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Toroidal Transformer Screening

Hi

Another magnetics question!

I have a SMPS which uses a toroidal ferrite transformer. It switches at ~100kHz, works very well, it's not my design and I can't change it.

However, it introduces noise at about 50kHz onto/into my electronics which causes a problem. After much experimentation, I found that putting an earthed screen around the transformer kills the problem quite dramatically. The screen must be earthed, and doesn't need to be magnetic.

This is something I can do. I don't have much room but I guess that wrapping copper tape around its exposed enamelled wire will cause problems for Edward Current. Is there a rule of thumb for what sort of gap to leave between the windings and a screen? How quickly does the field drop off?

(And yes, I know not to make a shorted turn.)

Cheers

--
Syd
Reply to
Syd Rumpo
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It seems that you have capacitive coupling. You can probably use aluminum foil, if that is convenient. Any metal should work.

If you have control over the assembly's layout, it would be wise to arrange things to nip it at the source.

Reply to
John S

The toroid will see your shield only if the mu is quite low. I don't know how low it would need to be, but you seem to be doing some good experimenting, so watch your results as you apply the shield at various distances.

Consider such things as copper-clad kapton tape, or, for test purposes, you can get metalized tapes from the hobby stores.

Reply to
John S

On Fri, 17 Jul 2015 09:59:24 -0500, John S Gave us:

Home depot Copper roof flashing by the roll.

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or amazon makes these, which are quite a bit cheaper than a 20' roll.

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Or better still a variety pack from ebay:

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Reply to
DecadentLinuxUserNumeroUno

OK, i will bite: what is Edward Current? and where do i get a description? The quacker DuckDuckGo fails.

Reply to
Robert Baer

He is using the formal name rather than the nickname (Eddie).

Reply to
John S

Oops! Should be Eddy.

Reply to
John S

I thought it was rather clever!

Reply to
Tim Watts

Well, I haven't met the guy, so it seems a bit forward to use his diminutive.

Cheers

--
Syd
Reply to
Syd Rumpo

Thanks for your input, I'll try the tape.

Cheers

--
Syd
Reply to
Syd Rumpo

Me, too. I wish I had thought of it. In fact, I did and from now own it's mine.

Reply to
John S

Thanks. Kissing cousin of Mister Justin Case..

Reply to
Robert Baer

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