[sdiy] More ground questions

Ingo Debus debus at cityweb.de
Sun Aug 4 18:03:09 CEST 2002


harry wrote:
 > Hi Ingo...
 >
 > I either don't understand (or don't agree with..) you.
 >
 > If the grounds are separate... AC currents from dirty signals bypassed
 > to the dirty ground... MUST flow in the dirty ground all the way 
back to
 > the common ground point.
 >
 > This is presumably the lowest impedance point of the power supply 
system...
 >
 > These currents do not flow in the clean ground, ever... so they 
cannot cause
 > voltage drops and therfore noise in the clean ground.
 >
 > I'm also presuming that the positive and negative power supply 
leads are separate
 > as well.

Yes, if there are separate supply lines for dirty and clean circuitry,
then separate ground lines make sense.

But in the original mail "four pin connector cables" were mentioned,
as I understand it, one for clean ground, one for dirty ground, one
for positive and one for negative supply. No separate dirty and clean
supply lines.

If there are bypass caps across both the dirty and the clean loads
these two caps (in series, with the supply line in the middle) will
short both ground lines together.

Ingo






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