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EMC question

Now, on a switching supply, you're supposed to have a Y-type cap between input and output commons, to shunt the RFI coupled across the transformer's interwinding capacitance (and maybe a common mode choke on input and/or output to improve that isolation with respect to the surroundings). But what should you do if the output side is also bouncing (different frequency, out of phase)?

Specifically, imagine a high side gate drive circuit powered by a DC-DC converter. The driver's "common" is bouncing at, let's say 320Vp-p, so it's not really "common" in any useful sense. What then? Should there be CM chokes anywhere, or would those only make things worse (e.g., resonating with the parasitic capacitances)?

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams
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If the dc/dc converter doesn't freak out, just let the transformer capacitance get pumped. Maybe there's no problem. Use reasonable filter caps on the input and output of the converter.

Or use a very low capacitance converter; you may have to make that yourself.

Or use a common-mode choke.

Or use my SSR-flying-capacitor dc/dc converter.

Depends.

John

Reply to
John Larkin

Newbie here.. Isn't there going to be a combo of common and differential noise line ..? If there's more common noise, then have more common mode xformer Z. If it's there's more differential noise, then have more differential xformer Z.

D from BC Amateur smps designer British Columbia, Canada Posted to sci.electronics.design

Reply to
D from BC

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