery. 
 
     
     
       13. A wireless power receiving device configured to receive power from a wireless power transmitting device having a wireless power transmitting coil that is configured to receive drive signals having a duty cycle and produce corresponding wireless power signals with the duty cycle, the wireless power receiving device comprising:
 a wireless power receiving coil configured to receive the wireless power signals from the wireless power transmitting device; 
 rectifier circuitry coupled to the wireless power receiving coil that is configured to supply output power based on the received wireless power signals; 
 battery charger circuitry configured to receive the output power, wherein the battery charger circuitry is configured to receive a current from the rectifier circuitry using a path between the battery charger circuitry and the rectifier circuitry; 
 sensor circuitry coupled to the path between the rectifier circuitry and the battery charger circuitry; and 
 control circuitry configured to measure the output power at the path using the sensor circuitry to identify a peak in the output power while adjusting the current. 
 
     
     
       14. The wireless power receiving device defined in  claim 13  wherein the control circuitry is configured to adjust the duty cycle by wirelessly communicating with the wireless power transmitting device. 
     
     
       15. The wireless power receiving device defined in  claim 14  wherein the control circuitry is configured to identify the peak in the output power while adjusting the current while receiving the wireless power signals at the adjusted duty cycle. 
     
     
       16. The wireless power receiving device defined in  claim 15  wherein the control circuitry is configured to:
 wirelessly transmit a duty cycle change request to the wireless power transmitting device in response to identifying the peak in the output power while adjusting the current while receiving the wireless power signals at the adjusted duty cycle. 
 
     
     
       17. The wireless power receiving device defined in  claim 13  wherein the control circuitry is configured to determine whether a desired power is being supplied to the battery charging circuitry at the peak and, in response to determining that the desired power is not being supplied, transmitting a duty cycle change request to the wireless power transmitting equipment that directs the wireless power transmitting equipment to increase the duty cycle. 
     
     
       18. The wireless power receiving device defined in  claim 17  further comprising a battery, wherein the rectifier and the battery charger are configured to charge the battery while the rectifier receives the wireless power signals from the wireless power receiving coil at the increased duty cycle. 
     
     
       19. A wireless power receiving device configured to receive power from a wireless power transmitting device that has an inverter configured to supply a drive signal with an associated duty cycle and that has at least one wireless power transmitting coil configured to receive the drive signal and to transmit corresponding wireless power signals with the duty cycle to the wireless power receiving device, the wireless power receiving device comprising:
 a wireless power receiving coil configured to receive the transmitted wireless power signals with the duty cycle; 
 rectifier circuitry coupled to the wireless power receiving coil that is configured to supply output power based on the wireless power signals received with the wireless power receiving coil; 
 an integrated circuit configured to receive the output power from the rectifier circuitry while drawing a current from the rectifier circuitry; and 
 control circuitry configured to adjust the duty cycle of the drive signal based at least partly on measurements from sensor circuitry that identify a peak in the output power across multiple values of the current. 
 
     
     
       20. The wireless power receiving device defined in  claim 19  wherein the control circuitry is configured to wirelessly transmit duty cycle change requests to the wireless power transmitting device to adjust the duty cycle. 
     
     
       21. The wireless power receiving device defined in  claim 20  further comprising:
 a display; and 
 a battery configured to receive power from the integrated circuit. 
 
     
     
       22. The wireless power receiving device defined in  claim 21  wherein the integrated circuit comprises a battery charger integrated circuit and wherein the control circuit is configured to identify the peak in the output power across multiple values of the current by adjusting the battery charger integrated circuit to draw the multiple values of the current.

Description:
This application claims the benefit of provisional patent application No. 62/453,861, filed Feb. 2, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to wireless systems, and, more particularly, to systems in which devices are wirelessly charged. 
     BACKGROUND 
     In a wireless charging system, a wireless power transmitting device such as a device with a charging surface wirelessly transmits power to a portable electronic device. The portable electronic device receives the wirelessly transmitted power and uses this power to charge an internal battery and power components. It can be challenging to regulate the flow of wireless power in a wireless charging system. If care is not taken, wireless power transfer efficiency may not be optimized and power delivery requirements may not be satisfied. 
     SUMMARY 
     A wireless power transmitting device transmits wireless power signals to a wireless power receiving device by supplying drive signals with a duty cycle to a wireless power transmitting coil. During operation, the wireless power receiving device wirelessly controls the wireless power transmitting device to help enhance wireless power transfer efficiency. 
     The wireless power receiving device has a rectifier and a wireless power receiving coil. The wireless power receiving coil receives wireless power signals having the duty cycle from the wireless power transmitting device. The rectifier is coupled to a power circuit (e.g., an integrated circuit) such as a battery charger integrated circuit. The battery charger circuit is coupled to a battery to charge the battery. 
     The amount of current drawn by the battery charger circuit from the rectifier is adjustable. During operation, control circuitry in the wireless power receiving device sets the current to multiple different values while using sensor circuitry that is coupled between the rectifier and the battery charger circuit to measure output power from the rectifier. A satisfactory value for the duty cycle can be identified by adjusting the duty cycle while observing when peaks arise in the output power across the different current values. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless charging system in accordance with some embodiments. 
         FIG. 2  is a top view of an illustrative wireless power transmitting device with an array of coils that forms a wireless charging surface in accordance with an embodiment. 
         FIG. 3  is a circuit diagram of an illustrative wireless charging system in accordance with an embodiment. 
         FIG. 4  is a graph showing how the duty cycle of a wireless charging system drive signal and associated wireless power signal transmitted by a wireless power transmitting coil and received by a wireless power receiving coil may be varied during operation in accordance with an embodiment. 
         FIGS. 5 and 6  are graphs in which wireless power transfer efficiency has been plotted as a function of drive signal duty cycle in two different respective coupling coefficient scenarios in accordance with an embodiment. 
         FIG. 7  is a graph in which wireless power receiving circuit output power has been plotted as a function of battery charger current for different drive signal duty cycles in accordance with an embodiment. 
         FIGS. 8, 9, 10, and 11  show respectively how wireless power receiving circuit output power, wireless charging system drive signal duty cycle, wireless power transfer efficiency, and wireless power receiving circuit output voltage may vary as a function of time in an illustrative usage scenario in accordance with an embodiment. 
         FIG. 12  is a flow chart of illustrative operations that may be performed by a wireless power transmitting device in accordance with an embodiment. 
         FIG. 13  is a flow chart of illustrative operations that may be performed by a wireless power receiving device in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system has a wireless power transmitting device that transmits power wirelessly to a wireless power receiving device. The wireless power transmitting device is a device such as a wireless charging mat, wireless charging puck, wireless charging stand, wireless charging table, or other wireless power transmitting equipment. The wireless power transmitting device has one or more coils that are used in transmitting wireless power to one or more wireless power receiving coils in the wireless power receiving device. The wireless power receiving device is a device such as a cellular telephone, watch, media player, tablet computer, pair of earbuds, remote control, laptop computer, other portable electronic device, or other wireless power receiving equipment. 
     During operation, the wireless power transmitting device supplies alternating-current drive signals to one or more wireless power transmitting coils. This causes the coils to transmit alternating-current electromagnetic signals (sometimes referred to as wireless power signals) to one or more corresponding coils in the wireless power receiving device. Rectifier circuitry in the wireless power receiving device converts received wireless power signals into direct-current (DC) power for powering the wireless power receiving device. 
     The wireless power system uses a control scheme that helps enhance wireless power transfer efficiency while satisfying power demands from the wireless power receiving device. During operation, the wireless power receiving device makes changes to the current drawn by a battery charger circuit in the wireless power receiving device and makes duty cycle adjustments to the wireless power transmitting device drive signals and wireless power signals while monitoring output power from the rectifier circuitry with sensor circuitry. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , wireless power system  8  includes wireless power transmitting device  12  and one or more wireless power receiving devices such as wireless power receiving device  10 . Device  12  may be a stand-alone device such as a wireless charging mat, may be built into furniture, or may be other wireless charging equipment. Device  10  is a portable electronic device such as a wristwatch, a cellular telephone, a tablet computer, or other electronic equipment. Illustrative configurations in which device  12  is a mat or other equipment that forms a wireless charging surface and in which device  10  is a portable electronic device that rests on the wireless charging surface during wireless power transfer operations are sometimes be described herein as examples. 
     During operation of system  8 , a user places one or more devices  10  on the charging surface of device  12 . Power transmitting device  12  is coupled to a source of alternating-current voltage such as alternating-current power source  50  (e.g., a wall outlet that supplies line power or other source of mains electricity), has a battery such as battery  38  for supplying power, and/or is coupled to another source of power. A power converter such as alternating-current-to-direct current (AC-DC) power converter  40  can convert power from a mains power source or other alternating-current (AC) power source into direct-current (DC) power that is used to power control circuitry  42  and other circuitry in device  12 . During operation, control circuitry  42  uses wireless power transmitting circuitry  34  and one or more coil(s)  36  coupled to circuitry  34  to transmit alternating-current electromagnetic signals  48  to device  10  and thereby convey wireless power to wireless power receiving circuitry  46  of device  10 . 
     Power transmitting circuitry  34  has switching circuitry (e.g., transistors in an inverter circuit) that are turned on and off based on control signals provided by control circuitry  42  to create AC current signals (drive signals) through coil(s)  36 . As the AC currents pass through coil(s)  36 , alternating-current electromagnetic fields (wireless power signals  48 ) are produced that are received by corresponding coil(s)  14  coupled to wireless power receiving circuitry  46  in receiving device  10 . When the alternating-current electromagnetic fields are received by coil  14 , corresponding alternating-current currents and voltages are induced in coil  14 . Rectifier circuitry in circuitry  46  converts received AC signals (received alternating-current currents and voltages associated with wireless power signals) from coil(s)  14  into DC voltage signals for powering device  10 . The DC voltages are used in powering components in device  10  such as display  52 , touch sensor components and other sensors  54  (e.g., accelerometers, force sensors, temperature sensors, light sensors, pressure sensors, gas sensors, moisture sensors, magnetic sensors, etc.), wireless communications circuits  56  for communicating wirelessly with control circuitry  42  of device  12  and/or other equipment, audio components, and other components (e.g., input-output devices  22  and/or control circuitry  20 ) and are used in charging an internal battery in device  10  such as battery  18 . 
     Devices  12  and  10  include control circuitry  42  and  20 . Control circuitry  42  and  20  includes storage and processing circuitry such as microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. Control circuitry  42  and  20  is configured to execute instructions for implementing desired control and communications features in system  8 . For example, control circuitry  42  and/or  20  may be used in determining power transmission levels, processing sensor data, processing user input, processing other information such as information on wireless coupling efficiency from transmitting circuitry  34 , processing information from receiving circuitry  46 , using information from circuitry  34  and/or  46  such as signal measurements on output circuitry in circuitry  34  and other information from circuitry  34  and/or  46  to determine when to start and stop wireless charging operations, adjusting charging parameters such as charging frequencies, coil assignments in a multi-coil array, and wireless power transmission levels, and performing other control functions. Control circuitry  42  and  20  may be configured to support wireless communications between devices  12  and  10  (e.g., circuits  42  and/or  20  may include wireless communications circuitry such as circuitry  56 ). Control circuitry  42  and/or  20  may be configured to perform these operations using hardware (e.g., dedicated hardware or circuitry) and/or software (e.g., code that runs on the hardware of system  8 ). Software code for performing these operations is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media). The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, other computer readable media, or combinations of these computer readable media or other storage. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  42  and/or  20 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, or other processing circuitry. 
     Device  12  and/or device  10  may communicate wirelessly during operation of system  8 . Devices  10  and  12  may, for example, have wireless transceiver circuitry in control circuitry  42  and  20  (see, e.g., wireless communications circuitry such as circuitry  56  of  FIG. 1 ) that allows wireless transmission of signals between devices  10  and  12  (e.g., using antennas that are separate from coils  36  and  14  to transmit and receive unidirectional or bidirectional wireless signals, using coils  36  and  14  to transmit and receive unidirectional or bidirectional wireless signals, etc.). 
     With one illustrative configuration, wireless transmitting device  12  is a wireless charging mat or other wireless power transmitting equipment that has an array of coils  36  that supply wireless power over a wireless charging surface. This type of arrangement is shown in  FIG. 2 . In the example of  FIG. 2 , device  12  has an array of coils  36  that lie in the X-Y plane. Coils  36  of device  12  are covered by a planar dielectric structure such as a plastic member or other structure forming charging surface  60 . The lateral dimensions (X and Y dimensions) of the array of coils  36  in device  36  may be 1-1000 cm, 5-50 cm, more than 5 cm, more than 20 cm, less than 200 cm, less than 75 cm, or other suitable size. Coils  36  may overlap or may be arranged in a non-overlapping configuration. Coils  36  can be placed in a rectangular array having rows and columns and/or may be tiled using a hexagonal tile pattern or other pattern. 
     During operation, a user places one or more devices  10  on charging surface  60  in locations such as locations  62  and  64 . The position at which a device  10  is located on surface  60  affects alignment between the coil  14  in that device and coil(s)  36  in device  12 . Variations in alignment, in turn, affect magnetic coupling (coupling coefficient k) between the coils in devices  12  and  10 . In addition to variations in coupling coefficient k, the amount of power that is desired by device  10  at any given point in time may vary. For example, device  10  may wish to draw a relatively large amount of power to charge battery  18  when battery  18  is depleted and may wish to draw a relatively small amount of power when battery  18  is fully charged. Due to variations in operating conditions in system  8  such as changes in coupling coefficient k and desired power draw (desired rectifier output power) in device  10 , wireless charging system performance will vary. As an example, wireless power transfer efficiency will vary as operating conditions change. System  8  therefore makes real-time adjustments to system operating parameters such as the duty cycle of the alternating-current drive signal that drives current through coil(s)  36 . These adjustments may help enhance wireless power transfer efficiency while supplying a battery charger or other components in device  10  with desired amounts of power. 
     A circuit diagram of illustrative circuitry for wireless power transfer (wireless power charging) system  8  is shown in  FIG. 3 . As shown in  FIG. 3 , wireless power transmitting circuitry  34  includes an inverter such as inverter  70  or other drive circuit that produces alternating-current drive signals such as variable duty-cycle square waves. These signals are driven through an output circuit that includes coil(s)  36  and capacitor(s)  72  to produce wireless power signals with the same variable duty cycle that are transmitted wirelessly to device  10 . A single coil  36  is shown in the example of  FIG. 3 . In general, device  12  may have any suitable number of coils (1-100, more than 5, more than 10, fewer than 40, fewer than 30, 5-25, etc.). Switching circuitry (sometimes referred to as multiplexer circuitry) that is controlled by control circuitry  42  can be located before and/or after each coil  36  and/or before and/or after the other components of output circuit  71  and can be used to switch desired sets of one or more coils  36  (desired output circuits  71 ) into or out of use. For example, if it is determined that device  10  is located in location  62  of  FIG. 2 , the coil(s) overlapping device  10  at location  62  may be activated during wireless power transmission operations while other coils  36  (e.g., coils not overlapped by device  10  in this example) are turned off. 
     Control circuitry  42  and control circuitry  20  contain wireless transceiver circuits (e.g., circuits such as wireless communication circuitry  56  of  FIG. 1 ) for supporting wireless data transmission between devices  12  and  10 . In device  10 , control circuitry  20  can use path  90  and coil  14  to transmit data to device  12 . In device  12 , paths such as path  74  may be used to supply incoming data signals that have been received from device  10  using coil  36  to demodulating (receiver) circuitry in the communications circuitry of control circuitry  42 . If desired, path  74  may be used in transmitting wireless data to device  10  with coil  36  that is received by receiver circuitry in control circuitry  20  using coil  14  and path  90 . Configurations in which control circuitry  20  and control circuitry  42  have antennas that are separate from coils  36  and  14  may also be used for supporting unidirectional and/or bidirectional wireless communications between devices  12  and  10 , if desired. 
     During wireless power transmission operations, transistors in inverter  70  are controlled using AC control signals from control circuitry  42 . Control circuitry  42  can use control path  76  to supply control signals to the gates of the transistors in inverter  70 . The duty cycle of these control signals and therefore the duty cycle of the drive signals applied by inverter  70  to coil  36  and the resulting duty cycle of the corresponding wireless power signals produced by coil  36  can be adjusted dynamically. 
     Wireless power receiving device  10  has wireless power receiving circuitry  46 . Circuitry  46  includes rectifier circuitry  80  (e.g., a synchronous rectifier controlled by signals from control circuitry  20 ) that converts received alternating-current signals from coil  14  (e.g., wireless power signals received by coil  14 ) into direct-current (DC) power signals for battery charger circuitry  86  and other input-output devices  22 . A power circuit such as battery charger circuitry  86  (e.g., a battery charging integrated circuit or other power management integrated circuit or integrated circuits) receives power from rectifier circuitry  80  and regulates the flow of this power to battery  18 . Control circuitry  20  (e.g., control circuitry in a battery charging integrated circuit and/or separate control circuitry) adjusts operating parameters for charger circuitry  86 . For example, control circuitry  20  supplies control signals to battery charger circuitry  86  that adjust the current draw and therefore the power draw of battery charger circuitry  86  from rectifier circuitry  80  in real time. The amount of current Iout flowing on path  88  between rectifier circuitry  80  and battery charger circuitry  86  and the voltage Vout on path  88  can be measured by control circuitry  20  using sensor circuitry such as current sensor  82  and voltage sensor  84 . Control circuitry  20  measures output power Pout by determining the product of Iout and Vout. 
       FIG. 4  is a graph of illustrative alternating-current drive signals being applied by inverter  70  to coil  36 . The duty cycle of the drive signal is defined as the ratio of on time T 1  to total time T 2  in each period. The length of T 2  may correspond to an operating frequency for the drive signal of between 100 and 500 kHz, 360 kHz, less than 400 kHz, more than 200 kHz, or other suitable frequency. In the example of  FIG. 4 , signal  92  has a first duty cycle (e.g., 50%) and signal  94  has a second duty cycle (e.g., 25%). In general, control circuitry  42  can make adjustments to the control signals on path  76  so that any suitable duty cycle (e.g., a duty cycle of 0-50%) is produced by inverter  70  during wireless power transmission. 
     Due to factors such as the location of device  10  on surface  60  relative to coil(s)  36 , coupling coefficient k between coil(s)  36  and coil  14  varies between charging events. The Q factor of coils  36  and  14  may vary between devices. This can affect wireless power transfer efficiency between device  12  and device  10 . The graphs of  FIGS. 5 and 6  illustrate how variations in coupling coefficient k affect wireless power transfer efficiency (Eff) between devices  12  and  10 . The curves of  FIG. 5  corresponding to a higher coupling coefficient (stronger coupling) than the curves of  FIG. 6  (which correspond to a weak coupling scenario). In each graph, efficiency Eff has been plotted as a function of coil drive signal duty cycle (DC) for four different amounts of power (Pout) being delivered between circuitry  80  and circuitry  86  of  FIG. 3  (e.g., P 1 , P 2 , P 3 , and P 4 ). With one illustrative configuration, P 1  is 1 W, P 2 , is 2.5 W, P 3  is 5 W, and P 4  is 7.5 W. Each of the curves in  FIGS. 5 and 6  exhibits a general increase in power transfer efficiency with decreasing duty cycle until further efficiency increases are no longer possible (the left-hand ends of the curves). Further efficiency increases from further reductions in duty cycle are not possible because the desired amount of power (P 1 , P 2 , P 3 , or P 4  in this example) cannot be delivered to circuitry  86  and battery  18  under those operating conditions (e.g., the voltage Vout from circuit  80  and therefore Pout drops when too much current is drawn by circuit  86 ). The graphs of  FIGS. 5 and 6  demonstrate that maximum system efficiency depends on coupling coefficient k, load power demand (P 1 , P 2 , P 3 , P 4 , etc.), and duty cycle. For a fixed load power (Pout), efficiency generally increases as inverter duty cycle decreases, but system  8  will not be able to meet certain load power demands when duty cycle is too low. 
     To identify satisfactory operating conditions for system  8 , control circuitry  20  dynamically adjusts the requested current draw (sometimes referred to as Iref) for battery charger circuitry  86 , thereby adjusting the output current Iout of rectifier circuitry  80  and the amount of power (Pout=Vout*Iout) that is delivered to the load of device  10  (charger  86  and battery  18  in the example of  FIG. 3 ). The values of Pout that are produced across a range of various Iref values will depend of duty cycle, as shown in  FIG. 7 . 
     In the example of  FIG. 7 , Pout has been plotted as a function of current between circuit  80  and circuit  86  (Iref=Iout). Each of the curves in  FIG. 7  corresponds to a different duty cycle (e.g., 20%, 22%, 23%, 24%, or 28%). For lower duty cycles (e.g., 20% and 22% in this example), rectifier output power Pout increases as rectifier output current Iout (battery charger input current Iref) increases, then decreases after reaching a peak value. For higher duty cycles (e.g., 23%, 24%, or 28%), Pout increases as Iout and Iref increase then remain at the load power level. Pout may be used to power battery charger  86  (as shown in  FIG. 3 ) and/or other components (see, e.g., input-output devices  22  of  FIG. 1 ). In situations in which the duty cycle is sufficiently high to supply a desired level of Pout, Pout will not exhibit a peak. If the duty cycle is insufficient, Pout will peak across multiple current values. 
     Control circuitry  20  can exploit this behavior when searching for a satisfactory duty cycle for use in operating system  8  to supply a desired amount of power to the load of device  10  (charger circuitry  86 ). In particular, control circuitry  20  can measure Pout while sweeping the current Iout across multiple values at each of multiple different duty cycles. Control circuitry  20  can use these measurements to find the maximum duty cycle that exhibits a peak in Pout. The minimum duty cycle for use in supplying the desired amount of power to the load of device  10  can then be set to a duty cycle value that is just above the maximum duty cycle that exhibits the peak (e.g., one step above the maximum duty cycle, where the step size is 0.1%-1%, less than 0.2%, more than 0.05%, or other duty cycle step size). This control scheme allows system  8  to enhance system performance by lowering duty cycle whenever possible to increase efficiency while ensuring that a currently desired power can be delivered to circuit  86 . As the currently desired power for circuit  86  changes during operation (e.g., because battery  18  becomes fully charged), the search for the satisfactory operating duty cycle can be updated accordingly. Duty cycle fine tuning operations may also be performed (e.g., by making fine adjustments to the duty cycle that has been identified to help further optimize efficiency). 
       FIGS. 8, 9, 10, and 11  show how duty cycle ( FIG. 9 ) may be adjusted to enhance efficiency ( FIG. 10 ). In this example, the desired power for circuit  86  varies as a function of time. Control circuitry  20  can obtain information on the currently desired power for circuitry  86  from circuit  86  (as an example). Initially (time t=t 0 ), battery  18  is depleted. As a result, the amount of power that is desired by battery charger  86  is relatively high (5.6 W). This desire for high power is present between times t 0  and t 1  in  FIG. 8 . During this time period, control circuitry  20  lowers the inverter duty cycle from 42% to 25% as shown in  FIG. 9 , thereby increasing efficiency from 64% to 68% as shown in  FIG. 10 . At time t 1 , the duty cycle has been lowered so much that it is no longer possible to supply the desired output power. This is illustrated by the drop in output voltage Vout at time t 1  and the associated momentary drop in Pout from circuit  80 . Control circuitry  20  can use sensor circuitry such as sensors  82  and  84  to measure the current (Iout) and voltage (Vout) associated with the power signals being supplied from rectifier circuitry  80 . When it is determined that the duty cycle can no longer be lowered without adversely affecting the ability to supply a desired value of Pout to circuit  86 , further reductions in duty cycle can be halted. As shown in  FIG. 9 , for example, control circuitry  20  can maintain the duty cycle at a satisfactory constant level between times t 1  and t 2 . 
     At times greater than t 2 , the amount of power desired by battery charger circuit  86  continues to fluctuate and control circuitry  20  responds accordingly. Control circuitry  20  can decrease the duty cycle whenever possible to enhance efficiency and can increase the duty cycle whenever necessary to ensure that the currently desired power is satisfactorily supplied to circuitry  86 . 
       FIGS. 12 and 13  are flow charts of illustrative operations involved in controlling system  8 . Initially, a user places device  10  on surface  60  of device  12 . Device  12  may contain a foreign object detection system (e.g., a detection circuit coupled to coil  36  or a detection system using a separate set of coils) that detects when device  10  has been placed on surface  60 . In response to detection that device  10  is present in the vicinity of device  12 , device  12  and device  10  establish a wireless communications link (blocks  98  and  118  of  FIGS. 12 and 13 ). During subsequent operations, device  10  uses the communications link to send information to device  12  and device  12  uses the communications link to send information to device  10 . The information that is conveyed over the communications link includes control commands, sensor data, required power settings, operating parameters, and/or other information. 
     The communications link allows devices  10  and  12  to establish initial operating conditions. For example, the communications link allows device  12  to inform device  10  of the power delivery capabilities of device  12  (e.g., “current maximum available power is 5.6 W”). The communications link also allows device  10  to receive this information from device  12  and to acknowledge the received information. The link allows devices  10  and  12  to identify each other and confirm that control operations can be performed securely. 
     Device  10  can set initial operating parameters during the operations of block  118 . For example, battery charger circuitry  86  can use information on the current charge status of battery  18  or other information to establish a desired level of power to receive from circuitry  80  and to use in charging battery  18 . If battery  18  is depleted and should be rapidly charged, the desired operating power for circuitry  86  (sometimes referred to as load power or load demand) may be set to be equal to the maximum available wireless power from device  12 . If battery  18  is nearly full, the desired load power can be set to a lower level (e.g., 1.0 W). Battery charger circuitry  86  can monitor the state of battery  18  in real time and can update the current desired level of power for battery charger circuitry  86  accordingly. 
     After the wireless communications link has been established between devices  12  and  10  and desired authentication operations have been satisfactorily performed, wireless charging can begin. During charging, device  12  serves as a slave while device  10  serves as a master. As shown in  FIG. 12 , for example, after device  12  provides its current maximum available power level (P_in) to device  10  at block  100 , device  12  waits for signals from device  10  at block  102  and analyzes information from device  10  at block  104  to determine whether a duty cycle change request has been received from device  10 . In the absence of a duty cycle change request, control can loop back to block  100 , as shown by line  108 . In response to receiving a request from device  10  to change the inverter duty cycle, control circuitry  42  of device  12  adjusts the duty cycle of the control signals supplied to inverter  70  over control signal path  76 , thereby adjusting the duty cycle of the corresponding drive signals supplied by inverter  70  to output circuit  71  and the corresponding duty cycle of the wireless power signals transmitted from device  12  to device  10 . 
     The flow chart of  FIG. 13  illustrates the control scheme used by device  10  and system  8 . The flow chart of  FIG. 13  shows how device  10  implements three control loops: a peak power point loop, a load power loop, and a peak efficiency loop. 
     During the peak power point loop (blocks  122 ,  124 , and  126  and line  128 ), the current flowing between circuits  80  and  86  is adjusted (e.g., the current is swept across multiple values ranging from a low value to a high value) while control circuitry  20  uses sensing circuitry  82  and  84  to monitors output power (Pout) on path  88  (e.g., by measuring current Iout and output voltage Vout and by determining the product of Iout and Vout). This allows control circuitry  20  to identify whether a peak in output power Pout exists for the current duty cycle setting. 
     During the load power loop (block  130 , line  132 , and block  120 ) control circuitry  20  determines whether the currently desired power can be supplied at the current duty cycle setting. 
     During the peak efficiency loop (blocks  134 ,  138 ,  140 , and line  142 ), control circuitry  20  makes fine-tuning adjustments to the duty cycle to help increase efficiency. 
     At block  120 , device  10  uses control circuitry  20  to send a duty cycle change request (e.g., a duty cycle increment or a duty cycle decrement command) to device  12 . 
     As shown in  FIG. 13 , a duty cycle setting for system  8  is selected at block  120 . During the operations of block  120 , control circuitry  20  uses wireless communications circuitry to wirelessly send a duty cycle change request for the selected duty cycle to the wireless communications circuitry of control circuitry  42 . 
     During the operations of blocks  122 ,  124 , and  126 , device  10  sweeps the value of the current flowing between circuit  80  and  86  (current Iout=Iref) between first and second current values. The current is adjusted by controlling the current draw of circuitry  86  using control circuitry  20 . While the current is swept across multiple different values, control circuitry  20  uses sensing circuitry such as current sensor  82  and voltage sensor  84  to monitor the output power Pout from circuitry  80  and to identify any peaks in Pout (as a function of current) of the type shown in  FIG. 7 . 
     At block  122 , device  10  adjusts reference current Iref to battery charger circuitry  86 , thereby adjusting Iout flowing between rectifier circuitry  80  and battery charger circuitry  86 . The output power Pout resulting from this adjustment is measured at block  124 . In particular, sensors  82  and  84  gather Iout and Vout measurements, which control circuitry  20  multiplies together to determine Pout (the power flowing from rectifier circuitry  80  into the load of device  10  (battery charger circuitry  86  and battery  18 ). As indicated by block  126  and line  128 , the value of Iref is incrementally adjusted to sweep across a range of Iref values until a peak is detected. As an example, Iref may be swept across a range of Iref values to detect peak PK of the 20% duty cycle curve of  FIG. 7 . 
     During the operations of block  130 , control circuitry determines whether the peak value of Pout is sufficient to satisfy the amount of power currently desired by battery charger circuitry  86 . If the currently desired power level can be satisfied at the currently selected duty cycle, that duty cycle may be considered to be the maximum duty cycle that satisfies the desired power level while exhibiting a peak power. The operating duty cycle can then be maintained at this maximum value or set just above this maximum value (e.g., to a higher duty cycle that is a step above this maximum value). Processing can then proceed to block  134 . If the currently desired power level cannot be satisfied at the currently selected duty cycle (e.g., if peak PK of  FIG. 7  is below the desired power level for circuitry  86 ), processing can loop back to block  120  as indicated by line  132  so that a larger trial duty cycle can be established. 
     Once the operations of block  130  determine that for a given duty cycle the demanded load power has been satisfactorily provided at the peak, control circuitry  20  can conclude that the current duty cycle corresponds to the minimum duty cycle that can deliver the desired power to the load (the load power loop is complete). Processing can then proceed to block  134 . 
     During the operations of block  134 , control circuitry  20  determines whether any change has been made to the desired load power. For example, the desired load power may decrease if battery  18  becomes fully charged or may increase if additional components are used that drain battery  18 . If the load power has changed, processing loops back to block  120 , as indicated by line  136 . 
     If the load power has not changed, processing can proceed to the peak efficiency point loop to fine tune inverter duty cycle to maximize system efficiency. In particular, processing can proceed to block  138 . During the operations of block  138 , control circuitry  20  determines whether the peak efficiency (Eff of  FIGS. 5 and 6 ) has been reached. If not, control circuitry  20  can adjust the duty cycle by sending an appropriate duty cycle change request to device  12  at block  140 . Processing can then loop back to block  134 , as indicated by line  142 . If the peak efficiency has been reached, the operations of block  140  can be omitted. 
     The foregoing is 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: 20180130
Publication Date: 20210413
Grant Date: 20210413
Priority Date: 20170202
Inventors: QIU, WEIHONG
DAYAL, ROHAN
MOUSSAOUI, ZAKI
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J7/00045", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/402", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00045", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/0037", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/40", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B5/0075", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B5/24", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B5/79", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/79", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/24", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 62980795