Using 2 postive regulators with 2 prong power supplies for bipolor power supply

Question

My nephew and I have been working on a circuit that uses +/- 4.5V. Up until now we have been using 2 3-AAA battery holders to supply each leg and now wish to move to mains power.

My question is, discounting the more unusual topographies(auto transformers, cap dividers), is it safe to assume that 2 2-prong 5V(12V) power supplies are isolated from each, and therefore I can use 2 positive regulators to regulate the output. As noted in some of the comments, I have metered inside/outside of the barrel to each prong, with all of them showing open.

I know I can use 2 separate taps from a transformer for this.

In the past I've used 2 supplies like this in a audio application(sans regulators), and it worked fine.

If it comes down to it, I can dig out a multi-tap transformer(not a center-tap) and use that, but that's a lot of work, and the result is much heavier, hotter and less efficient compared to using 2 wall-warts.

And as far as I know, using an inverted buck DC/DC still requires a negative regulator.

Answer 1

If you view the output of a black box that has two wires coming out from a power source inside, one ++ and the other -- you would never know if it was a negative or positive regulator. In addition any current flowing out the ++ has to flow back in the -- wire when a load is connected between the two. All just depends on what you bring out as GND.

So as long as the wall warts that you use have:

1. 100% isolation between the input AC terminals and the DC outputs
2. No connections to the AC side safety GND

You can use the two wall warts along side each other, one as the +V supply and the other as the -V supply. Just tie the opposite sides of each together to become the DC circuit GND.