[sdiy] Regulator / PS question

[Harry Bissell Jr]

Hi Tim
  
  yes... hallucinating.  
  
  It is the 78xx / 79xx series. The middle pin in each case is tied to the
  tab. do NOT repeat NOT trust the heatsink compound as an insulator...
  that is what the mica pad is for. 
  
  The 78xx has GROUND for the middle tab.  You might want to connect that
  directly to the sink, or maybe not.
  
  The 79xx has 'another' voltage (input, ot output ???) on the tab. Insulate that
  for sure.
  
  Sometimes... grounding the tab of the 78xx will make more than one  ground point in a cabinet and a 'ground loop' could occur. Watch out  for that !!!
  
  H^) harry

Tim Parkhurst <tim.parkhurst at gmail.com> wrote:  Hi All,

I'm working on some documents, and I'm trying to find a little info
about using 78xx and 79xx voltage regulators. I seem to recall finding
out at some point that you can't attach a 78xx and a 79xx to a common
heat sink, because the heat sink tabs on the TO-220 packages are NOT
at the same potential. HOWEVER, I can't find anything to confirm/deny
this. I seem to recall having to use insulating hardware (a plastic
sleeve) AND MAKING SURE there was a coat of silicone grease between
the regs and the heat sink when attaching a 79xx to the same heat sink
as a 78xx regulator (silicone heat sink goo is thermally conductive
but NOT electrically conductive). A mica insulator would do the same
trick I guess. If this is true, I would think that the same cautions
would apply when attaching a regulator and/or heat sink to a synth
cabinet!

Am I halucinating here? Am I thinking of some other regulator family?
Does anybody have documentation showing which pin attaches to the heat
sink tab on the 78xx and 79xx? Why do birds suddenly appear every time
you are near? Are we there yet?


Tim (the caffeine is kicking in now) Servo
--
"Imagination is more important than knowledge." - Albert Einstein


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20060302/8a670d90/attachment.htm>