Negative voltage from positive power supply: how does it work? - Page 1
Forum section: electronics / beginners

author: augustol
author_rank: Contributor
timestamp: July 30, 2021, 05:44:43 pm
content: So, I've been looking around and seeing a lot of resources about getting a negative voltage from a dual output power supply. Some of them from very reliable sources like BK Precision.So, it got me thinking: hooking up a positive voltage to the ground of the other output sounds to me like a short. I know it isn't since I trust this sources and I've actually seen people doing it on youtube and stuff, but how does it work? Is there a special kind of circuit inside to make it possible? Or the sources are separate from each other all the way?I'm going to build myself in a near future a power supply from a pre made supply. It will be a single 24v 10A power source which I intend to get two switching regulators so that I can get two positive variable outputs. Would I be able to do this with this simple power supply of mine?Just as a note: I do intend to have a negative supply, but I'm going to do it with a negative regulator. This is more of an academic interest.

author: esepecesito
author_rank: Regular Contributor
timestamp: July 30, 2021, 05:59:27 pm
content: If the positive your are hooking to ground comes from another independent source, there is no short circuit. Think of it as 2 series batteries.The answer to your question is, I guess: "they are separated all the way."You will be able to do it, as long as the two supplies do not share the ground.

author: TimFox
author_rank: Super Contributor
timestamp: July 30, 2021, 08:22:32 pm
content: Most, but not all, dual power supplies contain two isolated voltage supplies, to allow series connection or grounding one negative and one positive output to get a split supply. They also usually have a front-panel terminal connected to the chassis and protective-ground in the line cord to facilitate that connection. As esepecesito stated, think of them as two separate batteries.Some dual supplies are designed to "track", where one knob controls both supplies together, and there is probably a connection between them, since typically one supply is connected to produce the negative of the other supply.

author: Zero999
author_rank: Super Contributor
timestamp: July 31, 2021, 04:56:08 pm
content: Another thing to note is the 0V node of a circuit is the point, from where all voltages are measured from. Two 9V batteries in series are normally used to make a -9V to 0V to +9V power supply, if the voltages are measured relative to the point where the batteries are connected, but exactly the same circuit can be 0V +9V and +18V, or 0V -9V and -18V, depending on where the voltage. i.e. the 0V node isCredit to Brumby for the above schematic:https://www.eevblog.com/forum/beginners/negative-voltage-70656/msg977146/#msg977146

author: David Hess
author_rank: Super Contributor
timestamp: July 31, 2021, 09:04:51 pm
content: Quote from: augustol on July 30, 2021, 05:44:43 pmConnecting the positive output to ground requires that the supply be galvanically isolated or floating. Advantages include not requiring a negative regulator design. One disadvantage is that a tracking regulator implementation is more difficult.