Dynamic capacitance tuning for wireless power transfer

Abstract

To provide an invention pertaining to dynamic capacitance tuning for wireless power transfer.SOLUTION: A method for operating a wireless power transmitter including a wireless power transmitting coil, an inverter that receives an input voltage and generates an AC output voltage that drives the wireless power transmitting coil, and at least one adjustable capacitance coupled to the wireless power transmitting coil to form a series tuning circuit therewith, can be performed by a control circuit of the wireless power transmitter. The method includes determining, in response to increased power demand from a wireless power receiver, whether the input voltage is at a maximum value and, if so, reducing the at least one adjustable capacitance to increase gain, or determining, in response to decreased power demand from the wireless power receiver, whether the input voltage is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease gain.SELECTED DRAWING: None

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 585,279, entitled "Dynamic Capacitance Tuning For Wireless Power Transfer", filed September 26, 2023, U.S. Patent Application No. 18 / 529,564, entitled "Dynamic Capacitance Tuning For Wireless Power Transfer", filed December 5, 2023, and U.S. Patent Application No. 18 / 613,196, entitled "Dynamic Capacitance Tuning For Wireless Power Transfer", filed March 22, 2024, each of which is incorporated by reference in its entirety for all purposes. [Background technology]

[0002] Wireless power transfer is becoming increasingly prevalent in a wide variety of electronic devices. For example, many electronic devices, such as smartphones, tablet computers, smart watches, wireless earbuds, styluses, etc., may employ wireless power transfer to facilitate charging of batteries within the device. In some applications, higher levels of wireless power transfer may be desired, for example, to provide faster charging. Such higher power transfer levels may benefit from techniques for adjusting various system parameters to improve operating efficiency, voltage regulation, etc. Summary of the Invention

[0003] The wireless power transmitter comprises a wireless power transmitting coil, an inverter that receives an input voltage and generates an AC output voltage that drives the wireless power transmitting coil, at least one adjustable capacitance coupled to the wireless power transmitting coil to form a series tuned circuit with the wireless power transmitting coil, and a control circuit that operates the inverter and the at least one adjustable capacitance to supply wireless power to the wireless power receiver, wherein the control circuit responds to a power demand from the wireless power receiver by determining whether the input voltage is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase a gain, or determining whether the input voltage is at a minimum value and, if so, responding to a power demand from the wireless power receiver by increasing the at least one adjustable capacitance to decrease the gain.

[0004] The at least one adjustable capacitance may include one or more capacitors selectively coupleable to the wireless power transmitting coil by one or more switches controlled by the control circuit. The at least one adjustable capacitance may include at least one capacitor coupled to the wireless power transmitting coil and at least two capacitors selectively coupleable to the wireless power transmitting coil by one or more switches controlled by the control circuit. Determining whether the input voltage is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase the gain may further include at least temporarily adjusting the input voltage before decreasing the at least one adjustable capacitance. Adjusting the input voltage at least temporarily before decreasing the at least one adjustable capacitance may be responsive to an operating power level of the wireless power transmitter. Determining whether the input voltage is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease the gain may further include at least temporarily adjusting the input voltage before increasing the at least one adjustable capacitance. Adjusting the input voltage at least temporarily before increasing the at least one adjustable capacitance is responsive to an operating power level of the wireless power transmitter.

[0005] The wireless power transmitter may further include a control circuit that increases at least one adjustable capacitance in response to the one or more hard switching events to mitigate the hard switching events. The at least one adjustable capacitance may include one or more capacitors selectively coupleable between the inverter output and the wireless power transmit coil by one or more first switches controlled by the control circuit and one or more capacitors selectively coupleable between the inverter output and ground by one or more second switches controlled by the control circuit. The one or more capacitors selectively coupleable between the inverter output and the wireless power transmit coil may include at least one capacitor coupled between the inverter output and the wireless power transmit coil and at least two capacitors selectively coupleable between the inverter output and the wireless power transmit coil by the one or more first switches. The one or more capacitors selectively coupleable between the inverter output and ground may include at least one capacitor coupled between the inverter output and ground and a plurality of capacitors selectively coupleable between the inverter output and ground by one or more second switches. The wireless power transmitter may further include a control circuit that, in response to the absence of the one or more hard switching events, decreases the at least one adjustable capacitance to mitigate the hard switching events.

[0006] A method of operating a wireless power transmitter having a wireless power transmitting coil, an inverter that receives an input voltage and generates an AC output voltage that drives the wireless power transmitting coil, and at least one adjustable capacitance coupled to the wireless power transmitting coil to form a series-tuned circuit with the wireless power transmitting coil may be performed by a control circuit of the wireless power transmitter and includes: in response to an increase in power demand from the wireless power receiver, determining whether the input voltage is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase gain, or in response to a decreased power demand from the wireless power receiver, determining whether the input voltage is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease gain.

[0007] Determining whether the input voltage is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase the gain may further include at least temporarily adjusting the input voltage before decreasing the at least one adjustable capacitance. Determining whether the input voltage is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease the gain may further include at least temporarily adjusting the input voltage before increasing the at least one adjustable capacitance.

[0008] The method may further include, in response to the one or more hard switching events, increasing the at least one adjustable capacitance to mitigate the hard switching events, and in response to the absence of the one or more hard switching events, decreasing the at least one adjustable capacitance to mitigate the hard switching events.

[0009] The wireless power receiver includes a wireless power receiving coil, a rectifier that receives an AC voltage induced in the wireless power receiving coil by the wireless power transmitter and generates a DC output voltage therefrom, at least one adjustable capacitance coupled to the wireless power receiving coil to form a series tuned circuit with the wireless power receiving coil, and a control circuit that operates the rectifier and the at least one adjustable capacitance to supply power to a load coupled to the DC output voltage of the rectifier. The control circuit can respond to a power demand by determining whether a DC input voltage of an inverter of the wireless power transmitter is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase a gain, or determining whether a DC input voltage of the inverter of the wireless power transmitter is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease a gain. The DC input voltage can be determined by the control circuit in response to one or more messages received from the wireless power transmitter.

[0010] The at least one adjustable capacitance may include one or more capacitors selectively coupleable to the wireless power receiving coil by one or more switches controlled by the control circuit. The at least one adjustable capacitance may include at least one capacitor coupled between the wireless power receiving coil and the rectifier, and at least one capacitor selectively coupleable between the wireless power receiving coil and the rectifier by one or more switches controlled by the control circuit.

[0011] Determining whether the DC input voltage of the inverter is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase the gain may further include at least temporarily decreasing the rectifier power before decreasing the at least one adjustable capacitance in response to the rectifier power. Determining whether the DC input voltage of the inverter is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease the gain may further include at least temporarily decreasing the rectifier power before increasing the at least one adjustable capacitance in response to the rectifier power.

[0012] A method of operating a wireless power receiver having a wireless power receiving coil, a rectifier that receives an AC voltage induced in the wireless power receiving coil by a wireless power transmitter and generates a DC output voltage therefrom, and at least one adjustable capacitance coupled to the wireless power receiving coil to form a series tuned circuit with the wireless power receiving coil may be performed by a control circuit in the wireless power receiver and may include determining whether a DC input voltage of an inverter of the wireless power transmitter is at a maximum value in response to an increase in power demand, and if so, decreasing the at least one adjustable capacitance to increase gain, or determining whether a DC input voltage of the inverter of the wireless power transmitter is at a minimum value in response to a decreased power demand, and if so, increasing the at least one adjustable capacitance to decrease gain. The DC input voltage is determined by the control circuit in response to one or more messages received from the wireless power transmitter.

[0013] Determining whether the DC input voltage of the inverter is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase the gain may further include at least temporarily decreasing the rectifier power before decreasing the at least one adjustable capacitance in response to the rectifier power. Determining whether the DC input voltage of the inverter is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease the gain may further include at least temporarily decreasing the rectifier power before increasing the at least one adjustable capacitance in response to the rectifier power. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 shows a simplified block diagram of a wireless power transfer system.

[0015] [Figure 2A] 1 shows a schematic diagram of a wireless power transfer system. [Figure 2B] 1 shows a schematic diagram of a wireless power transfer system. [Figure 2C] 1 shows a schematic diagram of a wireless power transfer system. [Figure 2D] 1 shows a schematic diagram of a wireless power transfer system. [Figure 2E] 1 shows a schematic diagram of a wireless power transfer system.

[0016] [Figure 3A] 1 shows a flow chart of a wireless power transmitter capacitance tuning technique. [Figure 3B] 1 shows a flow chart of a wireless power transmitter capacitance tuning technique. [Figure 3C] 1 shows a flow chart of a wireless power transmitter capacitance tuning technique.

[0017] [Figure 4] 1 shows a flowchart of a capacitance tuning technique for a wireless power receiver. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the following description, for the sake of convenience, numerous specific details are set forth to enhance the understanding of the disclosed concepts. As part of this description, some of the drawings in the present disclosure represent structures and devices in block diagram form to avoid obscuring the present invention. For the sake of clarity, not all features of an actual implementation are described herein. Moreover, the language used in this specification has been selected solely for purposes of readability and explanation, and not to limit or restrict the disclosed subject matter. Rather, the appended claims are intended for such purposes.

[0019] Various embodiments of the disclosed concepts are illustrated in the accompanying drawings, by way of example and not by way of limitation, in which like reference numerals refer to like elements. For simplicity and clarity of illustration, where considered appropriate, reference numerals have been repeated in different drawings to indicate corresponding and / or similar elements. In addition, numerous specific details have been described to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the relevant associated functions being described. References to "an", "one", or "another" embodiment in the present disclosure are not necessarily to the same or different embodiments, but rather to at least one. A given drawing is used to illustrate multiple embodiments of the present disclosure or multiple species of the present disclosure, and not all elements in the drawing may be required in a given embodiment or species. A reference numeral, when provided in a given drawing, may refer to the same element throughout the several drawings, but may not be repeated in all drawings. The drawings are not to scale unless otherwise indicated and the proportions of certain parts may be exaggerated to better show the details and features of the present disclosure.

[0020] FIG. 1 shows a simplified block diagram of a wireless power transfer system 100. The wireless power transfer system includes a power transmitter (PTx) 110 that transmits power wirelessly, such as via inductive coupling 130, to a power receiver (PRx) 120. The power transmitter 110 can receive input power that is converted to an AC voltage having specific voltage and frequency characteristics by an inverter 114. The inverter 114 can be controlled by a controller / communication module 116 that operates as described further below. In various embodiments, the inverter controller and communication module may be implemented in a common system, such as a system based on a microprocessor, microcontroller, or the like. In other embodiments, the inverter controller may be implemented by a separate controller module and communication module with means of communication therebetween. The inverter 114 may be constructed using any suitable circuit topology (e.g., full bridge, half bridge, etc.) and may be implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc., made using silicon, silicon carbide, or gallium nitride devices).

[0021] The inverter 114 can deliver the generated AC voltage to the transmitter coil 112. In addition to the wireless coil that allows for magnetic coupling to the receiver, the transmitter coil block 112 shown in FIG. 1 may include tuning circuit components, such as additional inductors and capacitors, that facilitate operation of the transmitter in different conditions, such as different degrees of magnetic coupling to the receiver, different operating frequencies, etc. The wireless coil itself can be configured in a variety of different ways. In some embodiments, the wireless coil can be formed as a winding of wire wound around a suitable bobbin. In other embodiments, the wireless coil can be formed as a trace on a printed circuit board. Other arrangements are possible and can be used in conjunction with the various embodiments described herein. The wireless transmitter coil can also include a core of magnetically permeable material (e.g., ferrite) configured to affect the magnetic flux pattern of the coil in a manner suitable for a particular application. The teachings herein can be applied in conjunction with any of a wide variety of transmitter coil arrangements suitable for a given application.

[0022] The PTx controller / communication module 116 can monitor the power transmission coil and use information derived therefrom to control the inverter 114 as appropriate for a given situation. For example, the controller / communication module can be configured to operate the inverter 114 at a given frequency or output voltage depending on a particular application. In some embodiments, the controller / communication module can be configured to receive information from the PRx device and control the inverter 114 accordingly. This information may be received via the power transmission coil (i.e., in-band communication) or may be received via a separate communication channel (not shown, i.e., out-of-band communication). In the case of in-band communication, the controller / communication module 116 can detect and decode signals (such as voltage, frequency, or load changes) imposed by the PRx on the magnetic link to receive information, and can command the inverter to modulate the delivered power by manipulating various parameters (such as voltage, frequency, etc.) of the generated voltage to transmit information to the PRx. In some embodiments, the controller / communication module may be configured to employ Frequency Shift Keying (FSK) communication, in which the frequency of the inverter signal is modulated, to communicate data to the PRx. The controller / communication module 116 may be configured to detect Amplitude Shift Keying (ASK) or load modulation based communication from the PRx. In either case, the controller / communication module 126 may be configured to vary the current drawn at the receiver to manipulate the waveform seen on the Tx coil to deliver information from the PRx to the PTx. For out-of-band communication, additional modules may be provided to enable communication between the PTx and PRx, such as WiFi, Bluetooth, or other wireless links, or any other suitable communication channel.

[0023] As mentioned above, the controller / communications module 116 may be, for example, a single module provided on a single integrated circuit, or may be constructed from multiple modules / devices provided on different integrated circuits, or a combination of integrated circuits and discrete circuits having both analog and digital components. The teachings herein are not limited to any particular arrangement of controller / communications circuitry.

[0024] The PTx device 110 may optionally include other systems and components, such as a separate communications module 118. In some embodiments, the communications module 118 may communicate with a corresponding module in the PTx via a power transmission coil. In other embodiments, the communications module 118 may communicate with a corresponding module using a separate physical channel 138.

[0025] As mentioned above, the wireless power transmission system also includes a wireless power receiver (PRx) 120. The wireless power receiver may include a receiver coil 122 that may be magnetically coupled 130 to the transmitter coil 112. Similar to the transmitter coil 112 described above, the receiver coil block 122 shown in FIG. 1 may include tuning circuit components such as additional inductors and capacitors to facilitate operation of the transmitter in different conditions, such as different degrees of magnetic coupling to the receiver, different operating frequencies, etc. The wireless coil itself may be configured in a variety of different ways. In some embodiments, the wireless coil may be formed as a winding of wire wound around a suitable bobbin. In other embodiments, the wireless coil may be formed as a trace on a printed circuit board. Other arrangements are possible and may be used in conjunction with the various embodiments described herein. The wireless receiver coil may also include a core of magnetically permeable material (e.g., ferrite) configured to affect the magnetic flux pattern of the coil in a manner suitable for a particular application. The teachings herein may be applied in conjunction with any of a wide variety of receiver coil arrangements suitable for a given application.

[0026] The receiver coil 122 outputs an AC voltage induced therein by magnetic induction through the transmitter coil 112. This output AC voltage may be provided to a rectifier 124 that provides DC output power to one or more loads associated with the PRx device. The rectifier 124 may be controlled by a controller / communication module 126 that operates as described further below. In various embodiments, the rectifier controller and communication module may be implemented in a common system, such as a system based on a microprocessor, microcontroller, or the like. In other embodiments, the rectifier controller may be implemented by a separate controller module and communication module having means of communication therebetween. The rectifier 124 may be constructed using any suitable circuit topology (e.g., full bridge, half bridge, etc.) and may be implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc., fabricated using silicon, silicon carbide, or gallium nitride devices).

[0027] The PRx controller / communication module 126 can monitor the receiver coil and use information derived therefrom to appropriately control the rectifier 124 for a given situation. For example, the controller / communication module can be configured to operate the rectifier 124 to provide a given output voltage for a particular application. In some embodiments, the controller / communication module can be configured to transmit information to the PTx device to effectively control the power delivered to the receiver. This information may be received or transmitted via the power transmission coil (i.e., in-band communication) or may be transmitted via a separate communication channel (not shown, i.e., out-of-band communication). In the case of in-band communication, the controller / communication module 126 can, for example, modulate the load current or other electrical parameters of the received power to transmit information to the PTx. In some embodiments, the controller / communication module 126 can be configured to detect and decode signals (such as voltage, frequency, or load variations) applied by the PTx to the magnetic link in order to receive information from the PTx. In some embodiments, the controller / communication module 126 may be configured to receive frequency shift keying (FSK) communications, where the frequency of the inverter signal is modulated to communicate data to the PRx. The controller / communication module 126 may be configured to generate amplitude shift keying (ASK) communications or load modulation based communications from the PRx. In either case, the controller / communication module 126 may be configured to vary the current drawn at the receiver to manipulate the waveform seen on the Tx coil to deliver information from the PRx to the PTx. For out-of-band communications, additional modules may be provided that enable communication between the PTx and PRx, such as WiFi, Bluetooth, or other wireless links, or any other suitable communication channel.

[0028] As mentioned above, the controller / communication module 126 may be, for example, a single module provided on a single integrated circuit, or may be comprised of multiple modules / devices provided on different integrated circuits, or a combination of integrated circuits and discrete circuits having both analog and digital components. The teachings herein are not limited to any particular arrangement of controller / communication circuitry. The PRx device 120 may optionally include other systems and components, such as a communications ("comms") module 128. In some embodiments, the communications module 128 may communicate with a corresponding module in the PTx via the power transmission coil. In other embodiments, the communications module 128 may communicate with a corresponding module or tag using a separate physical channel 138.

[0029] Many variations and extensions of the wireless power transmission system 100 described above are possible, and the teachings below are applicable to any such variations and extensions.

[0030] 2A-2E show schematic diagrams of a wireless power transfer system. FIG. 2A shows an overall schematic diagram 200 of a wireless power transfer system including a wireless power transmitter (PTx) 210 and a wireless power receiver 220, such as those with similar reference numbers (e.g., PTx 110 and PRx 120) described above with respect to FIG. 1. The wireless power transmitter 210 may include an inverter 114 that may drive a transmitter coil 112. The inverter 114 is shown as a full-bridge inverter, although other inverter configurations may be used depending on the requirements of the application. The inverter 114 may receive an input voltage Vin from an input voltage source represented by a capacitor Cin, which may include any suitable DC power source, such as a battery, a DC-DC converter, an AC-DC converter, etc. The inverter 114 may drive the transmitter coil 112 via a series tuned network 231, which will be described in more detail below with respect to FIG. 2B. Also shown in Figure 2A is an optional slew rate tuning circuit 233, which is described in more detail below with respect to Figure 2D. Figure 2B also shows parasitic elements 239, which can represent the effects of various wireless charger system implementations, such as capacitance associated with wires / cords, etc. The depicted representation is only an example, and other representations may be more appropriate depending on the exact physical configuration of a particular implementation.

[0031] FIG. 2A also shows a wireless power receiver 220. The wireless power receiver 220 may include a rectifier that can drive a receiver coil 122 that can have a current induced therein by the transmitter coil 112. The rectifier 124 is shown as a full-bridge rectifier, although other rectifier configurations may be used depending on the requirements of the application. The rectifier 124 can generate an output voltage Vrect / Vout from an AC voltage appearing across the receiver coil 122. The rectifier 124 can be driven via a series tuned circuit 235, which will be described in more detail below with respect to FIG. 2C. Also shown in FIG. 2A is an in-band communication circuit 237, which will be described in more detail below with respect to FIG. 2E.

[0032] 2B shows a schematic diagram of the wireless power transmitter series tuned circuit 231 introduced above with reference to FIG. 2A. The transmitter series tuned circuit may include capacitances such as capacitors Ctx1, Ctx2, and Ctx3 along with the inductance of the transmitter coil 112. Depending on various parameters such as the amount of power to be transmitted, the operating voltage, the degree of coupling between PTx and PRx, it may be desirable to adjust the series tuned circuit to improve overall operation. For example, as described in more detail below, it may be desirable to adjust the series tuned circuit to vary the gain of the wireless power transmission system to enable adaptation to different input voltages, power levels, etc.

[0033] The series tuned circuit 231 may include a base capacitance of capacitor Ctx1 that may always be present in the series tuned circuit, and selectable capacitances from capacitors Ctx2 and Ctx3. These capacitors may be selectively connected in parallel with capacitor Ctx1 to increase the effective capacitance by closing switches Qctx2 and / or Qctx3, respectively. Correspondingly, when one or more of switches Qctx2 and Qctx3 are closed to connect the corresponding capacitor to the series tuned circuit, opening such switch may decrease the capacitance of the series tuned circuit. A range of capacitances may be provided by selecting different values ​​for each capacitor. Switches Qctx2 and Qctx3 may be controlled by the wireless power transmitter controller / communication circuit 116 described above with respect to FIG. 1. Such control may implement one or more of the control techniques described below with respect to FIGS. 3A-3C. The configuration of FIG. 2B is merely exemplary, and other configurations including additional selective capacitors, all selectable capacitors, series combinations of capacitors (to selectively reduce capacitance), etc. may all be implemented as appropriate for a given application.

[0034] 2C shows a schematic diagram of the wireless power receiver series tuned circuit 235 introduced above with reference to FIG. 2A. The receiver series tuned circuit may include capacitances, such as capacitors Crx1 and Crx2, along with the inductance of the receiver coil 122. Depending on various parameters, such as the amount of power to be transferred, the operating voltage, the degree of coupling between PTx and PRx, it may be desirable to adjust the series tuned circuit to improve overall operation. For example, as described in more detail below, it may be desirable to adjust the series tuned circuit to vary the gain of the wireless power transfer system to allow adaptation to different input voltages, power levels, etc.

[0035] The series tuning circuit 235 may include a base capacitance of the capacitor Crx1 that may always be present in the series tuning circuit, and a selectable capacitance from the capacitor Crx2. This capacitor may be selectively connected in parallel with the capacitor Ctx1 to increase the effective capacitance by closing a switch Qcrx2. Correspondingly, when the switch Qcrx2 is closed and connects the corresponding capacitor to the series tuning circuit, the capacitance of the series tuning circuit may be decreased by opening such switch. A range of capacitances may be provided by selecting different values ​​for each capacitor. The switch Qcrx2 may be controlled by the wireless power receiver controller / communication circuit 126 described above with respect to FIG. 1. Such control may implement a control technique as described below with respect to FIG. 4. The configuration of FIG. 2C is merely exemplary, and other configurations including additional selective capacitors, all selectable capacitors, series combinations of capacitors (to selectively reduce capacitance), etc. may all be implemented as appropriate for a given application.

[0036] FIG. 2D illustrates the optional slew rate tuning circuit 233 introduced above with respect to FIG. 2A. For improved operating efficiency, it may be preferable to operate the inverter 114 in zero voltage switching (ZVS), which may reduce switching losses associated with inverter operation. Depending on various parameters such as operating voltage, operating power level, etc., ZVS may not be possible for a given inverter circuit configuration, including but not limited to the overall capacitance coupled to the inverter. To enable ZVS over a wider operating range, the slew rate tuning circuit 233 may be provided. More specifically, if one or more hard switching events (i.e., lack of ZVS) are detected, the capacitance may be decreased. Alternatively, if no hard switching events are detected for a given period of time (which may correspond to a larger than required ZVS margin), the capacitance may be increased, thereby increasing the voltage slew rate of the inverter.

[0037] The slew rate tuning circuit may include a base capacitance of capacitor Csw1 that may always be present, and selectable capacitances from capacitors Csw2, Csw3, and Csw4. These capacitors may be selectively connected in parallel with capacitor Csw1 to increase the effective capacitance by closing switches Qcsw2, Qcsw3, and Qcsw4. Correspondingly, when one or more of switches Qcrx2 are closed to connect the corresponding capacitor to the series tuning circuit, opening such switch may decrease the capacitance of the series tuning circuit. A corresponding slew rate capacitor and associated switch may be connected to each inverter leg as shown in FIG. 2A. A range of capacitances may be provided by selecting different values ​​for each capacitor. Switches Qcsw2, Qcsw3, and Qcsw4 may be controlled by the wireless power transmitter controller / communication circuit 116 described above with respect to FIG. 1. Such control may implement various control techniques depending on the implementation. In some embodiments, the slew rate capacitance may be adjusted with changes to the series tuning capacitance, as described in more detail below. The configuration of Figure 2D is merely exemplary, and other configurations including additional selective capacitors, all selectable capacitors, series combinations of capacitors (to selectively reduce capacitance), etc. may all be implemented as appropriate for a given application.

[0038] FIG. 2E illustrates the in-band communication circuit 237 introduced above with respect to FIG. 2A. The in-band communication circuit 237 is only one example of a wide variety of in-band communication circuit types associated with corresponding in-band communication methods. In many embodiments, various forms of load modulation can be used. Such load modulation can be used to implement amplitude switch keying ("ASK") communication, in which the connection or disconnection of an additional load element can be used to vary the received power, which can be detected by the transmitter for a corresponding change in the transmitted power. As an example, the in-band communication circuit 237 includes switches Qcc1 and Qcc2 that can selectively couple / decouple capacitors Ccomm1 and Ccomm2 to / from respective legs of the (full-bridge) rectifier 124, represented in FIG. 2E by switches 224a and 224b. This configuration is only one example, and many other configurations of such circuits can be implemented.

[0039] 3A-3C show a flow chart of a wireless power transmitter capacitance tuning technique. The PTx input voltage Vin (FIG. 2A) can be varied to adjust the output power of the inverter and therefore the power supplied to the wireless power receiver. Increasing the input voltage Vin can increase the delivered power and vice versa. Thus, the wireless power transmitter can adjust the delivered power by varying the input voltage Vin, for example by modifying the control signal provided to the DC-DC converter that supplies the input voltage. Depending on the output voltage provided as Vin and the power level being requested by the wireless power receiver, the system may end up operating in a region where it becomes difficult or impossible to adjust the output voltage to the desired level. This can be overcome in at least some conditions by adjusting the series tuning capacitance, for example using a circuit as described above with reference to FIGS. 2A-2B.

[0040] FIG. 3A shows a flow chart 300a of a high-level wireless power transmitter capacitance tuning technique. Starting at block 341, the transmitter controller (e.g., controller / communication circuitry 116) can determine whether the input voltage Vin has reached a maximum value (i.e., a high threshold). This can occur, for example, in response to a request for increased power from the wireless power receiver when the wireless power transmitter is already operating at its maximum input voltage. If so, the controller can decrease Ctx to increase the gain of the wireless power transmission system (block 342) while continuing to monitor the input voltage. Decreasing Ctx can be accomplished, for example, by opening one or more of the switches Qctx2, Qctx3 (FIG. 2B) to disconnect one or more of the selectable capacitors Ctx2, Ctx3 coupled to the transmitter coil. If the transmitter controller determines in block 341 that the input voltage is not at the maximum / high threshold, the controller can determine in block 343 whether the input voltage has reached a minimum value (i.e., a low threshold). This may be done, for example, in response to a decrease in transmitted wireless power or a request to decrease transmitted wireless power. If so, the controller may increase Ctx to decrease the gain of the wireless power transfer system while continuing to monitor the input voltage (block 344). Increasing Ctx may be accomplished, for example, by closing one or more of switches Qctx2, Qctx3 (FIG. 2B) to couple one or more of selectable capacitors Ctx2, Ctx3 to the transmitter coil. Thus, the transmitter controller may adjust or regulate the input voltage as well as the series tuning capacitance in response to the power demand from the wireless power receiver.

[0041] As mentioned above, different capacitance values ​​can be achieved by different combinations of capacitors Ctxn. Furthermore, different numbers of resonant capacitors Ctxn can be provided, and each capacitor can have a different capacitance value (or the same capacitance value). Thus, the system can be designed to provide any of a range of capacitance values ​​in response to an input voltage.

[0042] FIG. 3B shows a flowchart 300b of a modified wireless power transmitter capacitance tuning technique with an optional additional step that may be advantageous in various conditions, such as relatively high transmit power levels. As before, in block 341, the transmitter controller (e.g., controller / communication circuitry 116) can determine whether the input voltage Vin has reached a maximum value (i.e., high threshold), e.g., in response to an increase in power demand from the wireless power receiver. If so, the controller can first adjust (e.g., reduce) Vin (block 345a) and possibly at least temporarily reduce the transmitted power level before making any changes to the series tuning capacitance. Adjusting the input voltage before changing the input capacitance can prevent overvoltage events from occurring at the wireless power receiver due to transmitter-side capacitance changes. The controller can then decrease Ctx to increase the gain of the wireless power transmission system while continuing to monitor the input voltage (block 342). As explained above, decreasing Ctx may be accomplished by, for example, opening one or more of the switches Qctx2, Qctx3 (FIG. 2B) to disconnect one or more of the selectable capacitors Ctx2, Ctx3 coupled to the transmitter coil. The transmitted power level may then be increased again to a relatively high value, for example, if a higher power level is requested by the wireless power receiver.

[0043] Alternatively, if the transmitter controller determines in block 341 that the input voltage is not at a maximum / high threshold, the controller may determine in block 343 whether the input voltage has reached a minimum (i.e., low threshold), e.g., in response to a decrease in power demand by the wireless power receiver. If so, the controller may (optionally) first adjust Vin (block 345b) and possibly at least temporarily reduce the transmitted power level before making any changes to the series-tuned capacitance. As explained above, adjusting the input voltage (and associated transmit power level) before changing the input capacitance may prevent an overvoltage event from occurring at the wireless power receiver due to a capacitance change on the transmitter side. The controller may then increase Ctx to decrease the gain of the wireless power transfer system while continuing to monitor the input voltage (block 344). Increasing Ctx may be accomplished, for example, by closing one or more of the switches Qctx2, Qctx3 (FIG. 2B) to couple one or more of the selectable capacitors Ctx2, Ctx3 to the transmitter coil. Then, for example, if a higher power level is requested by the wireless power receiver, the transmitted power level may be increased again to a relatively high value.

[0044] The input voltage regulation discussed above can be achieved in a variety of ways. For example, in at least some embodiments, voltage regulation may be achieved by modifying a feedback control signal provided to a DC-DC converter or other regulator that provides Vin. In other embodiments, such as those in which the input voltage is provided by a USB-PD power adapter, appropriate USB-PD control signals can be provided to the adapter to modify the voltage provided.

[0045] As explained above, certain operating regimes, e.g., higher power levels, may require input voltage regulation before making transmitter side capacitance changes, while other operating regimes, e.g., lower transmit power levels, may not necessarily benefit from such operation. Thus, the techniques described above can be modified to selectively provide input voltage regulation before switching the capacitors in response to the transmitted power level. As an example, the input voltage regulation function can be enabled in response to the power level rising above a first threshold power level and disabled in response to the power level falling below a second threshold power level. The first and second threshold power levels may be the same value or different values, providing some hysteresis in operation.

[0046] 3C shows a flowchart 300c of a further modified wireless power transmitter capacitance tuning technique with an optional additional step that may be advantageous to address inverter hard switching (i.e., non-ZVS) events that may lead to increased losses and reduced operating efficiency. Starting at block 346, the control circuitry may determine whether a hard switching condition exists. This may be the occurrence of a single hard switching event, or more preferably, in at least some cases, the detection of multiple hard switching events within a period of time and / or multiple consecutive hard switching events. Such hard switching events may indicate an opportunity to improve operating efficiency by increasing the capacitance coupled to the inverter, which may include either adjusting the series tuning capacitance Ctx and / or adjusting the optional slew rate tuning capacitance, as described above with respect to FIG. 3D.

[0047] In either case, if a hard switching condition is detected, the controller can increase the series tuned capacitance (block 347) or adjust both the slew rate capacitance Csw and the series tuned capacitance Ctx to provide an overall increase in capacitance. For example, the adjustments may include increasing the slew rate capacitance Csw and decreasing the series tuned capacitance Ctx while still providing an overall increase in capacitance. Additionally (and potentially optionally), the controller can adjust the input voltage Vin before changing the capacitance (block 345c) to prevent a receiver-side overvoltage event (as described above). Although not shown in FIG. 3C, there is a procedure for decreasing the capacitance if the condition leading to the capacitance triggered by the preceding hard switching no longer exists. Such a change can be made, for example, by detecting that a hard switching event has not been detected for a period of time. The system can then decrease the capacitance (by adjusting the series tuned capacitance Ctx and / or the slew rate capacitance Csw). If the reduction triggers a hard switching event, the capacitance adjustment can be reversed (i.e., the capacitance is increased again). Alternatively, the capacitance reduction may be maintained if the reduction does not trigger a hard switching condition.

[0048] Otherwise, if a hard switching condition does not trigger the capacitance adjustment in block 346, the technique illustrated in flow chart 300c may be similar to that described above with reference to FIGS. 3A and 3B. As before, in block 341, the transmitter controller (e.g., controller / communication circuitry 116) may determine whether the input voltage Vin has reached a maximum value (i.e., a high threshold), e.g., in response to an increase in power demand from the wireless power receiver. If so, the controller may first adjust (e.g., reduce since it is already at a maximum voltage) Vin (e.g., in response to the transmitted power level) (block 345a) and may also at least temporarily reduce the transmitted power level before making any changes to the series tuned capacitance. Adjusting (e.g., reducing) the input voltage before changing the input capacitance may prevent an overvoltage event from occurring at the wireless power receiver due to a capacitance change on the transmitter side. The controller may then decrease Ctx to increase the gain of the wireless power transfer system while continuing to monitor the input voltage (block 342). As explained above, decreasing Ctx may be accomplished by, for example, opening one or more of the switches Qctx2, Qctx3 (FIG. 2B) to disconnect one or more of the selectable capacitors Ctx2, Ctx3 coupled to the transmitter coil. The transmitted power level may then be increased again to a relatively high value, for example, if a higher power level is requested by the wireless power receiver.

[0049] Alternatively, if the transmitter controller determines in block 341 that the input voltage is not at a maximum / high threshold, the controller may determine in block 343 whether the input voltage has reached a minimum (i.e., low threshold), e.g., in response to a reduced power demand from the wireless power receiver. If so, the controller may first adjust Vin (e.g., increase it since it is already at a minimum voltage) (block 345b) (optionally, e.g., in response to the transmitted power level) and potentially temporarily reduce the transmitted power level before making any changes to the series-tuned capacitance. As explained above, adjusting (increasing) the input voltage (and associated transmit power level) before changing the input capacitance may prevent an overvoltage event from occurring at the wireless power receiver due to a capacitance change on the transmitter side. The controller may then increase Ctx to reduce the gain of the wireless power transfer system while continuing to monitor the input voltage (block 344). Increasing Ctx may be accomplished, for example, by closing one or more of the switches Qctx2, Qctx3 (FIG. 2B) to couple one or more of the selectable capacitors Ctx2, Ctx3 to the transmitter coil. The transmitted power level may then be increased again to a relatively high value, for example, if a higher power level is requested by the wireless power receiver.

[0050] Above, various techniques have been described for adjusting the wireless power transmitter series tuning capacitance according to the input voltage and load conditions to achieve improved voltage regulation. Additionally or alternatively, the series tuning capacitance adjustment can also be performed at the wireless power receiver side to achieve a similar effect. FIG. 4 shows a flow chart of a wireless power receiver capacitance tuning technique 400 in which a receiver side resonant gain associated with a receiver side resonant circuit including a receiver coil and a series tuning capacitance Crx is adjusted based on a power level and a transmitter side input voltage. Starting at block 451, a receiver controller (e.g., receiver controller / communication circuit 126) can determine whether increased power is needed or desired. If so, at block 452, the receiver controller can send an increased power request (PTx) to the wireless power transmitter. If PTx can transmit an increased power level, PTx can transmit, for example, by increasing its input voltage Vin. If instead the PTx is unable to transmit an increased power level, it can communicate this to the wireless power receiver, for example, by transmitting a NAK (negative acknowledgement) message in response to a request from the receiver for increased power. This NAK message (and any preceding messages from the receiver requesting increased power) can follow one or more standard protocols, such as the Qi wireless charging standard promulgated by the Wireless Power Consortium, or can be in any other format suitable for communication between the PTx and the PRx, such as a proprietary protocol.

[0051] If a NAK message is not received (block 453), the power is increased by PTx, and the process may return to block 451. If, instead, a NAK message is received (block 453), the receiver controller may determine whether PTx is unable to transmit the increased power because PTx is already at its maximum input voltage Vin. For example, the NAK message received from PTx may include an indication of why the increased power is not available (e.g., because PTx is already at its maximum input voltage), or may be followed by a subsequent message indicating such information. If the NAK message indicates a reason for not being able to provide increased power other than already being at its maximum input voltage, the receiver may optionally engage in other compensation or negotiation with PTx to attempt to increase the received power (block 457), after which control returns to block 451. Such other compensation or negotiation is beyond the scope of this application and therefore will not be discussed in detail.

[0052] If a NAK message is received (block 453) and the reason for the NAK is that PTx has reached its maximum input voltage Vin (block 454), the receiver controller may decrease the receiver-side series tuning capacitance Crx to increase the gain and therefore the received power (block 456). Before doing so, the receiver controller may optionally decrease its power level to prevent overvoltage (block 455). This is similar to the transmitter-side process described above. In certain operating regimes, for example at relatively high power levels, changing the series tuning capacitance to increase the gain and therefore the received power may cause an overvoltage event at the receiver side. To mitigate this, the power may be temporarily decreased before changing the capacitance. The power level may then be increased after the capacitance change. The change in capacitance on the receiver side can be done in a similar manner as that on the transmitter side, where one or more additional receiver side resonant capacitors Crx2 are optionally decoupled from the receiver coil 122 by opening a switch Qcrx2 to reduce the capacitance, thereby increasing the gain and therefore the power received in block 456. Control can then return to block 451.

[0053] If in block 451 the receiver controller determines that an increase in the wireless power transmitter is not needed or desired, the receiver controller may determine whether it is at a low power level (block 458). If not, control may return to block 451. If instead the receiver controller determines that the receiver is operating at a low power level (block 458), the receiver controller may increase the receiver series tuning capacitance back to the nominal value. The increase in capacitance may be accomplished by closing switch Qcrx2 to couple the resonant capacitor in parallel with capacitor Crx1, thereby increasing the capacitance and decreasing the gain of the system. As with the transmitter side adjustments, the power levels associated with increasing or decreasing the capacitance may be associated with one or more threshold power levels, which may be the same value or may be different values ​​that allow for hysteresis in the transition.

[0054] All of the above operations refer to various voltage levels and thresholds, power levels and thresholds, etc. The teachings herein may be applied to a variety of systems operating at different voltage levels, different power levels, etc. For example, in some embodiments, the input voltage may be controllable, whether by manipulation of a control signal for the DC-DC converter or not, to be in a range between about 16V and 20V. Such a voltage range may, but need not, correspond to a USB-PD power supply providing an input voltage of 20V to such a DC-DC converter. However, operation in other voltage ranges corresponding to other USB-PD voltage levels may also be appropriate. For example, an input voltage range between about 10V-15V or 12V-15V may be used with a 15V USB-PD power supply. Alternatively, if a buck-boost converter is used to provide Vin from a power supply, the upper limit of the voltage range supplied may be above the voltage supplied to such a DC-DC converter. Similarly, with respect to the power threshold, a power threshold of 15W may serve as a boundary between a low power regime and a high power regime. Operating above this threshold may be used to selectively enable or disable features such as input voltage reduction before initiating capacitance changes on either the PTx or PRx side. However, 15W is merely one example of such a threshold, which may be 10W, 12W, 16W, 18W, 20W, 22W, 25W, 28W, 30W, 32W, 35W, 38W, 40W, 45W, 50W, or any other suitable value. If some degree of hysteresis is desired, an additional power threshold may be used to indicate a return to a low power regime. Such a threshold may be 9W, although any value below the high power threshold may be used, such as values ​​of 12W, 10W, 7.5W, 5W, etc. Unless otherwise specified herein or in the appended claims, any of the above values ​​may be used. However, in at least some applications, there may be advantageous reasons to employ a particular threshold.

[0055] Various features and embodiments of dynamic capacitance tuning in wireless power transmission systems have been described above. Such configurations may be used in a variety of applications, but may be particularly advantageous when used with electronic devices such as mobile phones, tablet computers, laptop or notebook computers, and accessories such as wireless headphones, styluses, etc. Furthermore, although a number of specific features and various embodiments have been described, it should be understood that the various features and embodiments may be combined in various permutations in a particular implementation, unless otherwise stated as mutually exclusive. Thus, the various embodiments described above are provided by way of example only and should not be construed as constituting the scope of the present disclosure. Various modifications and variations may be made to the principles and embodiments herein without departing from the scope of the present disclosure and without departing from the scope of the claims.

[0056] The above describes an exemplary embodiment of a wireless power transmission system that can transmit certain information between the PTx and PRx in the system. The present disclosure contemplates that the passing of this information improves the ability of devices to provide wireless power signals to each other in an efficient manner to facilitate battery charging, such as by sharing the power handling capabilities of the devices with each other. Entities implementing the present technology should take care to ensure that, to the extent any sensitive information is used in a particular implementation, well-established privacy policies and / or privacy practices are adhered to. In particular, such entities would be expected to implement and consistently apply privacy practices that are generally recognized as meeting or exceeding industry or government requirements for maintaining user privacy. Implementers should inform users of where personally identifiable information is expected to be transmitted in the wireless power transmission system and allow users to "opt in" or "opt out" of participation. For example, such information may be presented to a user when the user places a device on the power transmitter if the power transmitter is configured to poll for sensitive information from the power receiver.

[0057] Risks can be minimized by limiting data collection and deleting data when it is no longer needed. Alternatively, and when applicable, de-identification of data can be used to protect user privacy. For example, device identifiers can be partially masked to convey device characteristics without uniquely identifying the device. De-identification may be facilitated by removing identifiers when appropriate, controlling the amount or specificity of data stored (e.g., collecting location data at a city level rather than an address level), controlling how data is stored (e.g., aggregating data across users), and / or other methods such as differential privacy. Robust encryption may also be utilized to reduce the likelihood that communications between inductively coupled devices can be spoofed.

Claims

1. A wireless power transmitter, A wireless power transmitting coil; an inverter that receives an input voltage and generates an AC output voltage that drives the wireless power transmit coil; at least one tunable capacitance coupled to the wireless power transmitting coil to form a series tuned circuit with the wireless power transmitting coil; and a control circuit for operating the inverter and the at least one adjustable capacitance to supply wireless power to a wireless power receiver, the control circuit comprising: determining whether the input voltage is at a maximum value, and if so, decreasing the at least one adjustable capacitance to increase gain; or A wireless power transmitter that determines whether the input voltage is at a minimum value, and if so, responds to a power demand from the wireless power receiver by increasing the at least one adjustable capacitance to decrease gain.

2. The wireless power transmitter of claim 1 , wherein the at least one adjustable capacitance comprises one or more capacitors selectively coupleable to the wireless power transmitting coil by one or more switches controlled by the control circuit.

3. 3. The wireless power transmitter of claim 2, wherein the at least one adjustable capacitance includes at least one capacitor coupled to the wireless power transmitting coil and at least two capacitors selectively coupleable to the wireless power transmitting coil by one or more switches controlled by the control circuit.

4. 2. The wireless power transmitter of claim 1 , wherein determining whether the input voltage is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase gain further comprises at least temporarily adjusting the input voltage before decreasing the at least one adjustable capacitance.

5. 5. The wireless power transmitter of claim 4, wherein at least temporarily adjusting the input voltage prior to decreasing the at least one adjustable capacitance is performed by the control circuit in response to an operating power level of the wireless power transmitter.

6. 2. The wireless power transmitter of claim 1 , wherein determining whether the input voltage is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease gain further comprises at least temporarily adjusting the input voltage before increasing the at least one adjustable capacitance.

7. The wireless power transmitter of claim 6 , wherein at least temporarily adjusting the input voltage prior to increasing the at least one adjustable capacitance is responsive to an operating power level of the wireless power transmitter.

8. The wireless power transmitter of claim 1 , wherein the control circuit is configured to increase the at least one adjustable capacitance in response to one or more hard switching events to mitigate the hard switching events.

9. The at least one adjustable capacitance is one or more capacitors selectively coupleable between the inverter output and the wireless power transmitting coil by one or more first switches controlled by the control circuit; 9. The wireless power transmitter of claim 8, further comprising: one or more capacitors selectively coupleable between the inverter output and ground by one or more second switches controlled by the control circuit.

10. the one or more capacitors selectively couplable between the inverter output and the wireless power transmitting coil include at least one capacitor coupled between the inverter output and the wireless power transmitting coil, and at least two capacitors selectively couplable between the inverter output and the wireless power transmitting coil by the one or more first switches; 10. The wireless power transmitter of claim 9, wherein the one or more capacitors selectively coupleable between the inverter output and ground include at least one capacitor coupled between the inverter output and ground and a plurality of capacitors selectively coupleable between the inverter output and ground by the one or more second switches.

11. The wireless power transmitter of claim 8 , wherein the control circuit, in response to a lack of one or more hard switching events, decreases the at least one adjustable capacitance to mitigate the hard switching events.

12. 1. A method of operating a wireless power transmitter having a wireless power transmitting coil, an inverter that receives an input voltage and generates an AC output voltage that drives the wireless power transmitting coil, and at least one adjustable capacitance coupled to the wireless power transmitting coil to form a series tuned circuit with the wireless power transmitting coil, the method being performed by a control circuit of the wireless power transmitter, In response to an increased power demand from a wireless power receiver, determining whether the input voltage is at a maximum value, and if so, decreasing the at least one adjustable capacitance to increase gain; or responsive to a reduced power demand from the wireless power receiver, determining whether the input voltage is at a minimum value, and if so, increasing the at least one adjustable capacitance to reduce gain.

13. 13. The method of claim 12, wherein determining whether the input voltage is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase gain further comprises at least temporarily adjusting the input voltage before decreasing the at least one adjustable capacitance.

14. 13. The method of claim 12, wherein determining whether the input voltage is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease gain further comprises at least temporarily adjusting the input voltage before increasing the at least one adjustable capacitance.

15. The method of claim 12 , further comprising, in response to one or more hard switching events, increasing the at least one tunable capacitance to mitigate the hard switching events.

16. 16. The method of claim 15, further comprising, in response to a lack of one or more hard switching events, decreasing the at least one tunable capacitance to mitigate the hard switching events.

17. A wireless power receiver, A wireless power receiving coil; a rectifier that receives an AC voltage induced in the wireless power receiving coil by a wireless power transmitter and generates a DC output voltage therefrom; at least one tunable capacitance coupled to the wireless power receiving coil to form a series tuned circuit with the wireless power receiving coil; a control circuit for operating the rectifier and the at least one adjustable capacitance to supply power to a load coupled to the DC output voltage of the rectifier, the control circuit comprising: Determining whether a DC input voltage of an inverter of the wireless power transmitter is at a maximum value, and if so, decreasing the at least one adjustable capacitance to increase gain; or determining whether the DC input voltage of the inverter of the wireless power transmitter is at a minimum value, and if so, responding to a power demand from the wireless power receiver by increasing the at least one adjustable capacitance to decrease gain; A wireless power receiver, wherein the DC input voltage is determined by the control circuit in response to one or more messages received from the wireless power transmitter.

18. 20. The wireless power receiver of claim 17, wherein the at least one adjustable capacitance comprises one or more capacitors selectively coupleable to the wireless power receiving coil by one or more switches controlled by the control circuit.

19. 20. The wireless power receiver of claim 18, wherein the at least one adjustable capacitance includes at least one capacitor coupled between the wireless power receiving coil and the rectifier by one or more switches controlled by the control circuit.

20. 20. The wireless power receiver of claim 17, wherein determining whether the DC input voltage of the inverter is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase gain further comprises at least temporarily decreasing the rectifier power before decreasing the at least one adjustable capacitance in response to a rectifier power.

21. 20. The wireless power receiver of claim 17, wherein determining whether the DC input voltage of the inverter is at a minimum value and, if so, increasing the at least one adjustable capacitance to decrease gain further comprises at least temporarily decreasing the rectifier power before increasing the at least one adjustable capacitance in response to a rectifier power.

22. 1. A method of operating a wireless power receiver having a wireless power receiving coil, a rectifier that receives an AC voltage induced in the wireless power receiving coil by a wireless power transmitter and generates a DC output voltage therefrom, and at least one adjustable capacitance that is coupled to the wireless power receiving coil to form a series tuned circuit with the wireless power receiving coil, the method being performed by a control circuit of the wireless power receiver; In response to an increased power demand, determine whether a DC input voltage of an inverter of the wireless power transmitter is at a maximum value, and if so, decrease the at least one tunable capacitance to increase gain; or determining whether the DC input voltage of the inverter of the wireless power transmitter is at a minimum value in response to a reduced power demand, and if so, increasing the at least one tunable capacitance to reduce gain; A method, wherein the DC input voltage is determined by the control circuit in response to one or more messages received from the wireless power transmitter.

23. 23. The method of claim 22, wherein determining whether the DC input voltage of the inverter is at a maximum value and, if so, decreasing the at least one adjustable capacitance to increase gain further comprises at least temporarily decreasing the rectifier power before decreasing the at least one adjustable capacitance in response to a rectifier power.

24. 23. The method of claim 22, wherein determining whether the DC input voltage of the inverter is at a minimum value and, if so, increasing the at least one adjustable capacitance and decreasing a gain further comprises at least temporarily decreasing the rectifier power before increasing the at least one adjustable capacitance in response to a rectifier power.

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