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1、反激式變壓器設(shè)計步驟Step1.選擇CORE材質(zhì),確定△B本例為ADAPTERDESIGN,由于該類型機散熱效果差,故選擇CORE材質(zhì)應(yīng)考量高Bs,低損耗及高μi材質(zhì),結(jié)合成本考量,在此選用FerriteCore,以TDK之PC40orPC44為優(yōu)選,對比TDKDATABOOK,可知PC44材質(zhì)單位密度相關(guān)參數(shù)如下:μi=2400±25%Pvc=300KW/m2@100KHZ,100℃Bs=390mTBr=60mT@100℃Tc=215℃為防止X'FMR出現(xiàn)瞬態(tài)飽和效應(yīng),此例以低△B設(shè)計.選△B=60%Bm,即△
2、B=0.6*(390-60)=198mT≒0.2TStep2確定CoreSize和Type.1>求coreAP以確定sizeAP=AW*Ae=(Pt*104)/(2ΔB*fs*J*Ku)=[(60/0.83+60)*104]/(2*0.2*70*103*400*0.2)=0.59cm4式中Pt=Po/η+Po傳遞功率;J:電流密度A/cm2(300~500);Ku:繞組系數(shù)0.2~0.5.2>形狀及規(guī)格確定.形狀由外部尺寸,可配合BOBBIN,EMI要求等決定,規(guī)格可參考AP值及形狀要求而決定,結(jié)合上述原則,查閱
3、TDK之DATABOOK,可知RM10,LP32/13,EPC30均可滿足上述要求,但RM10和EPC30可用繞線容積均小于LP32/13,在此選用LP32/13PC44,其參數(shù)如下:Ae=70.3mm2Aw=125.3mm2AL=2630±25%le=64.0mmAP=0.88cm4Ve=4498mm3Pt=164W(forward)Step3估算臨界電流IOB(DCM/CCMBOUNDARY)本例以IL達80%Iomax時為臨界點設(shè)計變壓器.即:IOB=80%*Io(max)=0.8*3.16=2.528AS
4、tep4求匝數(shù)比nn=[VIN(min)/(Vo+Vf)]*[Dmax/(1-Dmax)]VIN(min)=90*√2-20=107V=[107/(19+0.6)]*[0.5/(1-0.5)]=5.5≒6匝比n可取5或6,在此取6以降低鐵損,但銅損將有所增加.CHECKDmax:Dmax=n(Vo+Vf)/[VINmin+n(Vo+Vf)]=6*(19+0.6)/[107+6*(19+0.6)]=0.52Step5求CCM/DCM臨ΔISB=2IOB/(1-Dmax)=2*2.528/(1-0.52)=10.53
5、3Step6計算次級電感Ls及原邊電感LpLs=(Vo+Vf)(1-Dmax)*Ts/ΔISB=(19+0.6)*(1-0.52)*(1/70000)/10=12.76uHLp=n2Ls=62*12.76=459.4uH≒460此電感值為臨界電感,若需電路工作于CCM,則可增大此值,若需工作于DCM則可適當(dāng)調(diào)小此值.Step7求CCM時副邊峰值電流ΔispIo(max)=(2ΔIs+ΔISB)*(1-Dmax)/2ΔIs=Io(max)/(1-Dmax)-(ΔISB/2)ΔIsp=ΔISB+ΔIs=Io(max)
6、/(1-Dmax)+(ΔISB/2)=3.16/(1-0.52)+10.533/2=11.85AStep8求CCM時原邊峰值電流ΔIppΔIpp=ΔIsp/n=11.85/6=1.975AStep9確定Np、Ns1>NpNp=Lp*ΔIpp/(ΔB*Ae)=460*1.975/(0.2*70.3)=64.6Ts因計算結(jié)果為分?jǐn)?shù)匝,考慮兼顧原、副邊繞組匝數(shù)取整,使變壓器一、二次繞組有相同的安匝值,故調(diào)整Np=60TsORNp=66Ts考量在設(shè)定匝數(shù)比n時,已有銅損增加,為盡量平衡Pfe與Pcu,在此先選Np=60T
7、s.2>NsNs=Np/n=60/6=10Ts3>Nvcc求每匝伏特數(shù)VaVa=(Vo+Vf)/Ns=(19+0.6)/10=1.96V/Ts∴Nvcc=(Vcc+Vf)/Va=(12+1)/1.96=6.6Step10計算AIRGAPlg=Np2*μo*Ae/Lp=602*4*3.14*10-7*70.3/0.46=0.69mmStep11計算線徑dw1>dwpAwp=Iprms/JIprms=Po/η/VIN(min)=60/0.83/107=0.676AAwp=0.676/4J取4A/mm2or5A/mm2
8、=0.1(取Φ0.35mm*2)2>dwsAws=Io/J=3.16/4(Φ1.0mm)量可繞性及趨膚效應(yīng),采用多線并繞,單線不應(yīng)大于Φ0.4,Φ0.4之Aw=0.126mm2,則0.79(即Ns采用Φ0.4*6)3>dwvccAwvcc=Iv/J=0.1/4上述繞組線徑均以4A/mm2之計算,以降低銅損,若結(jié)構(gòu)設(shè)計時線包過胖,可適當(dāng)調(diào)整J之取值.4>估算銅窗占有率.0.
