How to Select and Use Ferrite Cores
How to Select a Ferrite Core 1
Shape factor of cores
Ferrite core impedance is based on shape factor, which is the ratio of the cross-sectional area (Ae) to average magnetic path length (Le). The shape factor, in conjunction with ferrite material, affects impedance performance of the ferrite core.
The chart in the below shows the shape factor of ferrite cores of the same material.
|No.||Part Number||Shape Factor||Magnetic Path Length (mm)||Cross section(mm2)|
The ferrite cores –cores 1, 2, and 3- listed on the chart correspond to the ferrite cores labelled in the below. Contrary to popular opinion, ferrite core 1 is the best performing, based on the given shape factor equation. Its shape factor is the highest of the three given ferrites.
Looking at the graph below, the core 1 has the highest impedance, while core 2 has the lowest impedance.
Note that only materials with the same permeability –the same material- should be compared against each other. If cores made of different materials are being compared, we cannot compare them using shape factor only. In order to choose the best ferrite core, shape factor should not be ignored.