[sdiy] Power distribution board

[Roy J. Tellason]

On Saturday 04 April 2009 01:30:00 pm David G. Dixon wrote:
> This leads to my next question:  Presuming that most have only +/-15V
> supplies in their modulars, what is the best way to handle digital power?
> I've only breadboarded circuits with TTL chips powered by a 7805 reducing
> +15V to +5, and was startled (and a little frightened) at how hot the
> regulator ran.  I'm not sure I'd want anything that hot on any of my
> lovingly hand-crafted boards!

That's also fairly wasteful of power...

Commercial gear that I've seen that uses those kinds of levels typically seems 
to use a separate winding on the transformer (though for homebrew stuff I'd 
see a separate transformer as being easier to find with suitable outputs) and 
rectifier / filter circuit so what's going into any regulators isn't all that 
high.

> I was thinking I would probably opt for just putting the +15V through a
> simple voltage divider to get +5V and be done with it, but I'm wondering:
> is this anathema?  Does one find oneself excommunicated from the fold for
> such heresy?

Dropping 10V for a 5V output is wasting twice as much power in the regulator 
as the load is using,  which is truly horrible from an efficiency standpoint.

I hear that there are chips that make switching regulators real easy these 
days,  too.

> > -----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: Saturday, April 04, 2009 10:14 AM
> > To: synth-diy at dropmix.xs4all.nl
> > Subject: Re: [sdiy] Power distribution board
> >
> > On Saturday 04 April 2009 05:50:29 am Julian wrote:
> > > Somthing ive wondered -
> > >
> > > Regulators are cheap - what about a power bus running over-voltage and
> > > then a pair of dedicated regulators for each and every socket on that
> > > bus? 
> > >
> > > Would that effectivly isolate every module?
> > >
> > > (im thinking back to my old doepfer lfos thatlld modulate the doepfer
> > > vcos on the same bus...)
> >
> > That was the approach taken for the real early S-100 bus computer
> > systems, with the power buses being 8V, and +/-16V,  which were typically
> > regulated down to 5V and 12V on each board.  Some boards had to have
> > multiple regulators for the 5V,  and there were heat dissipation issues. 
> > Later systems put jumpers in place of the regulators and used switching
> > power supplies instead,  though I've not much experience with them.
> >
> > But yeah,  I'd say this would provide a lot of isolation.



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