User Tools

Site Tools



Stan Zurek, FRM27/3.8/9, Encyclopedia Magnetica,
reviewed by Jeanete Leicht, 2014-01-21

FRM27/3.8/9 (also FRM27-3.8-9 or FRM 27 x 3.8 x 9) - a type of frame core made of soft ferrite, supplied by Ferroxcube.1)

The numbers refer to dimensions of the frame, so 27 = 27 mm, etc.

Helpful page? Support us!

All we need is just $0.10 per month. Come on… ;-)

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 BAR28/2.3/3.8 (or BAR28-2.3-3.8). The bar is marked with “28” because it is slightly longer (28 +/- 0.5 mm).

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.


Frame core (FRM20 shown for illustration) with the bar inserted into a bobbin
Disassembled frame core (FRM20), bar and bobbin

Core parameters

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

Symbol Parameter Value
Σ(l/A) core factor 5.56 mm-1
Ve effective volume 504 mm
le effective length 52.1 mm
Ae effective area 9.7 mm2
Amin minimum area 8.7 mm2
m mass of frame 1.6 g
m mass of bar 1.2 g

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

Material grade AL value effective permeability μe
3C90 350 nH +/- 20% 1550
3C91 420 nH +/- 20% 1860

Data sheets

Ferrite core FRM27/3.8/9 Ferroxcube

Copyrights © Ferroxcube

See also


1), 2), 3) Ferroxcube, Soft Ferrites and Accessories, Data Handbook, 2013
frm27-3.8-9.txt · Last modified: 2021/04/15 23:28 by stan_zurek

Disclaimer: This website is provided only for educational purposes. In no event the providers can be held liable to any party for direct, indirect, special, incidental, or consequential damages arising out of the use of this information.
Privacy and cookie policy (GDPR, etc.)