Ferrite beads in logic circuits

Discussion in 'General Electronics Chat' started by harrison2015, Apr 29, 2015.

  1. harrison2015

    Thread Starter Member

    Apr 22, 2015
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    I see these ferrite beads tied to +VCC like pull up resistors in logic circuits. What do these ferrite beads do that are also tied to +Vcc. The ferrite beads look like pull up resistors on the inputs and output of logic chips and also on the power pins of logic IC chips. The Ferrite beads smooth out the fluctuations, noise and ripple in the DC, anything else they do?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Ferrite beads are usually aimed at the higher (HF/RF) unwanted frequency pulses.
    Max.
     
  3. harrison2015

    Thread Starter Member

    Apr 22, 2015
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    the ferrite beads are in the VCC rails for TTL and CMOS logic
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    those are uses to filter out rfi/emi. prevent rf radiation. they started using them a little after pac man came out to filter rf radiation from the games. worked for that, didnt work for the game due to ringing of the ferite choke and shunt caps falsing inputs when exposed to static discharge.
     
  5. harrison2015

    Thread Starter Member

    Apr 22, 2015
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    how does ferrite beads filter out RFI/EMI frequencies? why can't a capacitor or inductor do this
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    because it adds inductance to a wire run through it. not a lot, but enough at higher frequencies where the intrferance is worst. using both caps and beads, usual.ly in a Pi configuration, works best. shunt cap, series inductor (ferite) and shunt cap.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    A ferrite bead IS an inductor.
    Max.
     
  8. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Hola Harri

    He explains the basics. This could help you.



    BTW, explore his list of videos. He is good.
     
  9. harrison2015

    Thread Starter Member

    Apr 22, 2015
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    I measured the ferrite beads on a huntron and the signature doesn't look like an inductor signature.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Would you deny these are (ferrite) inductors?
    [​IMG]

    Max.
     
    absf likes this.
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    The ferrite bead is roughly the same as a single turn choke on a toroid core - just a lot smaller.
     
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