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: xuguoying6102@163.com,{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 Publishing, 2001, ch.2, pp. 21-32. [2]Q. Wang, Switching Power Supply Design, 2nd ed. Beijing, China: Electronics and Industry Publishing, 2006, ch.1, pp. 12-20. [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, presented at the VPEC Seminar, 1993. [6]X. B. Ruan, Design of a ZVS-ZCS full-bridge DC/DC converter basedonResonantResetTechnology,inProc.4thAnnu.Conf. Power Electronics, Nanjing, 1997, pp. 141-145. [7]Q.Li,F.C.Lee,and M. M.Jovanovic,Designconsiderationof transformerDCBiasofforwardconverterwithactiveclamp reset, in IEEE APEC Proceedings, 1999, pp. 553-559. 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