Re: [SI-LIST] : EMI due to fans

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Thu Oct 12 2000 - 10:01:13 PDT


Are DC fans collector-type ? Then you have sparks, and so you are bound to have
some EMI.

Sunil Kumar wrote:

> Patrick.
>
> Yes, DC fans are being used. I have already tried that. I had powered up
> fans from separate power supply. But still I did see increase in jitter.
>
> Sunil
>
> On Thu, 12 Oct 2000, Patrick Lawler wrote:
>
> > If a DC fan is being used, the pulsating current load current may be
> > feeding back through the power supply into the logic circuitry.
> > This applies whether the fan is brush or brushless.
> >
> > If this is your situation, try powering the fan from a separate power
> > supply to see if the symptom goes away.
> >
> >
> > On Thu, 12 Oct 2000 11:41:55 +0500 (GMT+0500), Sunil Kumar
> > <sunilb@cdotb.ernet.in> wrote:
> > >I am measuring cycle-to-cycle jitter in clock in a system, where clock
> > >(PECL, 50MHz) is going from one PCB (card) to other through twinax
> > >cable. In the second card clock is converted into TTL and then distributed
> > >to various ICs. I am looking at the clock just before the PECL-to-TTL
> > >convertor. Both the cards are in the same backplane. The system is
> > >equiped with a set of fans for cooling, which are kept below the card
> > >frame. Now what I have observed is, when the fans are not on, jitter is
> > >much much less in comparision of the jitter when fans are on. I think, the
> > >fans are generating EMI, which is disturbing the planes in the backplane
> > >and the cards, and hence jitter is increased. Any explanations?
> > >
> > >One more thing which I have observed is, the PECL-to-PECL clock
> > >fanout buffer (no PLL inside) is reducing jiiter (with fans off), i.e.
> > >jitter at input is more than that at output. Can anybody explain this?
> > >
> > >Is there any PECL-to-TTL clock fanout buffer which adds very low
> > >jitter? The PECL-to-TTL buffer which I am using, is adding lot's of
> > >jitter.
> >
> >
>
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