Re: RF choke ferrite materials

To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: RF choke ferrite materials
From: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz>
Date: Thu, 4 May 2000 08:57:06 +1200
In-reply-to: <4.1.20000502074837.009e4180-at-pop.dnvr.uswest-dot-net>
Organization: Massey University at Wellington, NZ
Priority: normal
Reply-to: malcolm.watts-at-wnp.ac.nz

Hi Marco,
                A very interesting question:


> Original Poster: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi> 
> 
> Hello all.
> 
> Recently Mike Hammer posted on the Tesla-2 list an interesting address:
> 
> http://www.bytemark-dot-com/amidon/
> 
> It seems like they have in stock large ferrite toroids, at a feasible price ($
> 10 - 15) and no minimum order. This is a rare case, in my experience.
> 
> Now my questions, about building a couple of protection chokes to be connected
> between the tank and the primary circuit.
> 
> What kind of ferrite material should be selected? An iron-powder (mu about 10)
> to avoid saturation at high currents or a wide-frequency ferrite with a higher
> mu?

The iron powder cores have a distributed airgap in them. This 
enables them to handle a high level of DC. However, the greater the 
AC  component, the greater their losses. They heat very quickly with 
high ripple currents in SMPS applications. So if it's low Q chokes 
you want, they are a good bet but expect a lot of heating. I think I 
would try them with tough insulated wire dunked in oil or something 
like that.

Regards,
Malcolm

References:

RF choke ferrite materials

From: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)