Examining Wireless Power Transfer

John Rice

Agenda

3-2 Texas Instruments – 2014/15 Power Supply Design Seminar

•  Introduction 5 min. –  Foundational principles of electromagnetics –  Power transfer - near and far field

•  Existing and Emerging Wireless Power Standards 5 min. –  WPC, PMA, A4WP comparison –  Electromagnetic field safety implications of WPT

•  Theory of Operation 20 min. –  Considering loosely coupled coils –  Modeling resonant power transfer –  Magnetic link efficiency –  Topological analysis with SPICE and FEA

•  Design Considerations 20 min. –  RX to TX communication –  Intelligent voltage positioning and load response –  EMI, efficiency/loss measurement –  Foreign object detection – eddy loss detection –  Single coil, 5 W WPC design example

Notable Dates in Wireless Power Transfer

3-3 Texas Instruments – 2014/15 Power Supply Design Seminar

•  1820: Biot–Savart / André-Marie Ampère / H. Oersted discover and quantify relationship between electric current and magnetic fields

•  1831: Michael Faraday / H. Hertz discover electromagnetic induction

•  1834: Lenz (Lenz‘s law) à N. Callan invents the electrical transformer

•  1864: James Clerk Maxwell synthesizes previous observations and mathematically models electromagnetic radiation

•  1891-1917: Nicola Tesla – enormous contribution to the practical application of resonant power transfer and electromagnetic induction; numerous discoveries and patents

 •  2007: WiTricity research group, led by Professor Marin Soljacic advances magnetic

resonance to wirelessly power a 60 W light bulb with 40% efficiency at 2 m using 60 cm-diameter coils

•  2008/9: A consortium of companies called the Wireless Power Consortium (WPC) announces the evolution of a industry standard for low-power (5 W) inductive charging

0.1 1 10

Wave Impedance104

1x103

100

10

Near Field

Magnetic Field Electric Field

Far Field

Wireless EnergyTransfer

ElectromagenticRadiation

ElectromagneticInduction

ElectrodynamicInduction

ElectrostaticInduction

Microwave/RFPower

Light/LaserPower

MagneticInduction

Magnetic ResonantInduction

ZDC ZLC

Electromagnetic Wave Propagation

Texas Instruments – 2014/15 Power Supply Design Seminar 3-4

E ∝1/r3, H ∝1/r2 E ∝1/r, H ∝1/r

E ∝1/r2, H ∝1/r3

ZO = 377 Ω, Plane Wave

rc ⋅β

•  Field defined by antenna and distance from source

•  Dipole(red) and loop(blue) antennas shown

•  Wave impedance = E/H, converges at λ  >>1  

•  Reactive near field below λ/2π  is non-radiative

Alliance for Wireless Power

3-5 Texas Instruments – 2014/15 Power Supply Design Seminar

Race for a Wireless Charging Standard Safety, Performance, Reliability and Interoperability

Protocols Power Frequency Band

Communication Frequency Band

Range of Coupling

Wireless Power Consortium (WPC) 105-205 kHz Same as power

transfer band 0.4 to 0.7

Powermat (PMA) 277-357 kHz Same as power transfer band 0.6 to 0.8

Alliance for Wireless Power (A4WP) 6.78 MHz 2.4GHz ISM

(ZigBee or BLE) 0.1 to 0.5

BatteryMagnetic Shield

AC MagneticFlux

RX CoilRX Coil

TX CoilTX Coil

Magnetic (Ferrite) Shield

DCAlignment

Magnet

3-6

Safety Considerations Electromagnetic Radiation Effect

Texas Instruments – 2014/15 Power Supply Design Seminar

Frequency Range

E-field (V/m)

H-field (A/m)

B-field (µT)

0.025-­‐0.8  kHz   250/f   4/f   5000/f  

0.15-­‐1  MHz   87   0.73/f   0.92/f  1-­‐10  MHz   87/f^0.5   0.73/f   0.92/f  

3-7 Texas Instruments – 2014/15 Power Supply Design Seminar

Theory of Operation

E • dA =Q∑

ε0

∫

B• dA = 0∫E • dl = −

ddt

B• dAS∫∫

B• dl = µ0Ienc∫ + µ

0ε0

dϕE

dt

µ0= Vacuum _ permeability

ε0= Vacuum _ permittivity

D2

D1

RX

TX

Z

3-8 Texas Instruments – 2014/15 Power Supply Design Seminar

Loosely Coupled Coils Self and Mutual Inductance

V1(t) = R

1i1(t) + L

1

di1(t)

dt+ / −M

di2(t)

dt

V2(t) = R

2i2(t) + L

2

di2(t)

dt+ / −M

di1(t)

dt

Ρ =φ

Ni=µA

l,φ = ΡNi

Vc= N

dφ

dt= N

d(ΡNi)

dt= N2

µA

l

di

dt= L

di

dt

L =Nφ

i,φ1= φ

11+ φ

21

V2= N

2N1Ρ21

di1

dt→ M = N

2N1Ρ21

Physical representaion of flux coupling Electrical representation of flux coupling

V2 (t)V1 (t)i1 (t)

N2N1

21

11R1 I1(t) R2

V2L1 L2

M, k

V1

I2(t)

TXRX

IoutVP

IPRL

RLVS

Ideal Transformer k = 1

Cantilever Transformer Model

Leakage Impedance Cancelation

Non-Ideal Transformer k<<1

Load Reflected to Primary is Propotional to k2

IS

N

N2N1

IP IS

R1k LSLP RL

N:1

LIkg LIkgLm RL’ LmC2

C3C1

RL’

3-9 Texas Instruments – 2014/15 Power Supply Design Seminar

Power Transfer, Wired and Wireless

Wired/ Tightly Coupled

Loosely Coupled WPT

Load Reflected to Primary

RL' = N2 •RL = RL • k2 •LPLS

N = k •LPLS

Pout =VP

2

RL•NSNP

⎡

⎣⎢⎢

⎤

⎦⎥⎥

2

Llkg = (1− k2 )•LP

Lm = k2 •LP

VPVS

=ISIP

=NPNSPout =

V2

RL

T

Frequency (Hz)

89.51k 102.17k 116.63k

Ga

in (

dB

)

10.00

20.00

30.00

40.00

Series Resonant Tank

Parallel Resonant Tank

RL

RL

3-10 Texas Instruments – 2014/15 Power Supply Design Seminar

Considering Resonance

3dB

fr = 1/ 2π LCQ =

frΔf3dB

fr

Δf3dB

XC = 1ωC

XC = 1ωC

I = VZeqp

I = VZeqs

XL = ωL Rω

XL = ωL Rω

3-11 Texas Instruments – 2014/15 Power Supply Design Seminar

Coil Skin and Proximity Losses (Eddy Induced Losses)

Rpac =ωLpQp Rsac =

ωLsQs

R' = k2 i

LpLs

Rs+RL( )

IeIeL-IDEAL

RAC

RDC

RL

H-Field

Current Flow

TX

RX

VS

VS

RP

LP LS

R’

k<<1

Non-Ideal TX/RX Inductor Skin Effect Proximity Effect

3-12 Texas Instruments – 2014/15 Power Supply Design Seminar

Typical WPC TX/RX Coil Q and Skin/Proximity Effect

RX: 40 x 30 mm with shield Litz wire, 2 strands 14 turns, 1 layer Q = 2.3 @ 130 kHz Rac = 515 mΩ @ 130 kHz

TX: 43 mm diameter with shield Litz wire, 105 strand 20 turns, 2 layers Q = 100 @ 130 kHz Rac = 176 mΩ

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0

50

100

150

200

100K 150K 200K 250K 300K

TR1/Ohm

TR2/Q

f/Hz

TR1: Real(Impedance) RX : Real(Impedance)TR2: Q(Impedance) RX : Q(Impedance)

3-13 Texas Instruments – 2014/15 Power Supply Design Seminar

Primary Current vs. Frequency and Coupling Coefficient

ZIN f,k( ) = RP +R k( ) i  QP f,k( )2

1+QP f,k( )2+ j(XLS f,k( )− XCr f( ) +R k( ) i QP(f,k)

1+QP(f,k)2 )

ir(f, k) =VfundamentalZIN(f, k)

2)()()( knRLRSkR +=

VIN

Cr Rp

Cr Rp

RS CS

RS

R

CS

C

RL

RL

Io

Iot

L2Ir

Ir

L1

LS

Lp

Cr Rp

Ir

LS

Lp

n 1

VIN

IDEAL

6

4

2

0

0 5x104 1x10

5 1.5x10

5 2x10

5

Frequency (Hz)

Re

so

na

nt

Cu

rre

nt

(A)

k = 0.3

k = 0.4

k = 0.5

k = 0.6

3-14 Texas Instruments – 2014/15 Power Supply Design Seminar

Coupling Efficiency

Coupling Efficiency in Relationship to Coil Separation (z) and the Ratio of Coil Diameters

Coil Vertical Displacement z/(D), Normalized

Mag

netic

Effi

cien

cy Coil Separation, Normalized

Rat

io o

f Coi

l Dia

met

ers

Q=100

0.01 0.1 1 100.0001

0.001

0.01

0.1

1Drx = DtxDrx = 0.3 DtxDrx = 0.1 DtxDrx = 0.03 DtxDrx = 0.01 Dtx

Magnetic Figure of Merit F(k,Q)

3-15 Texas Instruments – 2014/15 Power Supply Design Seminar

•  Q = geometric mean of coil quality factors =

•  Q influenced strongly by skin

and proximity effect

•  High Q compensates for poor coupling

•  High Q requires greater control bandwidth

Qp ×Qs

30 mm Planar Coils

λ k,Q( ) : = 2

k × Q( )2 × 1+ 1+ (k × Q)2⎡

⎣⎤⎦

0 0.2 0.4 0.6 0.8 1

Qsys=100Qsys=50Qsys=30Qsys=10

Coupling Coefficient, kEf

ficie

ncy

0 10 20 30 400

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1k(2 mm)k(2.5 mm)k(5 mm)k(10 mm)

Center Displacement

Cou

plin

g, k

Vert

ical

Sep

arat

ion

Coil Displacement

Coupling Coefficient and Mutual Inductance from Transfer Gain

3-16 Texas Instruments – 2014/15 Power Supply Design Seminar

k =Lrx

Ltx•Vtx

Vrx=Gain

Lrx

Ltx

Ltx = 25 µH

k(gap = 0 mm) =0.516

LrxLtx

= 0.83, M = 13.6µ

k(gap = 8 mm) =0.208

LrxLtx

= 0.321, M = 5.27µ

Lrx = 10.8 µH M = k • Lrx • Ltx

Typical 5 W coils Connected to a VNA

zgap = 8 mm

zgap = 0 mmf = 125 kHz, Gain = 0.516

f = 125 kHz, Gain = 0.208

1

0.10.20.30.40.50.60.70.8

1.0x105 1.5x105 2.0x105

TR1

f/HzTR1: Mag(Gain) Memory 1 : Mag(Gain)

Intelligent WPT Digital Power, Resonant Battery Charger

3-17 Texas Instruments – 2014/15 Power Supply Design Seminar

•  A transmitter (TX) driving a resonant coupled inductor

•  A receiver (RX) with rectification, load modulation and post regulation

•  A load, commonly a single cell, secondary battery pack

Resonant Circuit Analysis

3-18 Texas Instruments – 2014/15 Power Supply Design Seminar

•  VG1 is a variable frequency AC signal in frequency domain

•  VG1 is a 50% duty cycle, 19 V square wave in the time domain

•  Power regulated by changing the frequency or voltage

 

20 × Log

VOUT

VIN

⎛⎝⎜

⎞⎠⎟= 20 × Log

7.65

19( )dB = − 7.902 dB

Resr_RX 641m Cr_RX 183n+

VG1

Cr 100n Resr_TX 452mVAC

LTX 25 µ LRX 10.8 µ

K = 0.8K

-

+Vcoil_TX

RLOAD 5

COUT 4.7 µ

VOUT 1

T

Frequency (Hz) 70.00 k 167.33 k 400.00 k

Gai

n (d

B)

-24.23

-2.48

19.26

a

Time (s) 300.00 µ 320.00 µ 340.00 µ

VOUT 4.60

4.80

VAC

5.25

VG10.00

19.00

Vcoil_TX -19.43

19.45

VAC[3]: k= 800 m, Q=34.7

f=170kHz, Gain = -7.9 dB

VAC[1]: k = 200 m

Examining Circuit Behavior in SPICE

3-19 Texas Instruments – 2014/15 Power Supply Design Seminar

Time (s)1.70m 1.71m 1.72m 1.73m 1.74m 1.75m 1.76m 1.77m

VOUT

4.00

6.00

Iprim-1.93

1.93

VSW-1.00

30.00

Vcoil_rx-20.00

20.00

Vcoil_tx-30.00

30.00

Vcoil_rx, RMS = 8.25V

Vcoil_tx, RMS = 18.7V

Isec, RMS = 1.2A

-+

-

+-

+

-

+

VgVset

U1

-

+ VCOSqr

GND

VDD

FM PHASEBoot

HGATE

GND LGATE

TPS28225 Rboot 1

Cboot 100n

T2

T1

C110 µ

C3100 µ

L8

R8

VSW K K = 0.55

L7

C62.2 m

OUTLISN

IN

M1

R650

M2

RACp

425 m

RACs

641 mIprimVcTX VcRX

CRx100 n

CRx220 n

LTX

25.4

µ

LRX

10.8

µ

VIN 19

VM1

RL 5VOUT

ISECCOUT4.7 µ

2-D FEA Plot of Magnetic Flux Between TX/RX Coils

3-20 Texas Instruments – 2014/15 Power Supply Design Seminar

•  Receiver side shielding is important

•  Poorly designed shields expose battery and external circuits to magnetic field

•  AC/DC winding losses of TX/RX coils correspond with empirical results = 0.32 W

Ferrite Shield (TX)

Litz Coil (RX)

Ferrite Shield (RX) Aluminum (Battery or Internals)

Litz Coil (TX)

Axisymmetric FEA Evaluated in FEMM

Control

Linear

Controller

Voltage

Regulation / OV

Protection

Control and

Modulation

Synchronous

Rectifier

Receiver

DC/

DC

Driv

er

Control &

Demodulation

+

-

100%

90%

80%

70%

60%

50%

40%

30%

20%

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Eff

icie

nc

y (

%)

Tx Eff. Magnetics Eff. Rx Eff. System Efficiency

Output Power (W)

3-21 Texas Instruments – 2014/15 Power Supply Design Seminar

Quantifying Losses – Typical 5 W Wireless Power Transmitter/Receiver

η =POUT

POUT + PRX + PTX

PTX = PTXcoil + PBridge + Pcontrol + PDC−DC PRX = PRXcoil+ Prectifier+ PIdo + Pcomm

3-22 Texas Instruments – 2014/15 Power Supply Design Seminar

Design Considerations, WPC

•  Feedback communication

•  Loop response

•  Foreign object detection

•  Electromagnetic compatibility

•  System efficiency

3-23 Texas Instruments – 2014/15 Power Supply Design Seminar

WPC 1.1 Compliant 5 W TX Reference Design

GND

PGND

GND

10.0kR19

10.0kR22

10.0kR23

J_CLK

J_DATA

DATA

CLK

GND

Vcc

PMBUS

JTAG

12345678910

J2

0.1µFC10

F

L1

0.1µFC18

0.1µF

0.1µF

C15

GND

76.8kR13

10.0kR14

0.1µFC3

GND

0.02

R18

1.00kR12

GND

PGND

0.1µFC12

10.0kR17

t°NTC1

GND

123456789101112131415 16 17 18 19 20 21 22 2 3 24 25 26 27

DRV

_EN

PWM

_CTR

L

AV

SS

AV

CC

PWM

1/CL

K_O

UT

PWM

2/U

P_D

N

I_SE

NSE

PEA

K_D

ET

V_S

ENSE

FOD

_GA

IN

LED

_GRN

LED

_RED

T_SE

NSE

MO

DE

BUZZ

N/C

JTA

G_C

LK

JTA

G_D

ATA

UA

RT/C

LK_I

N

COM

M1

COM

M2

SDA

SCL

V_C

ORE

DV

SS

DV

CC

LED

FOD

_TH

R28

U1

0.1µFC6

GND

DA

TA

CLK LED

FOD_THR

J_CL

K

J_D

ATA

1000pFC21

GND

C16

0.1µFC17

GNDGND GND

1

2

3

4

5

6789

1011

USB

J1

GNDGND

TANK

TANK

GNDGNDGND

FOD_THR LED

1.00kR3

1.00kR4

Place close to U2

GND

0.1µFC9

GNDPGND

PGND

10.0kR5

10.0kR6

10.0kR7

10.0kR8

10.0kR9

10.0kR10

10.0kR25

69.8kR24

523kR21

0.01µF

C20 1000pFC23

2700pFC22

GreenD2

RedD3

PWM1/CLK_IN1

PWM_CTRL2

EN3

BP34

AGND5

AGND6

DMOUT27

DMOUT18

CLK

_OU

T9

MO

DE

10

DM

IN1

11

DM

IN2

12

AG

ND

13

PVIN

214

PVIN

215

BOO

T216

SW2 17SW2 18SW2 19

PGND 20PGND 21PGND 22

SW1 23SW1 24

BOO

T125

SW1

26PV

IN1

27PV

IN1

28CS

-29

CS+

30CS

O31

PWM

2/U

P_D

N32

PWRP

AD

33

U2

Vcc

TP8

TP7

PGND

499R20

499R1

GND

TP9

TP11

TP2

TP3

TP14

TP15

TP4

TP5

0.47µFC8

TP12

TP10

0R15

0R16

TP6

0.01µFC7

10.0kR11

GND

TP13

523kR2

2700pFC1

TP1

D5D-1N4148WS

D1D-1N4148WS

GND

1 23 45 67 89 10

11 1213 14

J3

22µFC11

22µF

C13

22µFC24

PGND

0.01µFC19

0.01µFC14

2.2µFC5

0.47µFC4

22µFC2

PinkD4

NT1

Net-Tie

GND PGND

3-24 Texas Instruments – 2014/15 Power Supply Design Seminar

Qi Power Transfer Communication Protocol

•  TX generates a shared magnetic field -  TX coil creates magnetic field -  Magnetic field induces current in RX coil

•  Communication in power field

-  TX waits until its field perturbed by RX

-  TX sends seek energy “ping”

-  TX waits for a digital response

-  If digital response is valid, transfer power

•  Power transferred at level needed

-  RX reports power received/needed

-  TX adjusts power based on RX feedback

-  If feedback is lost, power transfer stops

Apply Power

Co

nta

ct

Es

tab

lish

ed

Ex

ten

de

d

Dig

ital P

ing

Ping

Identification and

Configuration

Power Transfer

No Response

Abort Digital Ping

Power Transfer (PT)

Complete

PT Contact Violation

Unexpected Packet

Time-out

Power Transfer

Complete

Reconfigure

Selection

No PT Contact

Unexpected Packet

Transmission Error

Time-Out

From WPC Qi System Description. Part 1

Control

Linear

Controller

Voltage

Regulation / OV

Protection

Control and

Modulation

Synchronous

Rectifier

Rectifier

Voltage Battery/ChargerResonant

Transmitter

Resonant

ReceiverDriv

er

Control &

Demodulation

+

-

3-25 Texas Instruments – 2014/15 Power Supply Design Seminar

WPC RX Load Modulation

Integrated Transmitter IC Integrated Receiver IC

3-26 Texas Instruments – 2014/15 Power Supply Design Seminar

Measurement

•  Power transfer waveforms -  Coil resonance -  Harmonic content

•  Load response

•  Efficiency –

-  Loss contributors -  PCB coil vs. Litz

•  RX/TX communication

•  EMI, FOD

•  Spatial freedom VNA – Bode 100 – Coil gain/impedance characteristics MDO4104 – Mixed domain oscilloscope Differential voltage probe capable of > 40 V, current probe, IR probe

3-27 Texas Instruments – 2014/15 Power Supply Design Seminar

Reference Design Waveforms at 5 W Time and Spectrum Domain

Misaligned coils force operation closer to resonance Vpp_tx = 40 V, fSW = 135 kHz

RMS gain = 0.509

Centered coils force operation further from resonance

Vpp_tx = 20 V, fSW = 170 kHz RMS gain = 0.56

TX

TX Coil Harmonics TX Coil Harmonics

RX TX RX

3-28 Texas Instruments – 2014/15 Power Supply Design Seminar

Intelligent Voltage Positioning

Maximum data rate package during transition

240 ms

Dynamic Voltage Positioning

Load current step = 250 mA-0 A

3-29 Texas Instruments – 2014/15 Power Supply Design Seminar

Transient Load Response IOUT = 0 to 1 A

5 V TX Supply Current  

12 V TX Supply Current  

Voltage Response  

WPC Wireless Power RX Phone “Skin”  

3-30 Texas Instruments – 2014/15 Power Supply Design Seminar

Transient Load Step Response Litz TX Coil / PCB RX Coil

0 to 250 mA load step at ~ 1 A/µs

bq51013B based RX design 2.65 in x 1.35 in x 0.02 in

45 mm TX coil with shield

Eff

icie

nc

y (

%)

Output Power (W)

Litz TX Coil w/o

SEPIC Converter

Litz TX Coil w/SEPIC

Triple PCB Coil w/o SEPIC

80%

70%

60%

50%

40%

30%

20%

10%

0

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

3-31 Texas Instruments – 2014/15 Power Supply Design Seminar

System Efficiency – DC Input to DC Output PCB Coil vs. 105 Strand Litz Coil

3-32 Texas Instruments – 2014/15 Power Supply Design Seminar

Designing for Spatial Freedom Efficiency Across Charging Area

•  Efficiency map at a 5 W load measured over the PCB coil area •  +/- 40 mm in x-direction and 30 mm in y-direction, 5 mm steps

0.00% 0.00% 0.00% 45.23% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 44.95% 46.05% 0.00% 0.00% 0.00% 15

0.00% 0.00% 48.78% 51.77% 50.32% 45.38% 46.91% 50.38% 51.84% 50.05% 45.21% 46.49% 51.92% 52.46% 48.58% 0.00% 0.00% 10

0.00% 43.71% 51.37% 53.92% 52.23% 47.34% 52.23% 55.30% 56.12% 55.44% 51.05% 49.32% 53.11% 53.84% 51.24% 44.16% 0.00% 5

0.00% 44.74% 52.23% 54.55% 52.69% 48.95% 53.64% 56.73% 57.54% 56.72% 52.95% 49.69% 53.59% 54.54% 51.75% 45.64% 0.00% 0

0.00% 43.99% 51.58% 53.85% 52.56% 47.95% 51.06% 54.79% 55.37% 55.00% 50.74% 49.44% 53.06% 53.63% 50.99% 44.34% 0.00% -5

0.00% 41.57% 49.44% 52.08% 50.50% 45.28% 46.08% 50.08% 51.84% 50.23% 44.44% 46.61% 50.05% 51.68% 48.26% 0.00% 0.00% -10

0.00% 0.00% 42.12% 44.93% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 45.00% 44.81% 0.00% 0.00% 0.00% -15

-40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 (mm)

3-33 Texas Instruments – 2014/15 Power Supply Design Seminar

Design for Electromagnetic Compatibility

Optimized for EMC Non-Optimized Performance

GND Plane Under TX Coil TX Conductive Enclosure

WirelessReceiver

WirelessTransmitter

Common Mode Filter

Multilayer Electric Shield

3-34 Texas Instruments – 2014/15 Power Supply Design Seminar

Foreign Object Detection •  Depending on specific heat capacity,

foreign object temp rise can be > 60°C

•  Battery pack is especially sensitive

Where: →  P = Power dissipated in FO →  C = FO specific heat capacity →  M = FO mass →  t = time

•  Metal objects between TX and RX can induce eddy current losses

•  Field density of 5 W wireless chargers can result in significant eddy losses

ΔT= P× tC×m

1009080706050403020100

0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60

Tem

pera

ture

, deg

C

Power, W

AI Cu Fe Au

Temperature Rise for 1g of Material in 15s

TX 8,563

RX 5,000

04:00 04:20

04:40

05:00

10,000

8,000

6,000

4,000

2,000

0

Thr 1,900

Loss 1,316

04:00 04:20

04:40

05:00

2,000

1,500

1,000

500

0

Transmit & Receive Power (mW)

Loss vs. Threshold (mW)

3-35 Texas Instruments – 2014/15 Power Supply Design Seminar

Dynamic RX / TX Loss Accounting

45 mm FO placed adjacent to misaligned TX coil

TX & RX account for losses

Loss threshold set high

FO removed

FO placed next to TX coil, losses increase by > 1 W

FOD reaches 55 C in under 60 s

Transmit & Receive Power (mW)

Loss vs. Threashold (mW)

min:sec

min:sec

PDAn

Wired Model

Wireless Power Vision

Multi-ModeUniversal

WPT Transmitter

Charges All Compliant Devices

Intelligent WirelessPower Transfer

85% Efficient + Plus LowPower Shutdown Modes

Phone/PortableElectronic Device

~80%Full Load

Cha

rger

ICW

TPR

ecei

ver

Phone/PortableElectronic Device

Cha

rger

ICC

harg

erIC

WTP

Rec

eive

r

Customized Charging Cable

85% Efficient

Customized/Product SpecificAC to 5 VDC USB

Adapter

Limited Resource

AC

3-36 Texas Instruments – 2014/15 Power Supply Design Seminar

A Vision for Wireless Power Transfer

3-37 Texas Instruments – 2014/15 Power Supply Design Seminar

Summary

•  Market studies project rapid growth in wireless power technology

•  Wireless power transfer is useful when a wired solution is inconvenient, hazardous or impossible

•  WPT standards have emerged to accelerate growth, reliability, acceptance and safety in consumer electronics

•  Developing a wireless power solution does not require compliance to any standard other than those affecting consumer safety and EMC

•  Standard compliance may provide advantages in marketability

(interoperability), performance, reliability and time to market •  Achieving spatial freedom and good efficiency requires a deep

understanding of magnetic field theory

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