Ferrite materials for electromagnetic interference suppression have significant losses. Inductors made with such ferrite cores exhibit characteristics closer to resistors. To fully utilize the performance of ferrite, special attention should be paid to the following aspects:

1. Ferrite core toroid effects are related to circuit impedance.

In typical product manuals for ferrite materials, the insertion loss of the ferrite material is not provided, but the impedance is. The higher the impedance of the ferrite material, the better the filtering effect.

2. The Impact of Current

When a larger current flows through the wire passing through the ferrite core, the low-frequency insertion loss of the filter decreases, while the high-frequency insertion loss changes little. To avoid this situation when using the power line, both the power line and the return line can be passed through the ferrite core simultaneously.

3. Selection of Ferrite Materials

Select different ferrite materials with varying permeability based on the frequency of interference to be suppressed. The higher the permeability of the ferrite material, the greater the impedance at low frequencies and the smaller the impedance at high frequencies.

4. Determination of Ferrite Toroid Dimensions

The larger the difference in the inner and outer diameters of the ferrite magnetic ring, the longer the axial length and the higher the impedance. However, the inner diameter must be tightly wrapped around the wire. Therefore, to achieve greater attenuation, it is recommended to use a magnetic ring with a larger volume, while ensuring the inner diameter is tightly wrapped around the wire.

5. The turns of the common-mode choke

Increasing the number of turns through the magnetic rings can enhance the impedance at low frequencies; thus, by winding more turns, impedance can be effectively increased to achieve the desired effect. However, due to the increased parasitic capacitance, the impedance at high frequencies may decrease. When a wider interference frequency band needs to be suppressed, different numbers of turns can be wound on the two magnetic rings.

6. Number of ferrite magnetic rings on the cable

Increasing the number of ferrite magnetic rings on the cable can enhance low-frequency impedance, but it will reduce high-frequency impedance. This is due to the increased parasitic capacitance.

7. Ferrite toroid placement

Position the magnetic rings as close as possible to the cable进出口 on the shielded enclosure.

8. Better performance when used with capacitive filter connectors.

Due to the ferrite bead's effectiveness being dependent on the circuit's impedance, the lower the impedance, the more pronounced the bead's effect. Therefore, when the original cable ends are fitted with capacitive filter connectors, the impedance is low, making the ferrite bead's effect more noticeable.

Coercivity cores' coils still act as inductors at lower frequencies. For a filter circuit composed of a single inductor, the cutoff frequency is: Fco = 1 / (2πRsL), where Rs is the series value of the original circuit impedance and the load circuit impedance.