Generating negative rail from isolated supply

Thread Starter

Gibson486

Joined Jul 20, 2012
355
I am generating a negative rail. The positive rail is a non isolated dc switcher powered from the original supply. The negative rail is an isolated dc to dc module (powered from the original supply), but with the output polarity switched. It seems to work, but i am getting push back from others. Does this need to be done with two isolated supplies, or is one isolated supply good enough?
 

MrChips

Joined Oct 2, 2009
30,706
1676558405570.png

As shown in your drawing, the +V supply has its negative terminal connected to GND.
The -V supply has its positive terminal connected to GND.
If you ensure that this is correct then you are good to go.
Usually, this means that at least the -V supply must be floating.
 

Thread Starter

Gibson486

Joined Jul 20, 2012
355
View attachment 287677

As shown in your drawing, the +V supply has its negative terminal connected to GND.
The -V supply has its positive terminal connected to GND.
If you ensure that this is correct then you are good to go.
Usually, this means that at least the -V supply must be floating.
Thanks!

I thought it would work, but this had me doubting myself....

I did not work yesterday (my initial PS was just over currenting....), so I was prepared to do some hours of debugging this morning. However, when I powered it up this morning (just let everything sit overnight on the lab bench), it worked and everything was powered and happy. So odd....
 

MisterBill2

Joined Jan 23, 2018
18,167
I have used 2 ADEQUATELY ISOLATED DC to DC supplies exactly in that sort of scheme, but attempting it with supplies that are not adequately isolated will result in damaging overloads at best, and possibly destruction of the connected equipment at worst.
 

LowQCab

Joined Nov 6, 2012
4,023
Depending upon all the various details of the whole Circuit ..........

If the non-isolated Regulator/Supply doesn't create any problems with the Circuit operation,
then there won't be any problems,
( Ground-Loops, Noise, Short-Circuits, etc. ),
regardless of the addition of additional isolated Regulators/Supplies.

An additional, completely isolated, Regulator/Supply will not create any additional problems that
were not already there, and just waiting to happen, in the first place.

An Isolated-Power-Supply can be thought of as a Battery with some level of Electrical-Noise added in.
A non-isolated Power-Supply could possibly be a "Bucket of Worms".
.
.
.
 
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