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Common Mode Filter Inductor Design Software
MAGNETICS® Common Mode Filter Inductor Design Software assists designers in making optimal, informed core and ferrite material choices. The software can accommodate user inputs of voltage, current, frequency, and/or desired impedance and will arrive at the best part number for the application.

Program features include:

  • Online Help to educate users with respect to important core and material characteristics, as well as offer detailed design assistance that thoroughly explains the design algorithm in place.
  • A comprehensive reference list of further information to help designers find answers to even more involved design issues.
  • Performance estimations of temperature rise, differential mode inductance, and filter cut-off frequency.
  • Component footprint size and wound core dimensions.
  • Hardware recommendations for devices to mount the common mode inductor to its PC board

To download this software, right-click on the link link below, and select "Save As" from the pop-up menu.  You will need software such as WinZip® to un-zip and install the program.  Get WinZip® now.

Download MAGNETICS Common Mode Filter Inductor Design Software (CMF-3.2, Feb 11 2001) (ZIP, 437 KB)

This software runs under Windows 95/98SE/NT/2000. Some Windows 95 users may experience problems due to an old release of the operating software.  Patches included in the ZIP files will fix some problems. If problems persist, try updating to the latest service pack, or contact a MAGNETICS  Application Engineer for more help.
Common Mode Filter Inductor Design
In a common mode (CMN) filter each winding of the inductor is connected in series with one of the input power lines. The connections and phasing of the inductor windings are such that the flux created by each winding appears to cancel (actually sums to zero within the core material) the flux generated by its opposing winding. The insertion impedance of the inductor to the input power line is therefore negligible.
The two figures below illustrate both the flux generated by the power lines and that induced by any common mode noise present on the lines. While 'power line' flux sums to zero (often thought of as 'canceling') because of its opposing nature, the common mode flux is left unopposed and therefore encounters the high reactive impedance of the core material. This high impedance offers filtering action against the common mode noise.



Figure 1: Filter Reaction to Line Current


Figure 2: Filter Reaction to Common Mode Noise Current

Toroidal cores are most popular for CMN filters as they are inexpensive and have very low leakage flux, and are featured in this design program. Toroids tend to be preferred due to the higher inductance allowed by having no inherent air gap at a mating surface can add as much as 30% more impedance at lower frequencies