Importance of Impedance to find an Ferrite Beads

Thread Starter


Joined Mar 23, 2022
Hi everyone,

I will find a Ferrite for my board. I will know how vital a Ferrite's impedance is to do Electromagnetic compatibility? I mean, which role plays impedance of Ferrite generally? For example, when a Board works with a Ferrite with1300 Ohm, will it also work with 680Ohm impedance? Or should it be more than 1300 Ohm?

Thank you in advance; with the best regard


Joined Aug 27, 2009
It depends on a number of factors like the target frequencies, circuit design and the actual properties of the Bead. That one number doesn't tell all about each individual application.

To avoid misuse in your future ferrite bead needs, it is recommended that you always:

  1. Understand the noise problem within your circuit, including noise sources
  2. Choose the correct material behavior needed, e.g., high loss at low frequencies
  3. Determine the allowable trade-off for DC resistance and needed AC impedance
  4. Get the impedance curve and other data for the part to be used
  5. Don’t automatically use what has worked before
  6. Don’t assume that a ferrite bead will be the best EMI component to use
  7. If in doubt, contact your ferrite bead supplier as they will have EMI experts