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i
PANEL
金属磁粉芯 在高效率电源模块的PFC应用 分析
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开关电源磁性器件选型 没有最好 只有最优. 选型的基本原则: 体积 效率 成本 以上三者的调节,优化 到平衡.
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1.磁性材料分類: 磁心材料主要分为:软磁材料和硬磁材料 (1). 软磁材料的主要特点是易磁化易退磁,大部分的软磁材料常容易被磁化,施加很 小的磁场,即可使之磁化而得到磁化量,一旦外加磁場消失,感应磁化隨即消失,材料 本身无保持磁化的能力,此类材料被称为软磁材料。 (2). 硬磁材料的主要特点与软磁相反,经磁化后当外磁场去除时磁性並不完全消失, 而能在较長時間內仍保留相当強的磁性，此类材料被称为永磁材料。
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Soft Magnetic Material 软磁材料
n
Powder Cores粉芯磁芯
Iron core MPP High Flux SENDUST FeSi 铁粉芯 MPP HF FeSiAl FeSi6.5%
n
n
Ferrites铁氧体 MnZn NiZn Tape Wound Cores带绕磁芯
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Magnetic Hysteresis loop 磁滞回线
Domains aligned
Bs, Br, Hc, μi, μa(max) and core loss are function of temperature and frequency
均是温度与频率的参数
B Magnetic Flux Density 磁通密度
Bs Saturation Flux Density 饱和磁通密度 其大小取决于于 材料的成分,它对应的物理状态的材料内部的磁化矢量整齐排列 Br Remanence 剩磁感应强度,是磁滞回线上的特征参数H 回到0时的B值,矩形比Br/Bs. H Hc μi Magnetic Field Strength 磁场强度 Coercive Force 矫顽力 表示材料磁化难易程度的量 Initial Permeability 初始磁导率
μa(max) Maximum Amplitude Permeability 最大增量磁导率
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Magnetic Fields 磁场
A magnetic field is generated when a charge is in motion ? Can be a current flowing in a conductor
H r
i
安培环路积分定律
Ampere’s law
Ni = ∫ H ? dl Ni H= l
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Magnetic Definitions 磁定义
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Powder Core and Gapped Ferrite Comparison 磁粉芯与气隙铁氧体对比
1.0 Per Unit of Initial Permeability 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1 10 100 DC Magnetizing Force (Oe) 1000
MPP High Flux SENDUST Ferrite
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Gapped ferrite eddy Losses 铁氧体气隙引入涡流损耗
The gapped flux bowing into the space occupied by copper conductor generates eddy current losses in the coil.
气隙的漏磁通将对线圈的铜 线进行切割产生涡流损耗
The eddy losses can easily exceed the AC core losses.
这种涡流损耗将会增加交变 的磁芯损耗
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Distributed gap Powder Core均匀气隙磁粉芯
Distributed gap
Ignore coil eddy losses
Magnetic alloy Non-magnetic insulating layer
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Core Loss 磁芯损耗
Total magnetic core losses are mainly a combination of hysteresis loss and eddy current losses 磁材的总体磁芯损耗主要由磁滞损耗与涡流损耗组成 Pcore= Ph+Pe Steinmetz constants, curve fit: 磁材损耗的公式如下，通过损耗曲线进行拟合而成，故X与Y参数与 材料有关 Pcore=CFSWXBY Ve x and y are material dependent
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金属磁粉芯对比
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Permesbility versus DC Bias Curves:
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Core Loss Curves:
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Powder Cores – Price
n n n n n n n n
Iron Powder Ferrite PPI NPS/ (Sendust) PPF/PF NPF/PMF High Flux (HF) MPP
Lowest Cost
Highest Cost
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PFC Inductor Design
PFC电感器设计
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BOOST Circuit
Work voltage (min) Vinmin Output Power Module efficiency Work frequency Duty (min) Pout 175VAC 3000W 96.5% 50kHz 40%
η
F D
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一.感量计算：
Pout Irms Max = ηV inmin Ipk=
2
Irms Max = Ipk=
2
3000 98%* 175
= 17.5A
x Irms Max
x 15.7A = 25 A
Wave dI if Ipk 20% dI=0.20 x Ipk Vinmin xD F dI
Wave dI if Ipk 20% dI=25A x 20% = 5 A 175 x 40% = 396μH 50 x 5A
L=
2
L=
2
Lr=L/2=396μH/2=198μH
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二.空间考量：
OD:1.84 inch (46.74mm) ID:0.95 inch (24.13mm) OD:0.71 inch (18.03mm)