[sdiy] Power distribution board

[David G. Dixon]

Wow, great replies!  Thanks to all.

I've had a look at Ken Stone's board, and it has six parallel traces: +15V,
0V, 0V, and -15V for analog, and then +5V and 0V for digital.  If the
digital supply has its own ground, then why two grounds on the analog side?
Are these two grounds ever used separately on individual modules?  (I've
just wired mine together on the boards I've built so far.)  As the MOTM
board does not supply +5V for digital (as far as I can see), do they drop
the voltage level for digital at each module as required, and then reserve
one of the ground connections for digital?

Also, what is the standard wire gauge to use for connecting the modules to
the power distribution board?

Thanks in advance!

David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C. V6T 1Z4
Canada
 
Tel 1-604-822-3679
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> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of Roy J. Tellason
> Sent: Friday, April 03, 2009 9:53 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Power distribution board
> 
> On Saturday 04 April 2009 12:20:47 am David G. Dixon wrote:
> > I've just taken delivery of a Power-One +/-15V, 1.5A power supply, and I
> > need to etch a distribution board for it.  I would like to build
> something
> > like the MOTM board with an array of MTA156 4-pin connectors, and I'm
> > wondering if anyone can point me to a PCB image for something like that.
> > If not, I will have to draw my own, in which case I have a question:
> >
> > I ascertain that it is important to connect each ground pin to the power
> > supply ground buss with it's own trace (the so-called "star ground"
> > configuration).  Is this important enough to justify the inconvenience?
> If
> > so, then should one also do the two power rails this way?  Also, what is
> > the deal with the two ground pins on the 4-pin connectors?  Are they
> > actually different?
> >
> > Power distribution seems like a fairly important thing -- I don't want
> to
> > screw it up!
> 
> Having each and every load in whatever system it is that you're building
> having its own power run to the main distribution point and ground point
> is a
> nice idea theoretically,  but not doing so isn't going to get you in
> anywhere
> near as much trouble as ignoring this idea completely and letting things
> fall
> as they may,  convenient to routing traces and whatnot.
> 
> I personally would have no particular problems with connecting power and
> ground to a bunch of modules by way of a number of heavy buses on a board,
> though if it'll make you feel better sprinkle assorted bypass capacitors
> along it,  to deal with whatever bits of noise might end up there.
> 
> If you really want to get some idea of the effect,  figure the maximum and
> minimum current that any given load is going to present to the supply,
> then
> figure out what voltage drop these are going to create for a given
> interconnect,  whether it's that bit of distribution board trace or the
> connectors you're using (all of which have _some_ resistance) or some
> other
> aspect of things.  Having all that info on hand the calculations get a
> little
> cumbersome after a while.
> 
> I suspect that the overall noise won't amount to that much.  I also
> suspect
> that some decoupling at the power pins of each module or board will help
> this
> some as well.
> 
> There's also a fair amount of stuff I've seen that ran two sets of
> grounds.
> One instance would be a 22 gauge ground lead for something that didn't
> have
> much of a current draw,  the other would be an 18 gauge wire for stuff
> that
> did,  like audio power amps and such.  This was in organs.  Another
> instance
> of separating things out like that is when analog and digital get mixed on
> a
> board,  there will often be separate grounds which,  while ultimately both
> of
> them end up grounded the digital side will tend to have (and even
> generate)
> more noise,  which you wanted to keep out of the analog lower-level stuff.
> And the old c64 had two separate and distinct +5V supplies,  one on-board
> and
> one coming from the external power brick,  the onboard one mostly feeding
> the
> VIC and SID chips and not much else IIRC.  (Depended on what version of
> the
> board you had too.)
> 
> How important this is depends on what you're gonna use that PS for.  What
> will
> it power?
> 
> --
> Member of the toughest, meanest, deadliest, most unrelenting -- and
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> -
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