[sdiy] Source for good power supply schematics

[Roy J. Tellason]

On Saturday 28 May 2005 03:05 pm, Seb Francis wrote:
> Hi,
>
> You will find 2 here:
> http://www.elby-designs.com/asm-1/psu/psu-about.htm
>
> If you are only running a small application then you will probably find
> the "Low-cost" one good enough.  It is +/-15V .. to make it +/-12V just
> use 7812 & 7912 instead of 7815 & 7915, and lower the transformer
> voltage accordingly.

I don't see a need for separate "analog ground" and "digital ground" pins on 
the outputs of these,  anything digital I'm likely to be doing is going to be 
run off its own +5v supply anyhow (with rare exceptions).  I also see where 
this page calls the current capabilities out as 100mA at one point,  250mA 
elsewhere -- those regulators can handle in excess of 1A,  if properly 
heatsinked and the input voltage is reasonably low,  unless you're using one 
of the lower-current variants of these parts.

> The more complexe LM723 design can also be changed from +/-15V to +/-12V
> very easily - just by changing 2 resistor values (and use a lower
> voltage transformer of course).  See the LM723 datasheet for more info.

I see where he's using two 723 chips.  It's quite possible to do a dual supply 
with a single 723 and an op amp,  and it also has the benefit that the 
outputs will track each other.  I can't remember where exactly it was I saw 
this but it was in either Popular Electronics or Radio Electronics somewhere 
around 1971 or 1972.  The single biggest advantage I can see to going with a 
723 is if you need oddball voltages,  precision voltage selection,  pick your 
own current limit values (or have it be adjustable),  or similar stuff.  The 
page author mentions lower noise,  but it's also my understanding that the 
317 / 337 regulators are significantly better than the 78xx/79xx parts in 
this regard.

The magazine article I'm remembering had a design using just the 723 that was 
good to 150mA,  one with a 2N4918 boost transistor that was good to 500mA,  
and one using a 2N3055 in addition to those that was good to a couple of 
amps.

I have some 723 chips,  and doubt very much that I'll ever be bothered doing 
anything with them,  unless I end up needing a real precision lab-type supply 
for some reason,  and I don't anticipate that happening any time soon.

> Jesse Yoder wrote:
> >I am looking for good schematics for DC power supplies, one regulated
> >at +/- 12V and one regulated at +/- 15V.  I had to design power
> >supplies in electronics class in college, but that was a long time ago
> >and I really don't remember much of anything,
> >
> >Thanks,
> >~~Ponyboy