[sdiy] +-12V supply

[Roy J. Tellason]

On Wednesday 12 January 2005 07:57 pm, Pat Kammerer wrote:
> Okay I'm making a PCB for an improved power supply (based on 7812 and 7912
> TO-220), and I had a quick question.
>
> Other than larger filter capacitors, are there any simple modifications to
> the "basic" regulated power supply which would enable even lower noise
> floor?  Maybe it's too vague, but I'm not sure how else to put it.  I just
> want to make a good simple low noise linear PSU.

For that sort of a supply,  I'll generally put some smaller caps across the 
big ones.  Say,  a 1-10 uF tantalum part,  and also a 1-10nF ceramic part.  
Also a "spark eater" cap across the primary of the transformer,  if that's 
do-able,  as long as you use one that has appropriate safety ratings.  And a 
couple of those smaller caps across the outputs of the regulators as well.

Then to protect the regulators,  I put diodes from the output to ground and 
from output to input -- just make sure that the way you put them in ensures 
that they're reverse-biased in normal operation!  :-)  Any diode will do,  
more or less,  and I tend to use either low PIV rectifiers (1N4001 and such) 
or 1N914 or whatever.

Depending on your wiring,  you might also want to repeat those smallish caps 
on the board(s) where the load is,  too.

Typical datasheets for those regulators will mention that cap at the output,  
and will say something like a 1 uF tantalum or a 25 uF (!) electrolytic.