[sdiy] voltage regulator insulation

ASSI Stromeko at nexgo.de
Sun Jul 15 20:53:48 CEST 2012


On Sunday 15 July 2012, 20:02:22, ToAd wrote:
> I use an LM317 and LM337. I want to use the metal case as heatsink.
> Now I read somewhere that you need to put an insulation plate between
> the metal case and the LM's. Is this really needed?

Yes, absolutely.  The LM317 has the output voltage on the tab and the LM337 
the input voltage.  You don't want to short these two, I suppose.

> What about the bolt that I'll use to hold the LM's?

Must of course also be isolated wrt the LM3xx or the case.

> And where do I get this insulation plate? What kind of material is it?

The same place where you get the regulators, usually.  These used to be made 
from mica, but these days you can get plastic ones that conduct heat quite a 
bit better.

> And a related question, which ground do I connect the case with? Do I
> use the DC ground or the mains ground.

I sincerely hope you aren't using any mains voltages anywhere because your 
questions indicate you wouldn't be able to handle them safely.  So on the 
assumption that you use some fully-isolated external transformer, the case 
should be connected to the DC ground directly at the rectifier.  If you 
insist on putting mains into your case, have the whole thing checked by a 
professional electrician before it is plugged in for the first time.


Regards,
Achim.
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