Re: [SI-LIST] : Power Supply---get a clean +/-5V from PCI slot of PC?

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From: Mike Saunders (mikesa@ia.nsc.com)
Date: Thu Jun 01 2000 - 10:24:32 PDT


Shengli,

The first thing is to ensure you have adequate decoupling, both bulk and
high-speed. The critical areas are at the switching regulator, at the
connector and at the op-amp.

The second recommendation I would make, if decoupling is not enough, is
using an "analog filter" type design, where the power is actually brought
through a ferrite bead (or inductor) to an isolated plane or fat trace.
Make sure to decouple the "new" voltage as well. If absolute isolation is
required, try doing the same for the ground rail with another ferrite bead,
but this usually isn't required except for extremely sensitive circuits.
This analog filtering can be used for your 12v rail, the 5v rail or both.
If decoupling a negative voltage, be sure to maintain correct polarity on
your caps.

The third recommendation is to comb through your design and look for
aggressor signals which are routed too close to any other part of your
power or op-amp circuit. Also look for points of noise injection to your
power supply, ie- from fast-switching ICs.

Hope some of this helps.

--Mike

At 05:36 PM 6/1/2000 +0800, you wrote:
>Dear experts,
>The commercial PC use switch power supply module, and the power
>supply +/-12V in the PCI slots is not clean enough for our OP Amp
>use, I try to get a clean,low ripple,stable +/-5V from that +/-12V,
>using LM317,LM337, I am afraid it's not enough...
>Can any experts suggest me how to further process the +/-12V(+/-5V) and
>get a nice +/-5V on my PCI card?
>Your respones is greatly appreciated.
>
>Have a nice day!
>
>
>
>Shengli Liu
>Fast Electronics Lab
>Univ. of Sci. & Tech. of China
>
>
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