Derek,
Most of the PS manufacturers I've dealt with use passive
dummy loads or "quiet" active loads. These very handy
quiet active loads provide programmable loading, BUT IN NO
WAY SIMULATE THE SUPPLY'S ACTUAL USE. In other words, how
many quiet loads do you power? Almost every load is a
micro or some digital electronics.
I've been training my clients to inject heavy noise at
their load outputs [common mode and differential mode] to
make certain that their supplies are not "transparent" to
those variable loads. Most now test some time during
development with active digital loads to make certain their
supplies don't pass the noise right back through the
supply.
Above 30MHz does not require a lot of bulk for filtering.
Most of the bulk is there for the near 150KHz noise.
You'll find that part selection and layout are more
critical for filtering above 20MHz.
I always encourage end-users to include "operating" specs
in their PS purchase agreements to put the burden for
proper design back onto the PS manufacturers.
- Robert -
Robert A. Macy, PE [email protected]
408 286 3985 fx 408 297 9121
AJM International Electronics Consultants
101 E San Fernando, Suite 402
San Jose, CA 95112
On Wed, 2 Jul 2003 15:16:22 EDT
[email protected] wrote:
> Hi All,
>
>
> Thanks for the great replies!
>
> looks like the PCI bus is the problem.. But here's the
> quandry..
>
> Now we are adding the cards back in, they should add
> little to the profile,
> correct? After all, they all have the CE mark on them,
> and some have the FCC
> sticker too.
>
> This is not happening, in fact some emissions are quire
> strong.. I've also
> noticed that the Power supply is letting the PC noise
> out. I opened the power
> supply ( bang goes the warrenty ), and there is the
> minimal of filters.. Are the
> power supplies tested individually to carry the agency
> sticker?, with a real
> PC? or just load resistors? Are they designed to suppress
> the PC noise?
>
> Cheers,
>
> Derek N. Walton
> Owner L F Research EMC Design and Test Facility
> Poplar Grove,
> Illinois, USA
> www.lfresearch.com
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