From: John Devereux
Subject: Re: Magnetically Shielded Inductors
Date: Fri, 27 Sep 2002 08:39:33 +0100
NNTP-Posting-Date: Fri, 27 Sep 2002 07:38:21 +0000 (UTC)
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"Bill Sloman" wrote:
>"John Devereux" wrote in message
>> Which have lower magnetic emissions, unshielded toroidal or
>> "shielded" bobbin core inductors?
>> I am looking at inductors for a 500kHz buck SMPS and want to
>> minimize the local magnetic interference.
>> For example,
>Toroids should be better. A toroidal coil has no external magnetic field,
>even if you leave out the toroidal core.
Really? I didn't know that, not what I would have guessed.
> Real toroidal coils are rarely
>perfectly uniform toroids so there is usually some external magnetic field,
Especially with the miniature ones I have been looking at, I
>but not a lot.
>Theoretically, a pot core is topologically equivalent to a toroid and should
>have the same zero emission, but real pot cores have slots to allow
>connections from the coils inside the pot core to the outside world, and
>these slots do allow some leakage flux - more than you get from a toroid.
>The cylindrical coil in a pot core is a lot easier to wind than a toroid,
>which is why the "shielded" bobbin core inductors are so much more popular.