反激式开关电源变压器设计实例

2.2 估算输入功率、输入电压、输入电流和峰值电流1)输出功率:Po=5V*1A+2*12V*1A+24V*1.5A=65W2) 输入功率:Pin=Po/η=65W/0.8=81.25W3) 最低输入电压:Vin(min)=AC90V*1.414=DC127V4) 最高输入电压:Vin(max)=AC240V*1.414=DC340V5) 最大平均输入电流:      Iin(max)=Pin/Vin(min)=81.25WDC127V=DC0.64A6) 最小平均输入电流:   Iin(min)=Pin/Vin(max)=81.25WDC340V=DC0.24A7) 峰值电流:Ipk=5.5Po/Vin(min)=5.5*65W/127V=2.81A2.3 确定磁芯型号尺寸按照表1,65W可选用每边约35mm的EE35/35/10材料为PC30磁芯磁芯Ae=100mm2, Acw=188mm2, W=40.6g2.4 计算一次电感最小值Lpri       Vin(min).Dmax      127*0.5 Lpri=                =             = 452*10-6H=452uH          Ipk.f         2.81*50*103此处选Dmax=0.5

2.5 计算磁芯气隙Lgap值      0.4πLpri.Ipk*108  0.4π*452*10-6*2.81*108Lgap=                  =                       = 0.04cm=0.4mm          Ae B2max          1*(2000)2 查表,EE35/35/10  AL=120uH/N2  Lgap约为0.5mm2.6 计算一次绕组最大匝数Npri         Lpri    452*10-6 Npri =       =           = 61.4匝   取Npri=62匝          AL     120*10-92.7 计算二次主绕组匝数NS1(NS1为DC+5V绕组)            Npri(V01+VD)(1-Dmax)    62*(5+0.7)*(1-0.5)Ns1=                       =                    = 2.78匝          Vin(min)Dmax            127*0.5          取Ns1=3匝此处整流二极管压降VD=0.7V
  2.8 计算其它次级绕组匝数                   (Von+VDn)Ns1                  Nsn =                                    V01+VD1                            (12+0.7)*3   +12V      Nsn =              = 6.68匝     取7匝                     5+0.7                                       (24+0.7)*3   +24V     Ns24 =              = 13匝     取13匝                     5+0.7
2.9 检查相应输出端电压误差                 Vsn        δVsn%=(( =      *Ns’n-Vsn)/Vsn)*100%                                            Nsn                   12 +12V δVS12%=(( =      *7-12)12)*100%=4.79%                 6.68                   24 +24V δVS24%=(( =      *13-24)24)*100%=0 %                  13  电压误差均符合要求.
一次绕组:dwp = 1.13  0.64 = 0.52      取0.5mm                        3 二次绕组:+5V dwn1 = 1.13  1  = 0.65      取0.5mm   6股                           3               +12V,       0.5,        4股         -12V,       0.5,        2股         +24V,       0.5,        2股         偏置,       0.4,       单股
2.11 计算变压器损耗1)铜损:Pcun = NnV* MLT*Rn)In2              MLT = 2E+2C=2*25.27+2*9.35=69.24mm初级铜损: Pcup=(62*69.24*10-3*0.085)0.642 =0.15W   149W次级铜损: Pcu+5V=(3*69.24*10-3*0.085/6)32 =0.026W  0.07W          Pcu+12V=(4*69.24*10-3*0.085/4)22 =0.024W  0.06W          Pcu+24V=(6*69.24*10-3*0.085/2)12 =0.018W  0.05W           Pcu-12V=(7*69.24*10-3*0.085/2)12 =0.021W  0.06W总铜损:      Pcu=0.15+0.026+0.024+0.018+0.021=0.239W  2) 铁损:PC30磁芯在50KHz,2000G时损耗=250mw/cm3=52mw/g         Pc=250*10-3 *40.6 =2.1W                4.8

为什么峰值为：峰值电流:Ipk=5.5Po/Vin(min)=5.5*65W/127V=2.81A 

我看到的DCM 很多资料都是： Ipk=2*P0/(3*Dmax*η*Vmin)  你这5.5怎么来的？

5.5PO正常呀，你看一下开关电源第二版就知道了，反激是5.5.BUCK.2.4

其实我，很是明白的是铜损与铁损的算法

你好，我想问，你的工作磁通密度:Bmax=2000G是怎么得知的》