From: "Helmut Sennewald"
Subject: Re: switching dc-dc: DIY or off-the-shelf
Date: Wed, 11 Dec 2002 21:34:33 +0100
References: <firstname.lastname@example.org> <email@example.com>
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"Bob Wilson" schrieb im Newsbeitrag
> In article <firstname.lastname@example.org>, email@example.com says...
> >On Sun, 08 Dec 2002 17:17:28 GMT, Jim Thompson
> > wrote:
> >>On Sun, 8 Dec 2002 06:09:02 +0000,
> >>John Woodgate ,
> >>In Newsgroup: sci.electronics.cad,
> >>Article: ,
> >>Entitled: "Re: switching dc-dc: DIY or off-the-shelf",
> >>Wrote the following:
> >>|I read in sci.electronics.design that Winfield Hill
> >>|wrote (in ) about 'switching dc-dc: DIY or
> >>|off-the-shelf', on Sat, 7 Dec 2002:
> >>|>This can be solved by placing the inductor far away, by taking
> >>|> special care of any signal-wiring topology, or by using pot-core
> >>|> inductors. Or by all of the above. :>)
> >>|What about toroids? Do the inductor values have to be very precise,
> >>|justifying pot-cores?
> >>Pot-cores might be better due to there being a substantial DC
> >>component in the current.
> >ferrite toroids with air gap seems to be a good idea
> Sure, if you like generating emi.
> Ferrite torroids are almost NEVER used as energy storage inductor cores.
> Permalloy toroids sometimes are, but they are different because the air
> is distributed, not cut at one point. The gap cause a high amount of flux
> fringing, and basically destroys any advantage that a toroid may have.
> The most common cores used in switchmode converters are E-E cores (and
> relatives such as ETD), and the various power "pot" cores such as RM
this may be true for transformers and high power applications.
I have used in my designs mostly toroids like these, but from different
The nominal inductance in this data sheet are a bit misleading.
At full rated current, the inductance will drop to 60%..70%.
So be carefully when selecting the appropriate inductor size.
The maximum current I needed was always below 2 amperes.
> Not only are they nearly as good as a "true" toroid, they are far easier
Who will wind his own inductors? Better look for standard parts.
They cost a fraction of any custom part.
You should also look for a standard part if you need a transformer
for more voltages with a secondary DC/DC converter.
I agree with your advice of the core types for high power and
primary DC/DC converters.