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FINEMET® COMMON MODE CHOKE
   

FINEMET® common mode choke cores have high permeability which makes them suitable for use in common mode chokes and superior to the material most commonly used, Mn-Zn ferrite. The followings are the advantages of FINEMET® over Mn-Zn ferrite cores.

1. The real part of complex permeability (µr ') at 100kHz and 20ºC reaches more than twice as high as that of Mn-Zn ferrite cores. The impedance relative permeability (µrz) including imaginary part of complex permeability (µr '') reaches more than four times as high as that of Mn-Zn ferrite cores. Consequently, the cores shows following benefits when compared with a same size Mn-Zn ferrite core (Table 1, Figure 1, Figure 2.

  • It allows four times higher impedance when applied to the same number of winding turns.
  • FINEMET® can be reduced to 1/2 winding turns to obtain same impedance value as a Mn-Zn ferrite core in lowfrequency. Consequently, it reduces stray capacitance significantly. As a result, impedance in high frequency range becomes large.

2. Frequency dependence of initial permeability (µr ',) is not significantly affected by temperature change. Consequently, common mode chokes with FINEMET® cores have low temperature dependence of inductance and impedance over a wide frequency and temperature range (Figure 3, Figure 4).

  • FT-3 material is the improved version of FT-1 material.
  • FT-3 material has low saturation magnetostriction constant (10-7 order), as a result has less audible noise emission.
 
FT-1KM
FT-3KM
Mn-Zn ferrite
Initial Permeability at 100 kHz , µr
20°C
16,000
17,000
5,300
100°C
16,300
18,000
7,000
Impeadance permeability at 100 kHz , µrz
20°C
25,700
26,900
5,300
100°C
26,300
27,100
7,000
Saturation magnetic flux density Bs * (T)
20°C
1.35
1.23
0.44
100°C
1.30
1.20
0.27
Residual magnetic flux density Br * (T)
20°C
0.81
0.62
0.10
100°C
0.73
0.59
0.06
Coercive Force Hc * ( A/m)
20°C
1.3
2.5
8.0
100°C
1.4
2.7
4.9
Curie temperature Tc(°C)
570
570
150
Saturation Magnetostriction
+2.3
~0.0
-1.1
Electrical Resistivity
1.1
1.2
1.0 X 106
Density d(kg/m3)
7.4 X 103
7.3 X 103
4.85 X 103

* DC magnetic properties 800 A/m

µrz, µr ', and µr '' for FINEMET® FT-1KM
Figure 1. µrz, µr ', and µr '' for FINEMET® FT-1KM
µrz, µr ', and µr '' for Mn-Zn ferrite
Figure 2. µrz, µr ', and µr '' for Mn-Zn ferrite

Temperature dependence of impedance permeability (µrz)for FINEMET® FT-1KM
Figure 3. Temperature dependence of impedance permeability (µrz)for FINEMET® FT-1KM


Temperature dependence of impedance permeability (µrz)for Mn-Zn ferrite
Figure 4. Temperature dependence of impedance permeability (µrz)for Mn-Zn ferrite


 
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