Re: Ferrite rings

To: tesla-at-grendel.objinc-dot-com
Subject: Re: Ferrite rings
From: jim.fosse-at-bdt-dot-com (Jim Fosse)
Date: Wed, 06 Mar 1996 04:50:41 GMT
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>>From i_hopley-at-wintermute.co.uk Tue Mar  5 14:21 MST 1996

>Hi all
>

>To find out more i raided the scrap bin at work and came out with a well
>blown switch mode P.S.U.
Ian,

Question, were these from "IBM AT" power supplies? telecom power
supplies?

>
>Further investigation into ferrite materials and mixes revealed that
>peremebilitys range from around 40 (better than the best iron powder
>that i could find listed) right up to a material called " 'j'/75 " 
>with a value of 5000.
>
>Several of the rings in the psu gave very low readings so i assumed they were
>iron powder too. The rings that gave me the best reading were wound as a 
>common mode choke i.e with two equal numbered turns windings on either side of
>the core. 
> 
The low value cores were probably "gaped" cores for use as flyback
transformers or chokes that both have a high dc current.

The high value cores were from the common mode filter inductors, the 2
windings are effectively in anti parallel, for the mains current but
in parallel for the RFI. They can therefor have a high permeability
because the don't have to handle a large current.

jim