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Re: Ferrite chokes & saturation - why toroids?
From: Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: Monday, November 24, 1997 9:42 PM
To: Tesla List
Subject: Re: Ferrite chokes & saturation - why toroids?
Hi Adam,
> From: Adam[SMTP:absmith-at-tiac-dot-net]
> Sent: Monday, November 24, 1997 10:26 AM
> To: Tesla List
> Subject: Re: Ferrite chokes & saturation - why toroids?
<snip>
> I noticed you mentioned that an iron powder toroid would need many turns
> of wire for the proper inductance, due to low permeability of the core.
> My question is: isn't it a real pain to wind wire through a toroid?
Yes. Most small toroidal cores are used for low inductance chokes or
energy storage apps (you get them in forward switchmode power
supplies - iron powder because of the high DC level in the windings).
Other than that, high permeability cores are used in common mode
filters where cores are operated at zero core flux in differential
mode.
> I
> have been using ferrite "U" cores taken from old B&W TV transformers,
> winding each half separately, and then Krazy gluing them together (with
> spacers). Also, ferrite is usually gapped between the halves as a
> measure against flux saturation at DC and very low (60Hz?) frequencies-
> kind of impossible to do with a toroid (without breaking it in half :-)
True
> The "U" core shape definitely seems easier to wind- is iron power
> available in shapes other than toroid?
Rods and slugs AFAIK.
> Is there a good reason for using the toroid?
Not for this application to my knowledge (other than to minimize
radiation). But I've used ferrite rods in chokes with no real
problems. Perhaps someone who chose that core shape could answer this.
Malcolm