Current Doubler Rectifier for High Power and Low Voltage DC/DC
Converter Applications Guoying Xu, Haisheng Yu, Huachang Zou, Hao
Yang, and Ming Cheng Sichuan Institute of Solid State Circuits,
China Electronics Technology Group Corp., Chongqing, China Email:
[email protected],{yuhaisheng, zouhuachang, yanghao,
chengming}@ sisc.com AbstractTherectifierhasimportantinfluenceona
DC/DCconverterscharacteristicsincludingtheefficiency,
theoutputvoltagerippleandthedynamicbehavior.By
analyzingthedifferencebetweenthecentertrapped
rectifierandthedoublecurrentrectifier,thisdocument
explainsanddemonstratestheadvantageofthecurrent doubler rectifier
for DC/DC converters with especially high power but low output
voltage which mean very high output current. I ndex
Termscurrentdoublerrectifier,DC/DCconverter, high power, low
voltage I.INTRODUCTION Along with the development of industry,
avigation and spaceflight, there are more and more requirement for
high powerdensityDC/DCconverterswhichmakethe
electronicsystemssmaller,lighterandmoreefficient. One of the most
pivotal factors which restricts the power
densityofDC/DCconvertersisefficiencybecausethe
heatresultedfromthepowerlossesbringsserious
drawbacktothereliabilityandlifetimeofthe
converters[1],[2].Rectifierisanintegrantpartofa DC/DC converter but
it produces nearly 40 percent of the powerlosses and also affect
the dynamic response. So it is necessary togo deep into the
rectifiers especiallyfor the
highpower,lowoutputvoltageandhighoutputcurrent
DC/DCconverters.Synchronousrectificationisquite
applicableinhighcurrentapplicationsasitcanreduce conductinglosses
largely[3]-[5]. Furthermorethecurrent doubler rectifier gives
advantages when the current ripple is low. The goal of this work is
toanalyzing the advantage and disadvantage between center trapped
rectifier and current
doublerrectifierandfindoutthemoreconformableone
forhighcurrentapplications.Inthispaper,a500watts
DC/DCconverterbasedonfullbridgetopologyis discussed. II.HIGH POWER
DC/DC CONVERTER BASED ON FULL BRIDGE TOPOLOGY
Fortheapplicationswhentheinputvoltageisquite
high,forexample,300volts,thefullbridgetopologyis
Manuscript received June 26, 2013; revised August24, 2013.
oneofthemostsuitedchoicebecausethevoltagestress on each switch is
equal to the input voltage, which make it able to use lower voltage
degree MOSFETs and reduce the power losses. Q1D1 C1Q2D2 C2Q3D3 C3Q4
D4 C4+-Vin+-UG1+-UG3+-+-UG2 UG4Ip+ - UABT Figure.1Sketch map of the
full-bridge DC/DC converter UG1UG2UG3UG4UABIpdead time t1dead time
t2phase-shiftedphase-shiftedtttttt Figure. 2Typical waveforms of
the full-bridge DC/DC converter
ADC/DCconverterbasedonshift-phasefullbridge
topologyisshowninFigure1[6],wherethecapacitors
C1~C4aretheoutputcapacitanceoftheMOSFETs Q1~Q4and thediodes
D1~D4could bethe body-diodes
orseparatediodes.TheMOSFETsaredrivedbya Lecture Notes on Photonics
and Optoelectronics Vol. 1, No. 2, December 201348 2013 Engineering
and Technology Publishingdoi:
10.12720/lnpo.1.2.48-51controllerthateachtwoonthesamelegare180phase-shiftedandthephasedegreebetweenthetwo
MOSFETscatercorner,,isshiftedfrom0to180whichdeterminesthedutyofthefull-bridgeDC/DC
converter.Ineachcycle,thepowertransformerTis magnetized
bidirectionally and the voltage on the primary
sideissymmetrical.Thetypicalwaveformsofthe converter is represented
in Fig. 2. AsisshowninFig.2,thetransformerworks symmetrically
during each cycle, a rectifier which is able
totransferenergybidirectionallyisneeded.Eithera
centertrappedrectifieroracurrentdublerectifieris
competent.Forhighoutputcurrentapplications,the
synchronousrectificationthatmakeuseoflow
on-resistanceMOSFETsinsteadofSchottkydiodesor
fast-recoverydiodespoduceslessconductinglossesthat
isapplicabletoboththecentertrappedrectifierandthe current duble
rectifier. III.COMPARISON BETWEEN CURRENT DOUBLER RECTIFIER AND
CENTER TRAPPED RECTIFIER A.Rectifiers Comparison TLC LoadSR2SR1Io
Io a) Center trapped rectifier TL1CLoadSR2SR1Io IoL2IL1IL1 b)
Current doubler rectifier Figure. 3Sketch map of the two different
rectifiers Acurrentdoublerrectifierandacentertrapped rectifier are
shown in Fig. 3. The current doubler rectifier
isdifferentfromthecentertrappedrectifierbythe
structurethatwithonlyonesecondarywindingandtwo separate output
inductors which make it three advantages
thanthecentertrappedrectifier.Firstly,astwooutput
inductorsharethetotaloutputcurrentthatmeansIL1
plusIL2equalsIo,duringeachhalfcyclethecurrent flows in
thesecondarywinding is just 50% of thecenter
trappedrectifier.Secondly,therearelesshighcurrent connections in
the current doubler rectifier which make it
easierforthePCBdesignandminimizetheelectro magnetic interference.
Thirdly, the two separate inductors share in the high output
current so each one is in smaller
sizeandthelossesaresharedthatgivestheconverter better heat
distributing. Forfurthercomparison,asamephase-shiftedfull
bridgeDC/DCconverterisdicussesdandtheduty,the
switchingfrequency,thecapacitance,theinputand
outputvoltageareidenticalandsincethetwooutput
inductorsinthecurrentdoublerrectifierareparallelthe
inductanceistwotimesthanthatofthecentertrapped rectifier. The
characteristics interrelated with the rectifier include the current
ripple, the slew rate and power losses
oftheinductorandtheperformanceofthetransformer and the switches.
B.Inductor Comparison Insteadyworkingmode,theoutputinductorLofthe
center trapped rectifier is current-balance as Eq.(1). In the
sameway,boththeinductorsL1andL2ofthecurrent
doublerrectifiersatisfyEq.(2).Sothevoltageonthe secondarywinding of
thecurrent doubler rectifier is two times of thatof thecenter
trapped rectifier,Vsec=2
Vsec1.Itisdemonstratedthatthetotalslewrateof
currentIL1andIL2isequaltothatofIL,expressedby Eq.( 3) to Eq.( 8).
sec1 sec1T( ) T (1 2 ) 22o oV V d Vo d V V d (1) sec sec( ) T (1 )
To oV V d Vo d V V d (2) sec1 sec1 sec1 sec1( )2 (1 2 )or CTV V V V
d V dkL L L (3) sec1( )2of CTV V dkL L (4) 1sec sec sec sec( )1 1
1(1 )or L LV V V V d V dkL L L 2(5) 1sec( )1 1of L LV V dkL L 2 (6)
1 1sec( ) ( ) ( )1(1 2 )r CD r L L f L LV dk k kL 2 2 (7) 1sec( ) (
)122f CD f L LV dk kL 2 (8) where:
kr(CT)=therisingrateofthecurrentoftheinductorin center trapped
rectifier kf(CT)=thefallingrateofthecurrentoftheinductorin center
rectifier kr(L1L2) = the rising rate of the current of the
inductors in current doubler rectifier kf(L1L2)=thefalling rateof
thecurrent of theinductors in current doubler rectifier kr(CD) =
the rising rate of the total current ripple in center trapped
rectifier kf(CD)=thefallingrateofthetotalcurrentripplein center
rectifier Lecture Notes on Photonics and Optoelectronics Vol. 1,
No. 2, December 201349 2013 Engineering and Technology
PublishingILVp a) Center trapped rectifier IL1+IL2IL1IL2Vpt b)
Current doubler rectifier Figure 4. Current ripple of the two
rectifiers IoIoVSECTdTdTILI/tdTdTttt a) Center trapped rectifier
IoVSECTdTdTdTIL1+IL2I/tIL1IL2dTttttt b) Current doubler rectifier
Figure 5. Load step response of the two rectifiers
Itisprovedthatbytheequationsabovethatthetotal
currentripplewaveformsandloadstepresponseare
identicalinboththecentertrappedrectifierandthe
currentdoublerrectifierwhichareshowninFig.4and Fig. 5.
Toemphasizethedifferencesofpowerlossesofthe
inductorsineachrectifier,webuildFEA(finiteelement
analysis)modelsoftheinductorsinwhichhigh
frequencyeffectsareregarded.Ontheassumptionthat
theareaandvolumewitheachrectifieraresimilar, several specifications
ofI/Io such as 5A/10A, 5A/50A, 1A/10A, 1A/25A are computed and the
results show that there are lower losses in center trapped
rectifierfor most casesandonlyforverylowI/Ioratioslike5A/50Athe
current doubler rectifier present less losses. C.Transformer
Comparison The losses of the transformer relate to the turns and
the configuration of thewindings and the current flowing in. As
introduced before, the frenquency, duty and size of the
transformersareconsistantinboththecurrentdoubler rectifier and the
center trapped rectifier so the magnetism flux and the core losses
are almost equal. As is shown in Fig. 6, with the same average
value but the AC current in
thecurrentdoublerrectifierislargerthanthatofthe certer trapped
rectifier which means larger AC losses. On
theotherhand,itismorepossibletoachievebetter interleaving
configuration and higher coupling coefficient
inthecurrentdoublerrectifierwhichreducethecurrent ringing at each
switching time[7]. tIPRIMVPRIMISEC1I/nCTIo/nCT-Io/nCTIIoIo/2tt a)
Center trapped rectifier
IPRIMISECI/nCDIo/2nCD-Io/2nCDI-Io/2Io/2VPRIMttt b) Current doubler
rectifier Figure 6. Current waveforms of the rectifiers Lecture
Notes on Photonics and Optoelectronics Vol. 1, No. 2, December
201350 2013 Engineering and Technology
PublishingAccordinglytheinferior positiondueto theAC losses
ofthetransformerandtheturn-offlossesofthe
MOSFETsinthecurrentdoublerrectifierwouldbe
compensatedwhentheoutputcurrentisextramlyhigh and the current
rippleIo is low. For example, Io = 25 A andIo = 2A. IV.CONCLUSION
For high power and high current DC/DC converters the rectifier is
one of the major parts that has important effect
ontheconverterincludingtheefficiency,currentripple, dynamic
response, size,configuration, EMI and lifetime.
Boththetwosynchronoursrectifiersarecommendedin
highoutputcurrentapplicationsandthecurrentdoubler
rectifierismoreapplicablewhenlowcurrentrippleis
required.Itisdemonstratedthatwhilethecurrentripple
anddynamiccharacteristicsareidentical,abetter
interleavingtransformercanbeachievedandreducethe
turn-offlossesandAClossesinthecurrentdoubler
rectifier.Futhermorethetwoparallelinductorssharing theoutput
current produce less losses andamelioratethe heat distributing
which make a smaller size possible. REFERENCES
[1]Z.S.ZhangandX.S.Cai,PrincipiumandDesighofSwitching
PowerSupplies,1sted.Beijing,China:ElectronicsandIndustry
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Supply Design, 2nd ed. Beijing, China: Electronics and Industry
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[3]L.P.Jin,Designofasingle-endedforwardDC/DCconverter based on
resonant reset technology, Micro-Electronic, vol. 42, pp. 124-128,
July 2012. [4]C. Blake, D. Kinzer, and P. Wood, Synchronous
rectifiers versus
schottkydiodes:Acomparisonofthelossesofasynchronous rectifier
versus the lossesof a schottky diode rectifier, presented at the
IEEE Applied Power Electronics Conference, 1994.
[5]M.M.Jovanovic,J.C.Lin,C.Zhou,M.Zhang,andF.C.Lee,
Designconsiderationsforforwardconverterwithsynchronous rectifiers,
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ZVS-ZCS full-bridge DC/DC converter
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GuoyingXuwasborninChongqing,China,in
1983.ShereceivedtheMastersdegreein
electronicengineeringfromtheHarbinInstitude of Technology, Harbin,
China, in 2007. SheisaseniorengineerofSichuanInstituteof
SolidStateCircuits,ChinaElectronics
TechnologyGroupCorp..Hercontributionsare focused in the field of
power supplysystems for telecom,aerospace,automotiveandmedical
applications.Herresearchinterestsarehigh power density and magnetic
components. Lecture Notes on Photonics and Optoelectronics Vol. 1,
No. 2, December 201351 2013 Engineering and Technology
Publishing