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  • Fair-Rite-Bridget
    Member
    Post count: 17

    Hi Interested Parties:
    The purpose of this topic is to provide an open forum to allow users of Fair-Rite’s products to share information, opinions, and experiences about audio and home entertainment devices as applies to Fair-Rite and ferrite products. The topic is Audio and Home Entertainment, but this forum can be utilized for addressing other areas for potential ferrite use within the home which are not covered in other forum topics on Fair-Rite’s website.

    Bruce Sparrow
    Member
    Post count: 24

    A gentleman asked my advice on how to reduce noise spikes he say on his +/- analog voltage rails. The spike were occurring at 120kHz and causing beat frequency problems.

    Hello,
    At 120kHz there are two possible ways to deal with the problem. The first is a classic filter where an inductor blocks the unwanted noise signal. We know that these pulses contain a lot of harmonics so the inductor would need to act as an inductor beyond a couple megahertz. Our 43 material provides good permeability up to this band and then becomes lossy – which is a good thing. We make a lot of different product with that material for you to choose from.

    Alternately you can use a suppression material to ‘consume’ the energy in the spike. Our 73 material is designed to become lossy at a low frequency. At the 120kHz is will add a good amount of resistive impedance out to about 100mHz. Our product offering has lots of smaller bead products made from this material. So the way this works is that the material acts like a frequency dependent resistor that has resistive losses and insertion impedance at these frequencies. Exactly how many ohms you need is a function of amplitude and source and load impedance. EMI gets attenuated and the loss ends up as tiny amounts of heat dissipated in the ferrite material.

    If this is common mode noise, and it probably is because those are linear voltage regulators, then the positive and return conductors can go through the ferrite and you don’t have to worry about saturation.

    Unfortunately most EMI components are great at helping with 10mHz and higher so 0805 SMD components are not going to help you much. You are going to need a ferrite bead. I’d start with the second option.

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