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    Ferrite beads for EMC testing

    I'm looking at the effect of ferrite bead on a pcb to improve Susepability when EMC testing.
    Looking at the curves on the data sheets .
    The peak resistance seems to be around the 2mhz range.
    Does this mean the ferrite bead will filter out frequencys around this range ie the higher the resistance( and reactance) the better the filtering??

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    Re: Ferrite beads for EMC testing

    There are quite different types of ferrite beads, e.g. beads on leads, surface mount beads, chip beads, wound beads, with different impedance and frequency range and current rating. You should narrow down the range you are talking about.

    Chip beads e.g. mostly have impedance maxima between 100 MHz and several GHz. Low MHz range would be rather expected for wound beads. Ferrite beads are usually inserted to increase the high frequency impedance of a connection wire or a circuit branch. They can be also part of low pass filters.



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    Re: Ferrite beads for EMC testing

    Quote Originally Posted by DIAGO1000 View Post
    I'm looking at the effect of ferrite bead on a pcb to improve Susepability when EMC testing.
    Looking at the curves on the data sheets .
    The peak resistance seems to be around the 2mhz range.
    Does this mean the ferrite bead will filter out frequencys around this range ie the higher the resistance( and reactance) the better the filtering??
    Attenuation is ratio of impedances with series path included with source.

    Although your values are missing, if the load is capacitive or low impedance a high series peak will improve attenuation at this peak.

    We can only guess how much without values.
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

    ... Tony Stewart EE since 1975
    - slightly north of Toronto



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    Re: Ferrite beads for EMC testing

    Quote Originally Posted by SunnySkyguy View Post
    Attenuation is ratio of impedances with series path included with source.

    Although your values are missing, if the load is capacitive or low impedance a high series peak will improve attenuation at this peak.

    We can only guess how much without values.
    I am testing an output of a hall effect sensor using a wurth ferrite bead 742792662.
    Testing to ISO11452-2 RF immunity,the immunity if 200Mz but passing at 400mhz upwards



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    Re: Ferrite beads for EMC testing

    If your load is high impedance, you better combine the ferrite bead with a shunt capacitor, to form a low pass filter.


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    Re: Ferrite beads for EMC testing

    I won't expect an UHF problem from your post #1 mentioning 2 MHz. If the problem is actually ferrite bead impedance > 200 MHz, you might refer to a HF ferrite bead like 742861210.

    An additional shunt capacitor should be helpful too, as mentioned by Volker.



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