Re: magnetic core >Subject: magnetic core

• To: tesla-at-pupman-dot-com
• Subject: Re: magnetic core >Subject: magnetic core
• From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
• Date: Mon, 3 Feb 1997 10:38:02 +1200
• Subscriber: MALCOLM-at-directorate.wnp.ac.nz Sun Feb 2 17:55:11 1997

Hi John,
            Speaking from some switchmode power supply experience.....

> I have used ferrite to increase secondary inductance, to increase
> the coupling coefficient, and as a tuning aid, in tube coils.  I
> didn't really see much improvement in coil output.  Some have
> suggested that losses in the ferrite can be quite high (maybe
> higher in a tube coil due to higher operating Q?)--I welcome all
> viewpoints on this.

Ferrites are always more lossy than air. They will reduce the 
unloaded Q of a good coil - heating in the material is the telling 
point.

> Lou Balint of PA uses ferrite in his magnifier drivers, and he is 
> continuing to explore its possible benefits.  It is important to 
> have the "right" kind of ferrite for the frequency  and 
> permeability requirements.  

If I had a choice I would use the newish 3F3 (Philips) material. It 
is used in quasi-resonant supplies and switchers up to 1MHz or so.

> By using ferrite, we may be able to build more compact coils, I 
> would think.

Agree, esp. to elevate inductance of a dinky model. Drawback is that 
the material is a poor insulator.

Malcolm

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