Choosing the Right Ferrite: Comparing Core Materials

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Choosing the Right Ferrite Comparing Core
Materials
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Ferrite Cores
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Overview

• Only an EMC laboratory measurement can confirm
  that the ferrite is absolutely accurate. In most
  cases, calculating the dynamic impedance
  (transfer impedance) of an electronic circuit in
  the highest frequency range is not practical.
  This is dependent on a number of variables that
  are difficult to quantify mathematically,
  particularly in the HF range. However, an initial
  selection might be made based on experience and
  comparable measurements.

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How to Choose the Right Ferrite?

• In good designs, supply voltages or ground leads
  are in the range of 1 to 10O usable signal lines
  are between 50 and 100O and greater, depending on
  the application (e.g., bus systems such as CAN,
  SCSI etc.).
• Based on the nomogram, you may discover the
  desired ferrite impedance (ZF) starting with this
  transfer impedance (ZA or ZB) and the desired
  interference suppression. Knowing the ferrite's
  impedance, you can find the right ferrite for the
  job, such as a ferrite sleeve or an SMD ferrite.
• Wurth Electronics provides a Component Selector,
  a free software program that allows you to
  quickly and simply select SMD ferrites and other
  components, as well as simulate some of their
  functions.

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Comparison of Ferrite Core Materials

• Because of the frequency-dependent loss
  components, it's only practical to use the core
  materials for inductors within a specific
  frequency range. Beyond a typical frequency
  limit, core losses increase dramatically. The
  core material can be used as a filter element in
  this case.
• Conclusions
• Iron powder materials (Fe) can be employed as a
  pure inductor up to 400 kHz beyond that, the
  loss component dominates in R, which is present
  up to 10 MHz (more, depending on the core
  material). In the frequency range commencing
  about 20MHz and higher, the core is no longer
  effective.

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Continued..

• Manganese-zinc cores (MnZn) are inductive between
  20 and 30 MHz. In the frequency range starting at
  10MHz, increasing losses must be expected. The
  core material is no longer effective in the
  frequency band commencing about 80MHz.
• Nickel-zinc cores (NiZn) are inductive up to
  60MHz, but the core material becomes lossy above
  that, up to 1GHz and beyond.
• This qualitative analysis proves why nickel-zinc
  ferrites, in particular, have become
  well-established in the EMC range. It is the
  fundamental substance that acts as a filter over
  the broadest and most significant frequency
  range.
• MnZn ferrites have recently been used to decrease
  cable interference in the 150kHz to 30MHz range.
  The STAR-FIX LFS snap ferrites and the WE-AFB LFS
  ferrite sleeves are available from Wurth
  Electronics.

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Thank you

• If you need more assistance, you can feel free to
  connect with our experts who will take you
  through our wide range of ferrite products
  available for several applications. Contact us
  _at_cosmo ferrites ltd

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