G9 - Why the 78s12 must be electrically isolated ?

Jazzy_Pidjay · Sep 13, 2005

Hi everybody!

the question is in the title

the central pin of the 78s12 go to the ground
so why it's important to isolate it electrically ?

i think the central pin of the 78s12 can replace
the Pin1 of the XLR input, to put all the G9 0v to the Chassis ?

why it's not a good idea ? if it's not good ?

:? thanks

CJ · Sep 13, 2005

Si vous avez plus d'un repérage sur un radiateur, il peut y avoir ennui, puisque le métal sur un pourrait être à un potentiel différent que le métal sur des 7912 par exemple, où le métal me repose à -12 volts croyez. Vous avez que garniture intéressante de transfert d'insulator/heat de toute façon, ainsi pourquoi ne pas ajouter la rondelle d'épaule et ne pas obtenir à certains le sommeil la nuit?

Jazzy_Pidjay · Sep 13, 2005

in fact, i have isolated the TIP121 and the TL783C
so only the 78S12 is non isolated and touch the chassis

when i use the 78S12 without the mica, it's really
a lot colder than with the mica, and is the principal reason
of my question ?!

So, there's no real problem if the 78s12 is the only
regulator non isolated ?

thanks for your french answer :thumb:

:green:

gyraf · Sep 14, 2005

Yes, the 78S12 really needs to be isolated from chassis/gnd/0V - even though it's at same 0V potential. If lest un-isolated, you will get a very unpredictable grounding path, and there's almost certainly hum problems connected with this.

When you use mica insulation washers, make sure to use thermally conducting compund as well - otherwise you inhibit the heat transfer seriously.

Jakob E.

Jazzy_Pidjay · Sep 14, 2005

ok thank you very much Jakob !

it's alright

Mailliw · Sep 17, 2005

Hi,

I blindly followed a parts-list for the semiconductor components

I ordered a 2SD1275AP (2SD1275A-ND) from digikey and not the TIP121.

Specs are the same except its rated for 2A, not 5A.

Should be ok?

Thanks

gyraf · Sep 18, 2005

Should be ok. But check the pin-out!!

G9 - Why the 78s12 must be electrically isolated ?

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