positive / negative power supply from two separate units?

Thread Starter

unprovoked

Joined Apr 2, 2009
2
I would like to power a circuit with an op-amp (acting as voltage to current converter) and two transistors (acting as current amplifier) with +12V and -12V. The output current can be as high as 3A. So, I need a dual power supply +12/3A and -12/3A.

Can I use two table-top power supplies (Jameco #220442; regulated switching), and reverse the leads on one of them? A previous post stated something relevant, but I don't completely understand:
"This does not apply to non-isolated DC power supplies where one terminal is hardwired to a power common, (or neutral) connection and you are not free to swap polarities simply reversing connections to your application."
How do I know if the table-top supply I'm interested in has a "terminal hardwired to power common"? It's datasheet says:
2.5. 2-wire input AC line (Line Neutral)
3.11. The DC ground will be isolated from the AC neutral and AC line

I am not an engineer, so please try to explain in the simplest terms possible.

Thank you!
 

beenthere

Joined Apr 20, 2004
15,819
The statement -
3.11. The DC ground will be isolated from the AC neutral and AC line
- tells you that the output is not hardwired to the AC wiring. You can stack the supplies to get your +/- 12 VDC.
 

KL7AJ

Joined Nov 4, 2008
2,225
I can't speak specifically to your supply, but most lab quality supplies have floating outputs, where you can tie either end to ground...or another supply. I imagine yours would work fine.

eric
 

KL7AJ

Joined Nov 4, 2008
2,225
By the way, if you want a really cool project to work on, you can build a tracking regulator...it's a bipolar supply that always keeps the ground at precisely the midpoint. Great way to learn about op amps~

Eric
 

Thread Starter

unprovoked

Joined Apr 2, 2009
2
Thanks for the incredibly fast responses and also for the link to mpja.com (which is so much cheaper).

For other similar supplies, if I can't find a spec sheet, how can I tell if DC ground is isolated or not? For example, how do you know if http://www.mpja.com/prodinfo.asp?number=17261+PS or http://www.mpja.com/prodinfo.asp?number=16918+PS is isolated and thus the leads reversible?

Out of curiousity, what would happen if the DC ground was not isolated and someone tried to reverse the leads?
 
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