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

2EPC – The Leader in GaN Technology Michael de Rooij and Yuanzhe Zhang www.epc-co.com

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

5EPC – The Leader in GaN Technology www.epc-co.com

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


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)


Gating Synchronization

Coil Current

Sensor

Magnitude and

zero cross detectIth

Icoil

Phase

shift To gate

driver

vc

RX Coil


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


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


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


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


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)


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


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


www.epc-co.com

Thank You


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

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