Wireless charging system with start-up negotiation

A wireless power transmission system has a wireless power receiving device that is located on a charging surface of a wireless power transmitting device. The wireless power transmitting device uses measurement circuitry such as coil impedance measurement circuitry or impulse-response circuitry that makes coil inductance measurements to monitor the charging surface for the presence of the wireless power receiving device. In response to detecting that the wireless power receiving device is present on the charging surface, the wireless power transmitting device and the wireless power receiving device establish a wireless communications link. The wireless power transmitting device transmits information on wireless power transmission capabilities of the wireless power transmitting device to the wirelessly power receiving device. The receiving device selects desired settings and transmits these to the transmitting device.

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 to power components in the portable electronic device.

SUMMARY

It can be challenging to regulate the flow of wireless power in a wireless charging system. For example, in a wireless charging system having adjustable operating settings, it can be difficult to determine which settings to use to effectively transmit wireless power to an electronic device.

A wireless power transmission system has a wireless power receiving device that is received on a charging surface of a wireless power transmitting device. The wireless power transmitting device uses measurement circuitry such as coil impedance measurement circuitry or impulse-response circuitry that makes coil inductance measurements to monitor the charging surface for the presence of the wireless power receiving device. In response to detecting that the wireless power receiving device is present on the charging surface, the wireless power transmitting device and the wireless power receiving device establish a wireless communications link.

Using the communications link, the wireless power transmitting device transmits information on wireless power transmission capabilities of the wireless power transmitting device to the wirelessly power receiving device. The transmitted information includes, e.g., minimum and maximum duty cycle settings, wireless power transmission power modulation scheme settings information such as one or more power modulation scheme settings (e.g., a pulse width modulation scheme setting, an amplitude modulation scheme setting, a phase shift modulation scheme setting, etc.), a wireless power transmission sleep timer setting, a wireless power transmission frequency setting, power limits and thresholds, and/or other wireless power transmission settings supported by the transmitting device.

The receiving device uses sensor readings, battery charge state information, and information on which components are active in the receiving device to select desired operating settings. The receiving device transmits the selected settings to the wireless power transmitting device over the wireless communications link.

The information transmitted to the transmitting device by the receiving device includes, e.g., minimum and maximum duty cycle settings, wireless power transmission power modulation scheme settings information such as one or more power modulation scheme settings (e.g., a pulse width modulation scheme setting, an amplitude modulation scheme setting, a phase shift modulation scheme setting, etc.), a wireless power transmission sleep timer setting, a wireless power transmission frequency setting, power limits and thresholds, and/or other wireless power transmission settings for use by the wireless power transmitting device.

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, electronic equipment storage case, 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 in an array of 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.

An illustrative wireless power system (wireless charging system) is shown inFIG. 1. As shown inFIG. 1, wireless power system8includes wireless power transmitting device12and one or more wireless power receiving devices such as wireless power receiving device10. Device12may be a stand-alone device such as a wireless charging mat, may be built into furniture, or may be other wireless charging equipment. Device10is a portable electronic device such as a wristwatch, a cellular telephone, a tablet computer, or other electronic equipment. Illustrative configurations in which device12is a mat or other equipment that forms a wireless charging surface and in which device10is 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 system8, a user places one or more devices10on the charging surface of device12. Power transmitting device12is coupled to a source of alternating-current voltage such as alternating-current power source50(e.g., a wall outlet that supplies line power or other source of mains electricity), has a battery such as battery38for supplying power, and/or is coupled to another source of power. A power converter such as alternating-current-to-direct current (AC-DC) power converter40can 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 circuitry42and other circuitry in device12. During operation, control circuitry42uses wireless power transmitting circuitry34and one or more coil(s)36coupled to circuitry34to transmit alternating-current electromagnetic signals48to device10and thereby convey wireless power to wireless power receiving circuitry46of device10.

Power transmitting circuitry34has switching circuitry (e.g., transistors in an inverter circuit) that are turned on and off based on control signals provided by control circuitry42to create AC signals (drive signals) through coil(s)36. As the AC signals pass through coil(s)36, alternating-current electromagnetic fields (wireless power signals48) are produced that are received by corresponding coil(s)14coupled to wireless power receiving circuitry46in receiving device10. When the alternating-current electromagnetic fields are received by coil14, corresponding alternating-current currents and voltages are induced in coil14. Rectifier circuitry in circuitry46converts received AC signals (received alternating-current currents and voltages associated with wireless power signals) from coil(s)14into DC voltage signals for powering device10. The DC voltages are used in powering components in device10such as display52, touch sensor components and other sensors54(e.g., accelerometers, force sensors, temperature sensors, light sensors, pressure sensors, gas sensors, moisture sensors, magnetic sensors, etc.), wireless communications circuits56for communicating wirelessly with corresponding wireless communications circuitry58in control circuitry42of wireless power transmitting device12and/or other equipment, audio components, and other components (e.g., input-output devices22and/or control circuitry20) and are used in charging an internal battery in device10such as battery18.

Devices12and10include control circuitry42and20. Control circuitry42and20includes 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 circuitry42and20is configured to execute instructions for implementing desired control and communications features in system8. For example, control circuitry42and/or20may 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 circuitry34, processing information from receiving circuitry46, using sensing circuitry to measure coil inductances and other parameters, processing measured inductance values, using information from circuitry34and/or46such as signal measurements on output circuitry in circuitry34and other information from circuitry34and/or46to determine when to start and stop wireless charging operations, adjusting charging parameters such as charging frequencies, minimum and maximum duty cycle settings, coil settings (e.g., which coils are active and weights for active coils) in a multi-coil array, wireless power transfer modulation scheme settings (e.g., one or more desired modulation schemes and power thresholds associated with switching between these scheme(s)), wireless charging sleep interval settings, and wireless power transmission levels, and performing other control functions. Control circuitry42and20may be configured to support wireless communications between devices12and10(e.g., control circuitry20may include wireless communications circuitry such as circuitry56and control circuitry42may include wireless communications circuitry such as circuitry58). Control circuitry42and/or20may 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 system8). 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 circuitry42and/or20. The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, or other processing circuitry.

Device12and/or device10may communicate wirelessly over a wireless communications link established during operation of system8. Devices10and12may, for example, have wireless transceiver circuitry in control circuitry20and42(see, e.g., wireless communications circuitry such as circuitry56and58ofFIG. 1) that allows wireless transmission of signals between devices10and12(e.g., using antennas that are separate from coils36and14to transmit and receive unidirectional or bidirectional wireless signals, using coils36and14to transmit and receive unidirectional or bidirectional wireless signals, etc.).

A circuit diagram of illustrative circuitry for wireless power transfer (wireless power charging) system8is shown inFIG. 2. As shown inFIG. 2, wireless power transmitting circuitry34includes an inverter such as inverter70or other drive circuit that produces alternating-current drive signals such as variable-duty-cycle square waves or other drive signals for implementing a pulse width modulation (PWM) power modulation scheme, variable amplitude square waves or other drive signals for implementing an amplitude modulation (AM) power modulation scheme, or phase-shift modulated drive signals for implementing a phase shift power modulation scheme (as examples). These signals are driven through an output circuit such as output circuit71that includes coil(s)36and capacitor(s)72to produce wireless power signals that are transmitted wirelessly to device10.

Coil(s)36are electromagnetically coupled with coil(s)14. A single coil36and single corresponding coil14are shown in the example ofFIG. 2. In general, device12may have any suitable number of coils (1-100, more than 5, more than 10, fewer than 40, fewer than 30, 5-25, etc.) and device10may have any suitable number of coils. Switching circuitry (sometimes referred to as multiplexer circuitry) that is controlled by control circuitry42can be located before and/or after each coil (e.g., before and/or after each coil36and/or before and/or after the other components of output circuit71in device12to couple the inverter of output circuit71to the array) and can be used to switch desired sets of one or more coils (e.g., coils36and output circuits71in device12) into or out of use. For example, if it is determined that device10is located in a position that overlaps a particular coil36in device12, the coil36overlapping device10may be activated during wireless power transmission operations while other coils36(e.g., coils not overlapped by device10in this example) are turned off.

Control circuitry42and control circuitry20contain wireless transceiver circuits (e.g., circuits such as wireless communication circuitry56and58ofFIG. 1) for supporting wireless data transmission between devices12and10. In device10, control circuitry20(e.g., communications circuitry56) can use path91and coil14to transmit data to device12. In device12, paths such as path74may be used to supply incoming data signals that have been received from device10using coil36to demodulating (receiver) circuitry in communications circuitry58of control circuitry42. If desired, path74may be used in transmitting wireless data to device10with coil36that is received by receiver circuitry in circuitry56of circuitry20using coil14and path91. Configurations in which circuitry56of circuitry20and circuitry58of circuitry42have antennas that are separate from coils36and14may also be used for supporting unidirectional and/or bidirectional wireless communications between devices12and10, if desired.

During wireless power transmission operations, transistors (switches) in inverter70are controlled using AC control signals from control circuitry42. Control circuitry42uses control path76to supply control signals to the gates of the transistors in inverter70. The duty cycle and/or other attributes of these control signals and therefore the corresponding characteristics of the drive signals applied by inverter70to coil36and the corresponding wireless power signals produced by coil36can be adjusted dynamically. Using switching circuitry, control circuitry42selects which coil or coils to supply with drive signals. Using duty cycle adjustments and/or other adjustments (e.g., drive frequency adjustments, amplitude adjustments, phase shift modulation scheme adjustments, etc.), control circuitry42can adjust the strength of the drive signals applied to each coil. A single selected coil may be used in transmitting power wirelessly from device12to device10or multiple coils36may be used in transmitting power. One or more devices10may receive wireless power and each of these devices may have one or more wireless power receiving coils that receive power from one or more corresponding wireless power transmitting coils.

Wireless power receiving device10has wireless power receiving circuitry46. Circuitry46includes rectifier circuitry such as rectifier80(e.g., a synchronous rectifier controlled by signals from control circuitry20) that converts received alternating-current signals from coil14(e.g., wireless power signals received by coil14) into direct-current (DC) power signals for powering circuitry in device10such as load100. Load circuitry such as load100may include battery18, a power circuit such as a battery charging integrated circuit or other power management integrated circuit(s) that receives power from rectifier circuitry80and regulates the flow of this power to battery18, and/or other input-output devices22. Load circuitry100may contain a display, a touch sensor that overlaps the display, one or more touch sensors that are separate from the display, temperature sensors, accelerometers, pressure sensors, force sensors, compasses and gyroscopes, light-based proximity sensors and other proximity sensors, magnetic sensors, and/or other sensors, buttons, a keyboard, audio components such as speakers and microphones, integrated circuits for implementing control circuitry and communications circuitry (e.g., wireless communications circuitry), and/or other components. One or more capacitors C2are used to couple coil14in input circuit90of device10to input terminals for rectifier circuitry80. Rectifier circuitry80produces corresponding output power at output terminals that are coupled to load100. If desired, load100may include sensor circuitry (e.g., current and voltage sensors) for monitoring the flow of power to load100from rectifier80.

The properties (e.g., impedance) of each wireless power transmitting coil36in device12can be affected (e.g., increased) by the presence of overlapping coil(s)14and associated magnetic material (e.g., ferrite core material, etc.) in device10. For example, the inductance L of one or more coils36can increase when device10is present in a position on the charging surface that overlaps those coils. The location(s) of coil(s)14can therefore be determined by making inductance measurements or other signal measurements on each of coils36and processing these measurements (e.g., using interpolation techniques, etc.).

During wireless power transmission operations, transistors in inverter70are driven by AC control signals from control circuitry42. Control circuitry42uses measurement circuitry102to make measurements on coils36(e.g., to monitor the charging surface of device12for the presence of objects such as device10and/or incompatible foreign objects). Measurement circuitry102may be coupled to node N in output circuit71using path104. Measurement circuitry102includes oscillatory circuitry that applies alternating-current probe signals while measuring corresponding signals on node N (e.g., to measure coil impedance and/or changes in coil impedance as the probe signal frequency is maintained at one or more fixed frequencies and/or is swept between first and second frequencies). If desired, measurement circuitry102can include impulse response circuitry. For impulse response measurements, control circuitry42uses inverter70to apply square wave impulse pulses or other impulses to each coil36while using impulse response measurement circuitry in circuitry102to make measurements on output circuit71(e.g., measurements on the inductance L of coil36, measurements of quality factor Q, etc.).

Each coil36in device12(e.g., a coil such as coil36ofFIG. 2that has been selected by control circuitry42using multiplexing circuitry in wireless transmitter circuitry34) has an inductance L. One or more capacitors in output circuit71such as capacitor72exhibit a capacitance C1that is coupled in series with inductance L in output circuit71. When supplied with alternating-current drive signals from inverter70, the output circuit formed from coil36and capacitor72will produce alternating-current electromagnetic fields that are received by coil(s)14in device10. The inductance L of each coil36is influenced by magnetic coupling with external objects, so measurements of inductance L for each coil36in device12can reveal information on device(s)10on the charging surface of device12.

During impulse response measurements, circuitry42uses impulse response measurement circuitry102(sometimes referred to as inductance measurement circuitry and/or Q factor measurement circuitry) to perform measurements of inductance L and quality factor Q. Impedance measurements and other measurements with circuitry102may be initiated in response to detection of an external object on device12using a foreign object detection sensor (e.g., a sensor using coils36and/or other coils, a sensor using light-based sensing, capacitive based sensing, or other sensing techniques, etc.). Impedance measurements and other measurements with circuitry102may also be initiated in response to manual input, based on wirelessly received commands, etc. During the measurements, control circuitry42directs inverter70to supply one or more excitation pulses (impulses) to each coil36, so that the inductance L and capacitance C1of the capacitor72in the output circuit71that includes that coil36form a resonant circuit. The impulses may be, for example, square wave pulses of 1 μs in duration. Longer or shorter pulses and/or pulses of other shapes may be applied, if desired. The resonant circuit resonates at a frequency near to the normal wireless charging frequency of coil36(e.g., about 120 kHz, about 240 kHz, 100-500 kHz, 50-250 kHz, or other suitable wireless charging frequency) or may resonate at other frequencies.

The impulse response (e.g., the voltage V(N) at node N of circuit71) to the applied pulse(s) is as shown inFIG. 3. The frequency of the impulse response signal ofFIG. 3is proportional to 1/sqrt(LC1), so L can be obtained from the known value of C1and the measured frequency of the impulse response signal. Q may be derived from L and the measured decay of the impulse response signal. As shown inFIG. 3, if signal V(N) decays slowly, Q is high (e.g., HQ) and if signal V(N) decays more rapidly, Q is low (e.g., SQ). Measurement of the decay envelope of V(N) and frequency of V(N) of the impulse response signal ofFIG. 3with circuitry102will therefore allow control circuitry42to determine Q and L.

FIG. 4shows how wireless power transmitting circuitry34includes switching circuitry110. Signals from inverter circuitry70are applied to switching circuitry110at input112. Switching circuitry110forms part of wireless power transmitting circuitry34(sometimes referred to as inverter circuitry). Control signals applied to control input116by control circuitry42direct switching circuitry110to route the signals from input112to a selected one of coils36in an array of coils36in device12. Wireless power receiving circuitry46of device10includes one or more coils14. In configurations for device10that include multiple coils14, coils14are coupled to switching circuitry120. Control circuitry20applies control signals to control input122that direct switching circuitry120to route signals from a selected one of coils14to rectifier80via output terminals124.

With one illustrative configuration for wireless transmitting device12, wireless transmitting device12is a wireless charging mat or other wireless power transmitting equipment that has an array of coils36that supply wireless power over a wireless charging surface (e.g., coils36are arranged in a two-dimensional array that lie in a planar housing such as a housing associated with a wireless charging mat. In this type of configuration, coils36of device12are covered by a planar dielectric structure such as a plastic member or other structure forming a charging surface. The lateral dimensions (X and Y dimensions in an arrangement in which the coils lie in an X-Y plane) of the array of coils36in device36may 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. Coils36may overlap on the charging surface or may be arranged on the charging surface in a non-overlapping configuration. Coils36can be placed in a rectangular array having rows and columns and/or may be tiled using a hexagonal tile pattern, a pattern with square tiles, or other pattern.

System8can support one or more wireless power modulation schemes. Illustrative output circuitry (see, e.g., output circuitry71ofFIG. 2) for device12to support pulse-width modulation (PWM) and amplitude modulation (AM) power modulation schemes is shown inFIG. 5. The output circuitry ofFIG. 5includes inverter70. Inverter70has transistors TI1and TI2that supply alternating-current drive signals such as the square wave pulses ofFIG. 6onto coil36and capacitor72. As shown inFIG. 6, in PWM modulation schemes, control circuitry42adjusts the control signals supplied to the gates of transistors TI1and TI2in inverter70to vary the duty cycle (pulse width) of the control signals (e.g., to duty cycle T1/T2in a high duty cycle scenario or to duty cycle T3/T2in a low duty cycle scenario). In amplitude modulation schemes, control circuitry42adjust the magnitude of supply voltage Vsup to inverter70, thereby adjusting the corresponding magnitude (amplitude) Vm of the drive signals supplied by inverter70to coil36and capacitor72. If desired, system8can support a phase modulation scheme by incorporating output circuitry such as inverter70ofFIG. 7into device12. In this configuration, control circuitry42adjusts switches SW (e.g., power field-effect transistors) to supply a phase-modulated drive signal to coil36and capacitor72, as shown by the illustrative drive signal ofFIG. 8. Control circuitry42adjust the magnitude of time periods T4and T5to control the amount of power transfer to device10from device12. Phase-modulated power transfer schemes produce fewer signal harmonics during power transfer operations but are generally less efficient than PWM schemes (e.g., at lower power transfer levels). Output circuitry of the type shown inFIGS. 5 and 7and/or other output circuitry controlled by control circuitry42is included in device12so that device12supports multiple different modulation schemes (e.g., PWM, AM, phase modulation, etc.).

A user may have multiple devices10each of which has different charging requirements. For example, some devices may have batteries that are fully charged and other devices may have depleted batteries. Some devices may have large maximum power transfer capabilities and other devices may have only modest power transfer capabilities. Sensitive devices may be operating in some devices (e.g., wireless communications circuitry that is sensitive to radio-frequency interference, sensitive components such as a touch sensor in a display, display driver circuitry in a display, etc.) while other devices may be sleeping or may not contain any currently operating sensitive devices. Due to these various operating conditions, system8negotiates optimum operating settings for device12and/or device10(e.g., during set-up when device10is first receiving power and/or at other times during the operation of system8). Wireless power transfer settings information is determined by device12using measurement circuitry102(e.g., to detect device10, to measure coil inductance L, etc.) and/or using wireless communications circuitry58to communicate wirelessly with wireless communications circuitry56(e.g., so that wireless power transmitting device12can provide wireless power receiving device10with a list of available wireless power transmission capabilities for the transmitting device and so that wireless power receiving device10can, after analyzing these capabilities and information on the current operating environment of device10, provide device12with corresponding selected power transmission settings).

Conditions that affect optimum power transmission settings include the current operating temperature for device10, battery charge level, and sensitive component operating states (e.g., whether a touch screen display, wireless communications circuit, or other component that is sensitive to radio-frequency interference is currently operating). Adjustable wireless power transmission settings that may be adjusted in device12include the frequency of the drive signals applied to coil36by inverter70, duty cycle settings such as the minimum and maximum duty cycle associated with the drive signals, drive signal amplitude, modulation scheme (e.g., PWM, AM, or phase shift), maximum transmitted power, sleep timer period (e.g., a wireless power transmission sleep timer setting that determines a period of time after which device12awakes from sleep to restart wireless power transmission operations with device10, sometimes referred to as a restart interval or wireless power transmission sleep timer interval), and other settings associated with the transmission of wireless power in system8. Device12can advertise its capabilities to device10(e.g., by transmitting information on wireless power transmission capabilities for device12to device10) and device10can analyze its current operating conditions (temperature, list of active components, battery charge level, etc.) to select from among these capabilities (e.g., to select an optimum charging frequency, modulating scheme, duty cycle settings, maximum transmitted power level, etc.). Device10can then transmit these selected settings to device10to use in transmitting wireless power to device10.

Consider, as an example, a scenario in which device10is a cellular telephone with an active sensitive component such as a touch screen display. The touch screen display (in this example) is sensitive to interference from 140 kHz noise. When device10asks device12to advertise its power transmission capabilities, device12informs device10that its only available wireless power transmission frequency is 140 kHz. Because this is the only available wireless power transmission frequency, device10accepts this wireless power transmission frequency (e.g., device10informs device12to proceed with wireless power transmission operations at 140 kHz), but also directs device12to limit transmitted power to less than 3 W (e.g., device10provides device12with a selected maximum transmit power setting), which is lower than the cellular telephone's power receiving capability (e.g., of 10 W). Because power transmission is restricted in this way, wireless interference from device12will be maintained at acceptable levels and the touch screen display of device12will not be adversely affected during wireless power transmission operations.

If, on the other hand, device10is a wristwatch device with a touch screen display that is currently not active, device10can instruct device12to proceed to transmit at the maximum power reception capability of device10(e.g., 5 W).

Anther possible scenario involves an arrangement in which device12supports wireless power transmission at a range of frequencies (e.g., at least two frequencies). In this arrangement, device12informs device10that frequencies from 100-200 kHz are available and device10choses from these frequencies based on information such as information on which (if any) sensitive components in device10are operating. As an example, a receiving device such as a cellular telephone with an active sensitive device such as a touch screen display or wireless communication circuit that is sensitive to interference at 120 kHz (whether directly at this frequency or because this transmitted frequency is associated with interfering harmonic frequencies), may direct device12to transmit wireless power using a frequency of 128 kHz (which is different than 120 kHz) at a maximum power transmission level of 5 W (which is somewhat reduced from the maximum wireless power reception capability of device10of 10 W).

Duty cycle settings can likewise be established to enhance wireless power transfer performance. Large duty cycle values may be associated with potentially high amounts of transmitted power. If device10is a device with low power reception capabilities, device10can direct device12to use a maximum duty cycle setting of 30% (as an example) to prevent scenarios in which too much power is transmitted. If device10is in need of power to operate (e.g., because device10has a fully depleted battery), device10can instruct device12to use a minimum duty cycle setting of 5% (as an example) to ensure that sufficient power is wirelessly transmitted from device12to device10to allow device10to operate its components while the battery in device10is being replenished.

Device12operates in a normal (wake) mode in which wireless power is being transmitted from device12to device10and, when power is not being wirelessly transmitted (e.g., because device10contains a battery that is fully charged), one or more coils36can enter a sleep mode. In the sleep mode, power consumption is reduced, because operations such as wireless power transmission operations and coil measurement operations with measurement circuit102are temporarily halted (inverter70does not supply drive signals to coil36). A sleep timer is active during sleep mode. The sleep timer runs to a sleep timer interval (e.g., 30 seconds or other sleep time period, sometime referred to as a reset timer setting or sleep timer setting). When the sleep timer expires (e.g., when the sleep time setting is reached by a sleep timer implemented with control circuitry42), device12(e.g., one or more coils36) wakes up from sleep mode and is again available to wirelessly communicate with device10and wirelessly transmit power to device10.

The value of the sleep timer setting can be adjusted (e.g., to a value of 1 ms to 10 minutes, more than 1 ms, more than 1 s, more than 10 s, more than 100 s, more than 1 minute, more than 10 minutes, less than 10 minutes, less than 1 minute, 1-10 minutes, less than 10 s, 10-1000 s, less than 1 s, etc.). Device10can select an appropriate sleep time based on its status when charging is complete (e.g., based on its battery capacity, battery charge level, bias current level, operating temperature, etc.). If, for example, device10is a device with a relatively small battery, device10may direct device12to set the sleep timer to 1 minute. With this setting, after the battery in device10is charged, device12wakes up every 1 minute to check with device10(e.g., over a wireless communications link between device10and device12) to check with device10whether more power is needed by device10. If more power is needed, device12wirelessly transmits power to device10. If more power is not needed, device12returns to sleep. If, as another example, device10is a device with a relatively large battery, device10may direct device12to set the sleep timer of device10a longer time period (e.g., 5 minutes). Because the battery in device10(in this example) is larger, the battery can sustain a longer period of time without being refreshed by power transmission from device12.

In this way, if a user places device10onto device12for an extended period of time relative to the amount needed to fully charge device10(e.g., device10is left on device12for days), device12can sleep after fully charging device10, and periodically awake to see whether the battery level of device10requires further charging in an efficient manner.

As described in connection withFIGS. 5-8, system8may support multiple different power transmission modulation schemes. During set-up operations in which device10and device12are communicating over a wireless communications link or at other suitable times, device12informs device10of the modulation schemes supported by device12. Device10selects appropriate modulation scheme(s) based on the available schemes and based on current operating conditions for device10(operating temperature measured with a temperature sensor, battery charge level, information on which components in device10are currently active, etc.). As an example, if device12informs device10that device12only supports a PWM power transfer modulation scheme, device10can direct device12to use this scheme in wirelessly transferring power to device10. If, as another example, device12informs device10that device12supports both AM and PWM schemes and device10has a partially charged battery, device10can provide device12with wireless power transmission modulation scheme settings information (e.g., one or more modulation schemes and one or more associated power threshold settings) that directs device12to use an AM power transfer modulation scheme to help rapidly charge the battery. In directing device12to use the AM scheme, device10can inform device12to use the AM scheme so long as the power consumed by load100is greater than a threshold amount (e.g., 3 W) and to drop back to PWM for enhanced power transfer efficiency once the power consumed by load100is less than 3 W. By providing device12with power modulation scheme settings such as these or other suitable power modulation scheme settings information, device10can configure system8for optimum power transfer (e.g., based on sensor data, battery charge level, information on currently active components, based on the capabilities of device12, etc.).

Another example related to adjustable power transfer settings involves temperature measurements with a temperature sensor in components100of device10. If operating temperature is measured to be low, device10can direct device12to provide device10with wireless power using a PWM scheme (as an example). Phase-modulation schemes may generate fewer signal harmonics and fewer eddy currents in conductive structures in device10that can raise the temperature of device10. Accordingly, if operating temperature of device10is high, device10can direct device12to supply wireless power using a phase-shifted wireless power transfer modulation scheme. Phase-shifted modulation can also be favored in situations in which sensitive components are operating device10.

A flow chart of illustrative operations involved in using system8is shown inFIG. 9. Device12may use measurement circuitry102and/or other detection circuitry to monitor for the presence of devices10that can receive wireless power. If a user places device10on the charging surface of device12, device12can detect device10(block140). Device12may, as an example, detect a change in the impedance of one or more of coils36, may detect an inductance on one or more of coils36that is elevated relative to adjacent coils36using an impulse-response measurement circuit, or may otherwise sense that device10is present on device12. In response to detecting the presence of a device that appears to be compatible with wireless charging, device12can begin transmitting wireless power to device10. During these power transmission operations, device12can use default power transmission settings (e.g., relatively low power settings) to help power device10sufficiently for device10to use its wireless communications circuitry in the event that device10contains a depleted battery. Device12and device10can then establish a wireless communications link using circuitry56and58(FIG. 1). If desired, device12can attempt to establish a wireless communications link with device10before transmitting power to device10.

During the operations of block142, device10may, if desired, identify itself to device12(e.g., with a serial number, model number, information on operating limits, etc.). Device10can also provide device12with a request that asks device12to supply device10with a list of its capabilities.

During the operations of block144, device12responds to the request of block142that asks device12to transmit information on the wireless power transfer capabilities of device12to device10. As an example, device12can transmit information to device10that informs device10of the supported duty cycle range of device10or other supported duty cycle settings, the supported range of wireless power transfer frequencies (for the drive signal from inverter70), the supported wireless power transfer modulation schemes (e.g., PWM, AM, phase-shifted, and/or other wireless power transfer modulation scheme settings), the supported power transmission range (e.g., minimum power level and/or maximum power level), and/or other wireless power transmission capabilities of device12.

During the operations of block146, device10processes information from sensors in load100(e.g., temperature information from a temperature sensor, and/or other sensor information), information on which components in device10are operating (e.g., whether sensitive components such as a touch insensitive or touch sensitive display, touch sensor (e.g., a stand-alone touch sensor or a touch sensor in a touch sensitive display), wireless communications circuitry, or other components in device10that are potentially sensitive to disruption by radio-frequency signals generated during wireless power transmission, information on the current charge level of the battery in device10and/or other information on the current operating environment of device10and processes information from device12on the wireless power transmission capabilities of device12to determine appropriate settings for use in wireless power transfer operations. Device10may, as an example, determine desired settings based on potentially competing criteria such as criteria related to minimized interference, reduced charging time, maximized safety (e.g., reduced likelihood of circuit degradation with reduced power transmission levels), enhanced power efficiency, minimized signal harmonics (e.g., when using phase-shift modulation instead of PWM to help reduce eddy currents that might heat device10), minimized user wait time, enhanced user expectations, and/or other criteria. After determining settings to use for wireless power transfer operations, device10transmits instructions to device12that contain the appropriate wireless power transfer settings information. The settings may include minimum and/or maximum duty cycle settings, frequency settings, a sleep timer setting, minimum and/or maximum power transfer level settings, modulation scheme settings (including, if desired, associated power transfer level thresholds associated with different modulation schemes) and/or other settings. The instructions direct device12to use these wireless power transfer settings in transferring power wirelessly to device10.

During the operations of block148, device12transfers power wirelessly to device10using the settings information received from device10at block148. When device10is fully charged, device10can wirelessly transmit information to device12that directs device12to stop wireless power transfer operations and to enter a low-power sleep mode. In response, device12sleeps for an amount of time that is specified by a sleep timer setting (e.g., a sleep interval of 1 minute, 5 minutes, more than 5 minutes, less than 5 minutes, etc.) to conserve power (block150). The sleep timer setting may be established using a default setting and/or a setting received from device10(e.g., at step146). When the sleep timer expires (e.g., when the sleep time has reached the sleep timer setting), device12awakes from its sleep state and transmits a request to device10wirelessly that asks device10whether more power is needed to recharge the battery in device10and/or to power components in device10(block152). If no more power is needed by device10, device12can return to the sleep state and, as indicated by line154, control can loop back to block150. If, additional power is needed, processing can loop back to block142, as indicated by line156.

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.