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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: tiny dc/dc
Date: Sun, 6 Apr 2025 23:55:18 +1000
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On 5/04/2025 10:50 am, Klaus Kragelund wrote:
> On 30-03-2025 23:43, Uwe Bonnes wrote:
>> john larkin <jl@glen--canyon.com> wrote:
>>> Check out UCC33420.
>>>
>>> It's a tiny cheap isolated dc/dc converter. It switches at 64 MHz!
>>>
>>
>> I guess Murata NXJ switches at a similar frequency!
> 
> Wont they get in trouble with conducted emissions, since only a very 
> small parasitic capacitance from primary to secondary is able to push a 
> lot of current at 64MHz?

Not if you double screen. A conducting screen on each side of the 
isolation barrier, grounded to its local ground, blocks electrostatic 
coupling. Of course the currents flowing in the screens produce some 
voltage drop and that does drive some current across the isolation 
barrier, but a whole lot less.

Ralph Morrison's 1960 book - "Grounding a Shielding Techniques in 
Instrumentation" has quite a lot on that, not that 64MHz came into it 
back then.

-- 
Bill Sloman, Sydney