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Stan Zurek, FRM20/5/15,, {accessed 2020-11-26}
reviewed by Jeanete Leicht, 2014-01-21


FRM20/5/15 (also FRM20-5-15 or FRM 20 x 5 x 15) - a type of frame core made of soft ferrite, supplied by Ferroxcube.1)

The numbers refer to the dimensions of the frame, i.e. 20 = 20 mm.

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The core comprises a cuboid bar, which slides into a bobbin. The outer frame of the core is assembled on top of the bobbin.

The bar has a symbol BAR20/3/5.5 (or BAR20-3-5.5).

The relative winding width is longer than in most of other ferrite cores, which allows for the bobbin to have multiple sections. The manufacturer offers the multiple-chamber bobbin, but there is no indication of how all the parts should be held together (e.g. a clip).

As of 2013 the core was offered in two materials: 3C90 and 3C91.


FRM20 with the bar inserted into a bobbin

by S. Zurek, Encyclopedia Magnetica, CC-BY-3.0

Disassembled FRM20

by S. Zurek, Encyclopedia Magnetica, CC-BY-3.0

Core parameters

The table below lists the core set parameters as given by Ferroxcube.2)

Symbol Parameter Value
Σ(l/A) core factor (C1) 3.29 mm-1
Ve effective volume 655 mm
le effective length 46 mm
Ae effective area 14 mm2
Amin minimum area 7.4 mm2
m mass of frame 2.1 g
m mass of bar 1.5 g

The values were measured for frame with a bar core, without an air gap.3)

Material grade AL value effective permeability μe
3C90 500 nH +/- 25% 1310
3C91 600 nH +/- 25% 1570

Data sheets

Ferrite core FRM20/5/15 Ferroxcube

Copyrights © Ferroxcube

See also


1), 2), 3) Ferroxcube, Soft Ferrites and Accessories, Data Handbook, 2013
frm20-5-15.txt · Last modified: 2020/07/19 00:54 by stan_zurek

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