# Generating a negative voltage from a +24V DC source?

1. Feb 20, 2010

### ephedyn

I have a standard AC-DC rectifier that gives me +24V, 12.5A power supply. Now, I've a problem... what's the simplest way to generate a negative voltage between the rails?

This may sound silly but I really thought I could just use the power supply as I would do to generate a positive voltage, but just run an extra wire to ground the end with the higher potential. Maybe I'm misunderstanding how the power supply works because it clearly didn't work.

I ran a search on "generating negative voltage" and saw a number of solutions involving ICs. But these have been proving quite expensive. I found it simple to invert the voltage, but maintaining a 12.5A output will be a problem. Will be great if someone can recommend me a solution! Thanks.

2. Feb 20, 2010

### dlgoff

You'll need a center tapped transformer to get a split supply.

3. Feb 20, 2010

### vk6kro

Do you want to:

Have a negative supply instead of the positive one?

Have a Positive and a negative supply, both 24 volts at 12.5 amps? (but not 12.5 amps from each at the same time)?

Have your 24 volts become plus 12 and minus 12? ie a split supply with a ground in the middle?

Have an additional negative voltage as well as the plus 24 volts, but the negative supply can be at low current?

4. Feb 20, 2010

### Bob S

Last edited by a moderator: May 4, 2017
5. Feb 21, 2010

### ephedyn

^dlgoff: I'll preferably not build another power supply =/ But thanks nonetheless for letting me know about the center-tapped transformer... I'll use that someday if I need a low-noise application.

^vk6kro: I'll like to have the first one: a negative supply instead of the positive one. My supply actually gives me 3 x 24V rails and 3 x 0V rails. I was thinking of something along what Bob S suggested - using a inverting circuit based on a DC-DC converter after one of the 24V rails.

It will be much easier for my application if I can get a higher current than 2A though; do you have an idea for that?

^Bob S: Cool, you always have something close to what I need. The -12V/2A output topology seems good... I think I'll use that if there's no other alternative.

What do you think of this LM22677? http://www.national.com/pf/LM/LM22677.html#Overview [Broken] I have it to produce 12V/5A... any idea how to get it to -12V/5A?

Thanks everyone!

Last edited by a moderator: May 4, 2017
6. Feb 21, 2010

### ephedyn

Oh wait, problem solved! I was referring to the wrong page of http://cds.linear.com/docs/Datasheet/3758f.pdf [Broken]

Much thanks for everyone's input!

Last edited by a moderator: May 4, 2017