a synchronous egan® fet class e rectifier for a highly resonant wireless power receivers ·...

A Synchronous eGaN® FET Class E Rectifier for Highly Resonant Wireless Power ReceiversMichael de Rooij and Yuanzhe Zhang

Outline

• Resonant wireless power receivers and

rectifiers

• Class E rectifier

• Synchronization

• Experimental results

• Conclusions

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Resonant Wireless Power Overview

3EPC – The Leader in GaN Technology Michael de Rooij and Yuanzhe Zhang www.epc-co.com

Amplifier

Coil

Tuning +

Supply Source

Source

Coil

Device

Coil

LoadDevice

Coil

Tuning

Rectifier

Full Bridge Rectifiers

4

• Simple

• popular choice at low

frequency

• High Losses at 6.78 MHz

EPC – The Leader in GaN Technology Michael de Rooij and Yuanzhe Zhang www.epc-co.com

Zcoil

Vrect

D1Cs

Cout Load

D2

D3 D4 Zcoil

VrectQ1Cs

Cout Load

Q2

Q3

Q4

Typical diode rectifier Synchronous rectifier

• More efficient

• Complicated gate drive

• Requires controller

• Operating power offsets benefit

Typical diode location: in series with output

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Class E Rectifiers

Zcoil

Cs

Zcoil

CsVDCVDC

[1] M. Liu, M. Fu, and C. Ma, “Parameter Design for a 6.78-MHz Wireless Power Transfer System Based on

Analytical Derivation of Class E Current-Driven Rectifier,” IEEE Trans. Power Electron., vol. 31, no. 6,

pp. 4280-4291, June 2016.

[2] S. Aldhaher, P. C.Luk, K. E. K. Drissi, and J. F. Whidborne, “High-Input-Voltage High-Frequency Class E

Rectifiers for Resonant Inductive Links”, IEEE Trans. Power Electron., vol. 30, no. 3, pp 1328-1335, Mar.

2015.

[1] [2]

• Source grounded GaN FET

• Simple gate drive

• High efficiency – no QRR, low COSS, CISS, RDSon

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Proposed Synchronous Class E

Rectifier

Vrect

Q1Csh

LexLck

VDSID

Cout

Zcoil

Cs

Ideal Waveforms

VDS ID

time

3.56 x VOut

V / I

50%

• RX coil zero current cross detect

• Output disabled at low current (<Ith)

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Gating Synchronization

Coil Current

Sensor

Magnitude and

zero cross detectIth

Icoil

Phase

shift To gate

driver

vc

RX Coil

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Gating Synchronization Detail

EN

SIG2

SIG1

C2

C3

C4

C5

L4

L5U1

OUT1

Vref

Vref

EN

RL1

SIG2SIG1

RS1 RS2RT0

D1 D2

a) Current sensing with waveform clipping

b) AC-coupled zero crossing detect

c) Magnitude detect

(a) (b)

SIG2

SIG1

C7

U2

Vcc

EN

C8D8

D7D6

C9 R4R4

R5

R6 R7

R8

(c)

• Transmit coil current: 1.375 ARMS

• Receive coil at 25 mm distance

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Experimental Setup

From

Coil

Synchronization circuit Class E rectifier

LexEPC2012C

Lck

DC

output

Clock outputs Clock input

Csh = 77 pF

Lex = 540 nH

Lck = 22 µH

• 60 V best in class Schottky diodes

• Full bridge Configuration

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Diode Rectifier for Comparison

Rectifier

Diodes

DC output

DC

Capacitors

From Coil

• Ith set to 100 mARMS

• Compensated for proper phase shift

• Both gate signals are off in “diode” mode

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Synchronization Circuit Test

vDS 5 V/div

icoil, RX

1 A/div

≈ 0 V

Icoil,RX = 99 mA rms, ‘diode’ mode Icoil,RX = 127 mA rms

vDS 5 V/div

icoil, RX

1 A/div

≈ − 2 V

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Measured Efficiency

83.0%

83.5%

84.0%

84.5%

85.0%

85.5%

86.0%

86.5%

87.0%

5 10 15 20 25 30 35 40

Effic

iency

Output Power [W]

Diode

Class E

Class E w/Gate drive

Total system efficiency at fixed 40 Ω DC load

Impact of

Operating power

• Fixed Icoil,TX = 1.375 ARMS

• Variable DC load (Resistance)

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Measured Efficiency

Rload

PFETloss

Rload_Design

Optimal DesignCan be improved

vDS

20 V/div 1 A/div

icoil,TXicoil,RX

Experimental Waveforms

14

Fixed Icoil, TX = 1.375 ARMS

40 Ω load, 38.2  VDC,36 W output

67 Ω load, 40 VDC,24 W output

EPC – The Leader in GaN Technology Michael de Rooij and Yuanzhe Zhang www.epc-co.com

Hard switching

vDS

20 V/div 1 A/div

icoil,TXicoil,RX

Conclusions

15

6.78 MHz eGaN FET synchronous class E rectifier

• More efficient than Schottky diode

• > 20% lower system power loss at > 35 W load

• Concept can be monolithically integrated

– Gate driver

– Signal detect

EPC – The Leader in GaN Technology Michael de Rooij and Yuanzhe Zhang www.epc-co.com

www.epc-co.com

Thank You

EPC – The Leader in GaN Technology Michael de Rooij and Yuanzhe Zhang www.epc-co.com