I 1111111111111111 11111 111111111111111 111111111111111 IIIII IIIIII IIII IIII IIII
`US009509168B2
`
`c12) United States Patent
`Ye et al.
`
`(IO) Patent No.:
`(45) Date of Patent:
`
`US 9,509,168 B2
`Nov. 29, 2016
`
`(54) WIRELESS POWER TRANSMITTERS WITH
`WIDE INPUT VOLTAGE RANGE AND
`METHODS OF THEIR OPERATION
`
`(71) Applicant: Freescale Semiconductor, Inc., Austin,
`TX (US)
`
`(72)
`
`Inventors: Wanfu Ye, Shanghai (CN); Xiang Gao,
`Shanghai (CN); Chongli Wu, Queen
`Creek, AZ (US)
`
`7,639,514 B2
`7,855,529 B2
`7,953,369 B2
`8,116,683 B2
`8,129,864 B2
`8,188,619 B2
`8,290,463 B2
`8,294,418 B2
`8,300,440 B2
`8,301,077 B2
`2002/0008981 Al*
`
`12/2009 Baarman
`12/2010 Liu
`5/2011 Baarman
`2/2012 Baarman
`3/2012 Baarman et al.
`5/2012 Azancot et al.
`10/2012 Liu et al.
`10/2012 Hui et al.
`10/2012 Ho et al.
`10/2012 Xueetal.
`1/2002 Jain .
`
`(73) Assignee: FREESCALE SEMICONDUCTOR,
`INC., Austin, TX (US)
`
`2010/0046259 Al
`
`2/2010 Ho et al.
`(Continued)
`
`H02M 7/5387
`363/132
`
`( *) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 232 days.
`
`(21) Appl. No.: 14/082,774
`
`(22) Filed:
`
`Nov. 18, 2013
`
`(65)
`
`Prior Publication Data
`
`US 2015/0061577 Al Mar. 5, 2015
`
`(30)
`
`Foreign Application Priority Data
`
`Sep. 4, 2013
`
`(CN) .......................... 2013 1 0526862
`
`(51)
`
`(2006.01)
`(2016.01)
`
`Int. Cl.
`H02J 7100
`H02J 7102
`(52) U.S. Cl.
`CPC ...................................... H02J 71025 (2013.01)
`( 58) Field of Classification Search
`USPC .................................................. 320/108, 162
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`
`1/2010
`2146414 Al
`2302756 Al
`3/2011
`(Continued)
`
`Primary Examiner - Brian Ngo
`
`(57)
`
`ABSTRACT
`
`The embodiments described herein provide a power trans(cid:173)
`mitter for wireless charging of an electronic device and
`methods of its operation. The power transmitter uses an
`inverter configured to generate a square wave from a poten(cid:173)
`tially wide ranging DC input voltage. The inverter is con(cid:173)
`figured to generate the square wave with a duty cycle that
`results in a desired equivalent voltage output, effectively
`independent of the DC input voltage that is provided. Thus,
`by generating a square wave with a selectable duty cycle the
`inverter provides the ability to facilitate wireless power
`transfer with a wide range of DC input voltages. Further(cid:173)
`more, in some embodiments the power transmitter may
`provide improved power transfer efficiency using a quasi(cid:173)
`resonant phase shift control strategy with adjustable dead
`time and a matching network that is dynamically selectable
`to more effectively couple with the transmitter coil combi(cid:173)
`nation being used to transmit power to the electronic device.
`
`6,160,388 A * 12/2000 Skelton .
`
`7,212,414 B2
`
`5/2007 Baarman
`
`H02M 3/1588
`323/282
`
`20 Claims, 6 Drawing Sheets
`
`216
`
`CONTROLLER - - - - - - - - -~
`
`212
`
`204
`
`VARIABLE DC VOLTAGE
`INPUT
`
`INVERTER
`
`MATCHING
`NETWORK
`
`200--"
`
`Ex.1007
`APPLE INC. / Page 1 of 16
`
`

`

`US 9,509,168 B2
`Page 2
`
`2013/0039099 Al *
`
`2013/0099734 Al *
`
`2013/0119773 Al *
`
`2013/0154384 Al*
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`2013/0187598 Al*
`
`2015/0208492 Al *
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`(56)
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`2010/0171461 Al
`2011/0025132 Al *
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`7/2010 Baarman et al.
`2/2011 Sato .
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`307/104
`
`H02J 5/005
`307/104
`
`H02M 3/3376
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`315/250
`H02J 5/005
`307/31
`
`2/2013 Wu
`
`4/2013 Lee .
`
`H02M 7/53871
`363/40
`H02J 7/007
`320/108
`H02J 5/005
`307/104
`6/2013 Nakamura .............. H0lF 38/14
`307/104
`H02J 7/0042
`320/108
`H05B 41/2985
`315/247
`
`5/2013 Davis.
`
`7/2013 Park.
`
`7/2015 Zhu.
`
`FOREIGN PATENT DOCUMENTS
`
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`
`2010020181 Al
`2010020182 Al
`2011036545 Al
`2011036546 Al
`2011042778 Al
`2011067635 Al
`2013013564 Al
`
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`1/2013
`
`2013/0017798 Al
`
`1/2013 Liu et al.
`
`* cited by examiner
`
`Ex.1007
`APPLE INC. / Page 2 of 16
`
`

`

`U.S. Patent
`
`Nov. 29, 2016
`
`Sheet 1 of 6
`
`US 9,509,168 B2
`
`co
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`Ex.1007
`APPLE INC. / Page 3 of 16
`
`

`

`U.S. Patent
`
`Nov. 29, 2016
`
`Sheet 2 of 6
`
`US 9,509,168 B2
`
`<.O
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`Ex.1007
`APPLE INC. / Page 4 of 16
`
`

`

`U.S. Patent
`
`Nov. 29, 2016
`
`Sheet 3 of 6
`
`US 9,509,168 B2
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`Ex.1007
`APPLE INC. / Page 5 of 16
`
`

`

`U.S. Patent
`
`Nov. 29, 2016
`
`Sheet 4 of 6
`
`US 9,509,168 B2
`
`----------------------------------
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`_____________ ...._
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`--- ---------------- _____________ , _____ ...._ _____________ _
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`Ex.1007
`APPLE INC. / Page 6 of 16
`
`

`

`U.S. Patent
`
`Nov. 29, 2016
`
`Sheet 5 of 6
`
`US 9,509,168 B2
`
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`Ex.1007
`APPLE INC. / Page 7 of 16
`
`

`

`VOLTAGE
`
`DETERMINE INPUT r-802
`DETERMINE r
`
`PROXIMATE PRIMARY
`COIL(S) TO RECEIVER
`COIL(S) ON DEVICE
`
`804
`
`MATCHING NETWORK
`
`CONFIGURE 1 806
`GENERATE POWER r-
`
`TRANSFER SIGNAL
`
`808
`
`800__.A
`
`1
`
`FIG. 8
`
`I
`
`ADJUST
`FUNDAMENTAL
`FREQUENCY
`
`r-810
`
`900 _.A
`FIG. 9
`
`INVERT INPUT
`VOLTAGE TO
`GENERATE SQUARE
`WAVE SIGNAL
`
`GENERATE
`SINUSOIDAL-TYPE
`CHARGING SIGNAL
`
`I FROM SQUARE WAVE
`
`SIG~AL
`
`902
`
`904
`
`906
`
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`
`00
`•
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`"'""' 0--,
`00 = N
`
`I
`APPLY TO PRIMARY k
`I COIL COMBINATION
`
`FOR TRANSMISSION
`TO RECEIVER COIL
`
`Ex.1007
`APPLE INC. / Page 8 of 16
`
`

`

`US 9,509,168 B2
`
`1
`WIRELESS POWER TRANSMITTERS WITH
`WIDE INPUT VOLTAGE RANGE AND
`METHODS OF THEIR OPERATION
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application claims priority under 35 U.S.C. §119 to
`China Patent Application No. 201310526862.3, filed Sep. 4,
`2013, which is incorporated herein in its entirety.
`
`TECHNICAL FIELD
`
`Embodiments of the subject matter described herein relate
`generally to electronic devices, and more particularly to
`wireless power charging for electronic devices.
`
`BACKGROUND
`
`Many modem electronic devices are mobile devices that
`use batteries and/or capacitors as power supplies. In many
`such devices there is a need to frequently recharge the power
`supplies. To facilitate ease ofrecharging such devices wire(cid:173)
`less recharging is increasingly being employed. However,
`there remain significant limitations in many wireless charg(cid:173)
`ing systems. For example, many wireless charging systems
`lack the flexibility to work with multiple types of power
`sources. For example, such wireless power systems may be
`unable to function with power sources having significantly
`varying input voltage.
`Furthermore, many such wireless charging systems con(cid:173)
`tinue to suffer from excessively inefficient power transfer. In
`such systems the amount of power consumed to facilitate
`charging of the mobile device will be excessive, and fur(cid:173)
`thermore may not meet present and future regulatory
`requirements.
`These and other limitations continue to impede the wider
`adoption of wireless power charging of mobile devices.
`Thus, there is a continuing need for improved wireless
`power transfer devices and techniques.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Amore complete understanding of the subject matter may
`be derived by referring to the detailed description and claims
`when considered in conjunction with the following figures,
`wherein like reference numbers refer to similar elements
`throughout the figures.
`FIG. 1 is a simplified system block diagram of a power
`transmitter in accordance with an example embodiment;
`FIG. 2 is a detailed functional block diagram of a power
`transmitter in accordance with an example embodiment;
`FIG. 3 is a schematic diagram of an H-bridge inverter in
`accordance with an example embodiment;
`FIG. 4 are graphical diagrams of square wave signals
`having different duty cycles and magnitudes in accordance
`with an example embodiment;
`FIG. 5 is a graphical representation of a transistor switch(cid:173)
`ing technique in accordance with example embodiments;
`FIG. 6 is a schematic view of a primary coil array in
`accordance with an example embodiment;
`FIG. 7 is a schematic view of a matching network in
`accordance with an example embodiment;
`FIGS. 8-9 are method diagrams illustrating methods for
`wireless power transfer in accordance with an example
`embodiment.
`
`2
`DETAILED DESCRIPTION
`
`The following detailed description is merely illustrative in
`nature and is not intended to limit the embodiments of the
`5 subject matter or the application and uses of such embodi(cid:173)
`ments. As used herein, the word "exemplary" means "serv(cid:173)
`ing as an example, instance, or illustration." Any implemen(cid:173)
`tation described herein as exemplary is not necessarily to be
`construed as preferred or advantageous over other imple-
`10 mentations. Furthermore, there is no intention to be bound
`by any expressed or implied theory presented in the preced(cid:173)
`ing technical field, background, or the following detailed
`description.
`The embodiments described herein can provide wireless
`15 power charging with improved flexibility. For example, the
`embodiments described herein can provide wireless power
`charging that operates with a relatively wide range of input
`voltages. As other examples, the embodiments described
`herein can provide improved wireless power transfer effi-
`20 ciency.
`In one embodiment a power transmitter for wireless
`charging of an electronic device is provided. In general, the
`power transmitter uses an inverter configured to generate an
`alternating current (AC) square wave from a potentially
`25 wide ranging direct current (DC) input voltage. In one
`embodiment the inverter is configured to generate the AC
`square wave with a duty cycle that results in a desired
`equivalent voltage output, effectively independent of the DC
`input voltage that is provided. For example, generating the
`30 AC square wave by utilizing a phase shifting technique
`which the control signals between a first complementary pair
`half bridge and a second complementary pair half bridge of
`an H-bridge inverter. Thus, by generating an AC square
`wave with a selectable duty cycle the inverter provides the
`35 ability to facilitate wireless power transfer within a wide
`range of DC input voltages, and thus may provide improved
`flexibility for wireless power transfer to electronic devices.
`Furthermore, in some embodiments the power transmitter
`may provide improved power transfer efficiency using a
`40 matching network that is dynamically selectable to more
`effectively couple with the transmitter coil combination
`being used to transmit power to the electronic device.
`Furthermore, in some embodiments the fundamental fre(cid:173)
`quency of the power transfer signal is controllable to provide
`45 potentially improved power transfer efficiency.
`Turning now to FIG. 1, a power transmitter 100 for
`wireless charging of an electronic device is illustrated sche(cid:173)
`matically. The power transmitter 100 includes an input 101,
`an inverter 102, a matching network 104 and a primary coil
`50 array 106. The input 101 is configured to receive a variable
`DC input voltage, and using the variable DC input voltage
`the power transmitter 100 is configured to wirelessly trans(cid:173)
`mit power to a receiver coil 108 of a nearby electronic
`device. In general, the inverter 102 is configured to receive
`55 a potentially wide range variable DC input voltage and
`generate an AC square-wave signal having a duty cycle
`selected to provide a predetermined equivalent voltage
`appropriate for power transfer. The AC square-wave signal
`is provided to the matching network 104. The matching
`60 network 104 is configured to generate a charging signal from
`the AC square-wave signal and provide the charging signal
`to the primary coil array 106. The primary coil array 106
`includes a plurality of selectable primary coils. These pri(cid:173)
`mary coils are individually selectable such that selected coil
`65 combinations of one or more primary coils can be used to
`transmit a power transfer signal to a receiver coil 108 of the
`electronic device.
`
`Ex.1007
`APPLE INC. / Page 9 of 16
`
`

`

`US 9,509,168 B2
`
`3
`During operation the inverter 102 generates the AC
`square-wave signal with a duty cycle that results in a desired
`equivalent voltage output independent of the DC input
`voltage. Thus, by generating an AC square-wave signal with
`a selectable duty cycle the inverter 102 may facilitate 5
`operation within a relatively wide range of possible DC
`input voltages. For example, the inverter 102 can be con(cid:173)
`figured to provide the desired equivalent voltage output with
`a DC input voltage that can vary between about 5 and about
`20 volts. In other embodiments the DC input voltage can
`vary between about 5 and about 15 volts. Such an embodi(cid:173)
`ment would provide improved flexibility for wireless power
`transfer using a variety of different power sources. For
`example, such an embodiment can provide the flexibility to
`use both Universal Serial Bus (USB) based power sources
`that are at approximately 5 volts, and automotive power
`sources that are commonly between 9 and 14 volts. In still
`other embodiments, the DC input voltage may vary across a
`voltage range having a higher lower boundary and/or a
`higher upper boundary.
`In one embodiment the desired equivalent voltage gener(cid:173)
`ated by the inverter 102 is based on information from the
`electronic device. For example, the electronic device can
`specify the voltage of the power signal transmitted to the
`receiver coil 108 of the electronic device. As will be 25
`described in greater detail below in some embodiments the
`electronic device can specify such information by transmit(cid:173)
`ting a signal from the receiver coil 108 of the device to the
`primary coil array 106 of the power transmitter 100.
`In one embodiment the inverter 102 comprises a single
`stage inverter. A single stage inverter can provide efficient
`power transfer by minimizing power loss. In one specific
`embodiment the inverter 102 utilizes power metal-oxide(cid:173)
`semiconductor field-effect transistors (MOSFETS), but
`other types of transistors could also be used. In such an
`embodiment the inverter 102 can be configured to adjust
`dead time of the power MOS FE TS based on the magnitude
`of the DC input voltage and loading to facilitate low
`switching loss.
`In one specific embodiment the inverter 102 uses a shifted 40
`phase topology to generate the AC square-wave signal with
`the duty cycle selected. Such an embodiment will be dis(cid:173)
`cussed below with reference to FIG. 5. For example, the
`inverter 102 can utilize a phase-shifted H-bridge topology.
`In one embodiment the inverter 102 is configured to 45
`generate the AC square-wave signal at a plurality of different
`frequencies. In such an embodiment the power transmitter
`100 is further configured to determine which of the plurality
`of different frequencies results in efficient power transfer to
`the electronic device based on feedback received from the 50
`electronic device.
`As described above the matching network 104 is config(cid:173)
`ured to generate a charging signal from the AC square-wave
`signal and provide the charging signal to the primary coil
`array 106. In a typical embodiment the matching network
`104 is implemented such that the generated charging signal
`is a sinusoidal-type signal having a fundamental frequency
`of AC square-wave signal. Furthermore in some embodi(cid:173)
`ments the matching network 104 provides improved power
`transfer efficiency by using selective switching to provide
`more effective coupling with the primary coil combination
`used in the primary coil array 106. In one embodiment this
`is accomplished by including a plurality of switched capaci(cid:173)
`tors and an inductor in the matching network 104. Each of
`the plurality of switched capacitors can be selectively
`switched based upon which of the plurality of selectable
`primary coils are selected. In one embodiment each of these
`
`4
`switched capacitors is configured to make the resonant
`frequency of the power transmitter near the fundamental
`frequency of the charging signal when the corresponding
`primary coil combination is active.
`As described above, the primary coil array 106 includes
`a plurality of selectable primary coils, in an embodiment.
`These primary coils can be implemented with any combi(cid:173)
`nation of wire-wound coils, printed circuit board (PCB)
`coils, or hybrid/wire-wound coils. These primary coils are
`10 individually selectable such that a coil combination of one or
`more primary coils in the array 106 can be selected and used
`to transmit a power transfer signal to a receiver coil 108. In
`one specific embodiment each of the plurality of selectable
`primary coils are selectively activated to utilize a coil
`15 combination that is most effective to couple with the receiver
`coil 108 of the electronic device. As will be described in
`greater detail below, the most effective coil combination can
`be selected based on a feedback signal received from the
`electronic device, where the feedback signal provides an
`20 indication of power transfer efficiency. In an alternate
`embodiment, the primary coil array 106 may include only a
`single coil, rather than multiple coils.
`The power transmitter 100 can be implemented with a
`variety of other elements. For example, the power transmit(cid:173)
`ter 100 can be further implemented with an input voltage
`detector configured to determine a magnitude of the DC
`input voltage. In such an embodiment the inverter 102 can
`be configured to select the output duty cycle by using phase
`shift technique to provide the predetermined equivalent
`30 voltage based on the magnitude determined by the input
`voltage detector.
`As another example, the power transmitter 100 can be
`further implemented with a sensing circuit coupled to the
`plurality of selectable primary coils in the primary coil array
`35 106. In such an embodiment the sensing circuit can be
`configured to sense signals received on at least one of the
`plurality of selectable primary coils to facilitate communi(cid:173)
`cation transmitted from the electronic device back to the
`primary coils. The communication messages include, but are
`not limited to, the information of power transfer efficiency
`and energy requested by the electronic device.
`Finally, in some embodiments the power transmitter 100
`can further include a microcontroller. In such an embodi(cid:173)
`ment the microcontroller can be configured to control opera(cid:173)
`tion of the inverter 102, the matching network 104 and/or the
`plurality of selectable primary coils 106. Furthermore the
`microcontroller can be used to control other elements, such
`the input voltage detector and sensing circuit described
`above.
`In one specific embodiment the microcontroller is coupled
`to an input voltage detector, a sensing circuit, the inverter
`102, the matching network 104, and the coil array 106 and
`may be configured to control the inverter 102 to generate the
`AC square-wave signal with a duty cycle selected based on
`55 the determined magnitude of the DC input voltage such that
`the AC square-wave signal provides a predetermined
`equivalent voltage. Furthermore, the microcontroller may be
`configured to control the plurality of selectable coils in the
`coil array 106 to selectively activate a coil combination
`60 effective to couple with the receiver coil 108 on the elec(cid:173)
`tronic device. Furthermore, the microcontroller may be
`configured to selectively couple the plurality of switched
`capacitors in the matching network 104 based on the acti(cid:173)
`vated coil combination. The microcontroller also may be
`65 configured to receive communication from the receiver coil
`108 on the electronic device based on a signal received on
`at least one of the plurality of selectable primary coils.
`
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`5
`Finally, the microcontroller may be configured to control the
`power transferred from transmitter to the receiver coil 108 of
`the electronic device based on the communication message
`(s) received by microcontroller.
`Turning now to FIG. 2, an exemplary embodiment of a 5
`power transmitter 200 for wireless charging of an electronic
`device is illustrated schematically. The power transmitter
`200 includes a differential input 201, an inverter 202, a
`matching network 204, a primary coil array 206, a voltage
`detector 208, an inverter driver 210, a sensing circuit 212, 10
`coil switches 214, and a controller 216. In general, the power
`transmitter 200 is configured to receive a variable DC input
`voltage at the differential input 201 and wirelessly transmit
`power to a receiver coil of a nearby electronic device. In
`general, the inverter 202 is configured to receive a paten- 15
`tially wide range variable DC input voltage and generate an
`AC square-wave signal having a duty cycle selected to
`provide a predetermined equivalent voltage. The matching
`network 204 is configured to generate a charging signal from
`the AC square-wave signal and provide the charging signal 20
`to the primary coil array 206. In this illustrated embodiment
`the AC square wave and charging signal are passed as
`differential signals. The primary coil array 206 includes a
`plurality of selectable primary coils that are individually
`selectable such that a selected coil combination of one or 25
`more primary coils can be used to transmit a power transfer
`signal to a receiver coil of the electronic device.
`The voltage detector 208 is configured to determine the
`magnitude of the variable DC input voltage and provide a
`signal indicating that magnitude to the controller 216. Based
`on the provided magnitude, the controller 216 controls the
`inverter driver 210 to control the operation of the inverter
`202. Specifically, the controller 216 uses the magnitude and
`a sensed primary coil signal from sensing circuit 212 in
`determining a duty cycle for the AC square-wave signal by
`utilizing the phase shift technique. Based on the determined
`duty cycle, the controller 216 controls the inverter 202 (via
`inverter driver 210) to provide a desired equivalent voltage
`in the AC square-wave signal generated by the inverter 202.
`The controller 216 uses the inverter driver 210 to control the
`inverter 202 to generate this AC square-wave signal.
`The coil switches 214 are coupled to the controller 216
`and the primary coil array 206. The controller 216 selec(cid:173)
`tively activates the coil switches 214 to control which
`primary coils in the array 206 are activated for use in
`transmitting power to the electronic device. These coil
`switches 214 can be activated to enable a coil combination
`of one or more primary coils in the array 206. Typically the
`coil combination used would correspond to those coils in the
`array 206 that have the best coupling with the corresponding
`receiver coil on the electronic device, and thus facilitate
`efficient power transfer to the electronic device. In an
`alternate embodiment, the primary coil array 206 may
`include only a single coil, rather than multiple coils, and the
`coil switches 214 may be excluded from the system.
`The sensing circuit 212 is coupled to the plurality of
`selectable primary coils in the primary coil array 206. The
`sensing circuit 212 is configured to sense voltage/current
`levels on the on the primary coil array 206. This can be used
`to sense the current power transfer amount and signals
`transmitted from the electronic device and received by the
`primary coil array 206. Thus, the primary coil array 206 can
`be used to both transmit power to an electronic device for
`recharging, and can also be used to receive communications
`from the electronic device.
`In one embodiment the communication from the elec(cid:173)
`tronic device may be implemented using a technique,
`
`6
`referred to as load modulation, that includes changing the
`load of the receiver side for defined periods according to a
`specific standard protocol, such as a protocol defined in a
`Wireless Power Consortium wireless power transfer speci(cid:173)
`fication. In this implementation the load changes result in a
`modulation of the current through and/or voltage across the
`primary coil(s), which modulation can be sensed by the
`sensing circuit 212 and conveyed to the controller 216. The
`controller 216 can use the different timing periods between
`load changes to extract the communication message. In this
`case the communication message may be conveyed using a
`low frequency signal, as compared with the frequency of the
`power transfer signal.
`Such a transmission of information to the power trans(cid:173)
`mitter 200 can be utilized for a variety of purposes. For
`example, the electronic device can transmit information to
`the power transmitter 200, which indicates the amount of
`power that is being received by the electronic device. Such
`information can be used by the controller 216 to select the
`most efficient parameters for power transmission. As one
`example, such information can be used to identify a suitable
`receiver coil to receive the power. As another example, the
`information can be used to determine which of the plurality
`of selectable primary coils in the array 206 should be used
`to transmit power to the electronic device with maximum
`efficiency. As other examples, the information can be used to
`determine the fundamental frequency of the charging signal
`that results in the highest efficiency power transfer. As other
`examples, the information can be used to transmit a power
`30 amount required by receiver. As other examples, the infor(cid:173)
`mation can be used to determine how long the power transfer
`will continue.
`Turning now to FIG. 3, an embodiment of an inverter 302
`is illustrated. Inverter 302 is exemplary of the type of
`35 inverter that can be used in the various embodiments
`described herein, including in the examples illustrated in
`FIGS. 1 and 2 (e.g., inverters 102, 202).
`In general, the inverter 302 includes an input 304, an
`output 306, and four transistors Pl, P2, P3 and P4. In the
`40 illustrated embodiment these transistors are implemented
`with power MOSFETS and are arranged in an H-bridge
`topology. Specifically, transistors Pl and P3 are arranged as
`a first complementary pair and transistors P2 and P4 are
`arranged as a second complementary pair. When transistors
`45 Pl and P4 are on (and transistors P2 and P3 are off), the
`output is driven positive, and when transistors P2 and P3 are
`on (and transistors Pl and P4 are off), the output is driven
`negative. Finally, when transistors Pl and P2 are on (and
`transistors P3 and P4 are off), or transistors P3 and P4 are on
`50 (and transistors Pl and P2 are off), the output is zero. Thus,
`by providing an appropriate DC input at input 304, and
`appropriately controlling the transistors Pl, P2, P3 and P4
`the inverter 302 and outputs an AC square-wave signal at
`output 306. Furthermore, by controlling the timing of the
`55 transistor activation (e.g., by controller 216 and inverter
`driver 210, FIG. 2) the duty cycle of the AC square-wave
`signal can be controlled.
`Turning now to FIG. 4, two graphical representations of
`AC square-wave signals are illustrated. These AC square-
`60 wave signals are exemplary of the type of AC square-wave
`signals that can be generated by the inverter 302. The AC
`square-wave signals have a controllable duty cycle that
`results in a desired equivalent voltage output, effectively
`independent of the DC input voltage that is provided. The
`65 duty cycle of the AC square-wave signal is the ratio of the
`duration of the signal at active state(s) to the total period of
`a signal. In the examples of FIG. 4, these active states
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`5
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`7
`comprise both the high ( +) and low (-) portions of the
`waveforms. Thus, graph 402 illustrates an example where
`the duty cycle of the AC square-wave signal is relatively
`high (i.e., a high ratio), while graph 404 illustrates an
`example where, by comparison, the duty cycle of the AC
`square-wave signal is relatively low (i.e., a low ratio). Graph
`402 thus illustrates an example of the type of AC square(cid:173)
`wave signal that would be generated when the DC input
`voltage was relatively low, while graph 404 illustrates an
`example of the type of AC square-wave signal that would be
`generated where the DC input voltage was relatively high. In
`both examples the difference in duty cycle can be used to
`generate the same desired equivalent voltage output in the
`AC square-wave signal, even though the DC input voltage
`used to generate those signals was different. Thus, control- 15
`ling the duty cycles of the AC square-wave allows different
`DC input voltages to be used while providing the needed
`equivalent voltage at the output nodes for wireless charging.
`Again, such AC square-wave signals as those illustrated
`in graphs 402 and 404 can be generated by switching 20
`transistors Pl and P4 on for the positive portions of the
`waveform (while switching transistors P2 and P3 off),
`switching transistors P2 and P3 on for the negative portions
`of the waveform (while switching Pl and P4 off), and
`switching either transistors Pl and P2 or transistors P3 and 25
`P4 on (and correspondingly switching transistors P3 and P4
`or transistors Pl and P2 off) for the neutral portions of the
`waveform.
`A variety of different techniques can be used to reduce
`power consumption in the inverter 302. In one embodiment 30
`the inverter 302 is configured to adjust the dead time of
`transistors to facilitate low switching loss. Specifically, the
`controller can operate the transistors in the inverter 302 to
`adjust the dead time of the transistors to assure quasi(cid:173)
`resonant soft switching for low switching losses according 35
`to different input voltages and loads. Furthermore, the
`inverter 302 can be operated to use shifted phase topology.
`In general, a shifted phase topology is an implementation of
`50% duty cycle control signal at each transistor pair of a
`full-bridge inverter by phase shifting the switching of one 40
`transistor pair (half-bridge) control signal with respect to the
`other. Such a phase shifted topology can facilitate constant
`frequency pulse-width modulation in conjunction with reso(cid:173)
`nant zero-voltage switching to provide high efficiency at
`high frequencies.
`Turning now to FIG. 5, a graphical representation 500 of
`a transistor switching technique and a graphical representa(cid:173)
`tion 504 of the resulting AC square-wave signals generated
`using an embodiment of a power transmitter ( e.g., power
`transmitter 200, FIG. 2) are illustrated. This illustrated 50
`technique switches the transistors ( e.g., of inverter 102, 202,
`302, FIGS.1-3) to generate a d