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Ferrite Core Selection


Along with the selection of other components, ferrite core selection is also an important step in design process. Let see some of the important selection criteria;

Ferrite Core Selection

Below steps will clear the process of ferrite core selection;

1) Shape of cores

• Effective cross sectional area and Effective magnetic path length of ferrite core are the main parameters of ferrite core for deciding shape of cores.

Ferrite core selection
How to Select a Ferrite Core - Ae and Le value
• Cross section area (Ae) should be large and Magnetic path length (Le) should be small.

• Impedance of ferrite core depends on shape of ferrite core.

• Formula for calculating inductance using Ae and Le is;

L = N²µ (Ae / Le)

Where;
N = Number of wire turns
µ = Permeability

• As an example if we compare shown ferrite cores, core A (it’s Ae is large) is the best performing as compare to core B.

Ferrite core selection
How to Select a Ferrite Core - Shape of Core
• Core A has the highest impedance as compare to core B.

2) Winding turns on a core

• Impedance can be increase by number of turns within a core increase.

• If the working frequency is under 200MHz, ferrite core supporting lower frequency should be use. Also we can set turns.

• If the target frequency is over 200MHz, adding more ferrite cores or use a ferrite core which support’s higher frequency.

• We have to keep winding turns less, because more turns can create problem of stray capacitance.

• When working at higher frequency, this stray capacitance decreases impedance.

• This stray capacitance generates between individual wire turns of the coil. It didn’t cause energy loss but change behavior of coil by causing the coil to become self-resonant.

• More turns, more stray capacitance.

Ferrite core selection

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Conclusion

Important role in noise suppression is played by ferrite. Proper selection of ferrite will solve all the issues related to design and make circuit design easy.

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