re 7905 connections -

> Do you have it correctly connected? The centre leg is NOT the ground leg.
> Don't ask how I know - but it was learnt many years ago. :)))))

Knowing WHY these things are so can be helpful:

(Almost) all 3 terminal regulators have the most negative part of the
circuit connected to the tag and the centre electrode. This is due to the
fact that the most negative part of the die is the substrate and this is
electrically and mechanically and thermally connected to the mounting frame.

Therefore, on positive regulators the middle tag is ground as this is most
negative in that case.

AND

on negative regulators the middle leg is Vin as this is the most negative
potential in that case.


(It is possible to build regulators differently but in most cases this is
the easiest and cheapest and most effective way to do it so that's how it's
usually done.)



            Russell McMahon

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.