Re: SMPS mains circuit

From: John Woodgate (jmw_at_jmwa.demon.contraspam.yuk)
Date: 07/09/04 

Date: Fri, 9 Jul 2004 20:52:38 +0100

I read in sci.electronics.design that legg <legg@nospam.magma.ca> wrote
(in <ksote01sqlthev67vv2qc8goln9585t7kf@4ax.com>) about 'SMPS mains
circuit', on Fri, 9 Jul 2004:

>If the variations have no signifigance, then perhaps it's because
>there is already sufficient margin in the standard to cover variations
>of this sort.

That's not the point. The people involved are concerned about the
variations they observe, irrespective of whether they actually result in
non-compliance.
>
>As the standards are written in absolute current value limits, the
>assumption that worst case occurs at full load might be incorrectly
>adopted.

The problem is more significant for Class D products, where the limits
are proportional to active input power, because of the spectral
characteristics of the emissions.

We don't assume that worst-case is at full load; in fact for Class D
products, it usually isn't.

>Loading tolerances might also be signifigant as product
>inefficiencies are introduced, for economy's sake, after innitial
>certification.

That has been taken into account as well.
>
>Has the testing body or representative ever been called to task for a
>report that is unrepeatable? I doubt it.

More than one testing body is involved. The associations representing
testing bodies have been informed about the problem, as have the
assessors in at least two countries. I have no doubt that when the
analysis is complete, some 're-training' will occur where necessary.
>
>Has retesting ever produced unexplainable non-compliant results in a
>fully-functional product?

Well, not non-compliant, as far as I know, if the standard is understood
correctly (which in some cases it wasn't), but variations in measured
value of 4:1 have been observed, which is not exactly reassuring unless
the reason is fully understood. 

-- 
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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