Power Supply Question

[Anigavevoli]

I'm working on a build that requires a dual 9V power supply.  I purchased this from futurlec.....
http://www.futurlec.com/Mini_Power_Dual_12V.shtml
....and picked a +9V regulator and a -9V regulator.
I want to hook these up correctly the first time, so I took a look at the datasheets and I saw this:

It looks pretty cut and dry, except for the area circled in red.  Should this be connected to the mini board's ground, or not?  If not, where does it connect?

Thanks,
Martin

[head_spaz]

What? You no can lead Engrish?
This is probably the result of improper translation from Chinese into English.
Usually that symbol is used for Earth-Ground, commonly refered to as Chassis-Ground,
where the ground connection of your AC house wiring is connected to the chassis to
prevent the hazards of electrical shock in case of internal electrical failure.
(in case your transformer melts down and shorts household AC where it doesn't belong.)

That connection in the red circle goes to your transformer's center-tap of the secondary
winding, which becomes your DC ground reference. As per safety regulations, it is also
connected to chassis ground, but sometimes this connection will lead to excessive audio
noise and hum in sensitive audio circuits, so some DIY's ignore the safety guidelines and
allow the DC Ground to float. If your transformer is a wallwart, chances are you can skip
the chassis connection.

I would suggest that you add another general purpose diode, reverse biased, across each
regulator's input and output terminals to prevent destruction of the regulators when the
power is shut-off, and any capacitors beyond the regulators attempt to discharge backwards
thru the regulators. They don't like that. This is not always necessary, depending on the circuit,
but it is common practice to provide the extra protection.

Like this...



Good luck with your project, and welcome to DIYstompboxes.

[Anigavevoli]

First of all, thanks for the quick reply!

I realize that in a typical application, the regulators would be connected to a transformer.  This situation is a bit atypical because of the fact that I already have a regulated +/- 12V supply from the mini board.  The 12V regulators will be connected to the transformer, and I will already have +12V, -12V, and DC ground connections.  What I'm trying to do is to regulate the 12V supply down again to 9V.  If my thinking is correct, it would look something like this:

But with the addition of the reverse biased diodes you mentioned.

In which case, I'll just be connecting the ground of the first stage of (12V) regulators to the ground of the second stage of (9V) regulators.  This looks right?

Thanks again,
Martin

[head_spaz]

Sounds like a plan. But I would still ground it right at the center tap, to avoid ground loops.
Good luck and let us know how it works out for you.