# Split Rail Power Supply

Discussion in 'Power Electronics' started by Supercap2F, Mar 26, 2014.

1. ### Supercap2F

550
150
Mar 22, 2014
Hi everyone!

I need a circuit for a split rail power supply that can work with a wide range of voltages (like 3V-32V). What I do not want is 2 batteries hooked up so that the – and + poles are connected to make 0V.

Thanks

Dan

2. ### shumifan50

582
58
Jan 16, 2014
Have you tried googling split rail power supply circuits. There are millions on the web.

3. ### Supercap2F

550
150
Mar 22, 2014
Yes I did a search on the internet but I could not find any that I liked. So I thought that I would ask on the forum and see if anybody had any good ones they like to use.

Dan

4. ### Arouse1973Adam

5,164
1,087
Dec 18, 2013
What do you mean ones you liked. That means you have a preference then? Which is what? Current and voltage output? You say work with which usually means take in at the input. Or do you mean a variable output from 3V-32V.
Adam

Last edited: Mar 26, 2014
5. ### Supercap2F

550
150
Mar 22, 2014
Well the ones on the internet dropped the input voltage by about 1/2. I need about 1 amp
of output current. I would like to have one with a input voltage and output voltage of about 3V-32V if possible (not variable just able to put that range on input voltage in to it).

Thanks

6. ### Arouse1973Adam

5,164
1,087
Dec 18, 2013
I don't quite follow what you mean. Are you saying if you put in 3V you want +/- 3V out and if you put in 12 volts you want +/- 12V out and again at 32V and what with no loss at 1Amp?
Adam

7. ### Supercap2F

550
150
Mar 22, 2014
Yes thats what I mean except I want 0V out to and 1 amp output.

8. ### gorgon

603
24
Jun 6, 2011
Ok, so what you want is a general power that generates an equal negative voltage of the one you put in as positive?

I suppose you understand that if you draw a +/- 1A on the outputs, the load on the supply power will be >2A, depending on the efficiency of the inverter.

Last edited: Mar 26, 2014
9. ### Supercap2F

550
150
Mar 22, 2014
I don't know if you understand. What I want is a circuit that I can put -3V and +3V in and get -3V,+3V, and 0V out.

All the best

Dan

10. ### davennModerator

13,902
1,971
Sep 5, 2009
no, what you want is what people have been trying to explain to you...
A power supply that can be adjusted from near ~ +1, 0V, -1 to ~ +32, 0V,-32

maybe due to inexperience you are just not explaining yourself very well
You have stated you want it to "work over a wide range of voltages" your words

we all have been explaining how to do that

The input voltage needs to be a bit higher than the highest output voltage so it will need an input voltage of ~ 35V that can be regulated down and made adjustable to the other voltage outputs required

there are a lot of commercial PSU's that can do that

cheers
Dave

Last edited: Mar 26, 2014
11. ### davennModerator

13,902
1,971
Sep 5, 2009
here's an idea circuit for you

goes from 1.2V to 30V with a max of 1.5 A

being mains supplied and knowing your age and lack of experience, you need to have considerable hands on help from an experienced electronics technician

cheers
Dave

12. ### Supercap2F

550
150
Mar 22, 2014
Sorry about that I guess I misunderstood I will try to keep more open-minded The circuit you supplied works with 120VAC I feel comfortable working with voltages lower than 35VAC. So I will look into a PSU. But do you know of any circuits that use a 9V battery and take it down to a 5V split rail? Is that possible or does the input to it need to be higher?

Thanks

Dan

13. ### gorgon

603
24
Jun 6, 2011
What you are saying is that you want to put in 6V and get +3V, 0V, and -3V.
+3 - -3V = 6V.

0V will be the midpoint between +3V and -3V.

14. ### davennModerator

13,902
1,971
Sep 5, 2009
it needs to be higher 5 + 5 = 10 well it did when I went to school and then as I commented on before you need a couple of volts more than that to counter what is "lost" in the regulator operation

Dave

15. ### gorgon

603
24
Jun 6, 2011
Everything is possible, but if you want to increase the available voltage, you need to use some form of DC-DC converter. This always comes with a cost, increased power required.

In general you may have some problems with an artificial 0v from a single voltage. Due to the requirement of a symmetrical load from the input powers 2 lines, you need some form of regulator to distribute this load, if the bipolar load is asymmetrical. If you load the positive side with 1A and the negative side with 0.1A, there will be a problem.

There is areason why it is normal to use 2 batteries in series with the 0V in the connection point.

Last edited: Mar 27, 2014
16. ### shumifan50

582
58
Jan 16, 2014
I think we still suffer from lack of problem definition:
1. The 35V you are prepared to work with, is at AC or DC and what is the source, transformer or batteries.
2. Must the unit automatically adjust the outputs when you change the input voltage or can it be manually adjusted?
3. Must the outputs always be symmetrical?
4. Why do you need 1A? That requirement makes it more difficult. Several single chip solutions exist up to 120ma. So is it possible to reduce this requirement?
5.Can you live with a complex circuit (SMPS) or does it have to be simple.
6. What level of accuracy is required, overall and per rail?

From what I understand the following link solves your problem for -15V, 0V, +15V at 1A.
Dual rail PS from 12V/24V DC max output current 1A with adjustable output voltage up to -15V/+15V

Last edited: Mar 27, 2014
17. ### Supercap2F

550
150
Mar 22, 2014
1. It's DC and up to 12 volts I would be using batteries 12 volts and greater I would be using a transformer
2. either way will work
3. I guess I don't understand what you mean
4. It needs to have at least 1 amp for any relays or motors in the circuits I might build.
5. As long as I can assemble it and use it it's ok
6. I guess I don't understand what you mean here either

The circuit you supplied uses SMD components which I do not think I could solder.

Thanks guys

Dan

18. ### shumifan50

582
58
Jan 16, 2014
3. Symmetrical= (-3,0,+3) vs assymmetrical (-5, 0, +12)
4. What I mean is how accurate must the voltage be; within 0.1V or 0.5V and how much ripple can you put up with. How important is the exact rail to rail split(can it be off some amount).

If you are using a transformer, then get a transformer with a centre tap and you will find many circuits on the web to create what you are after. The problem comes when you want to supply a single input voltage.

19. ### Supercap2F

550
150
Mar 22, 2014
3. Yes it needs to be symmetrical
6. It can be off about is much as a 7805 is. But 0.1V off would be nice

Thanks
Dan

20. ### KrisBlueNZSadly passed away in 2015

8,393
1,271
Nov 28, 2011
Are you after a supply voltage splitter with 1A output capability?

This would be a circuit that you connect to a DC power source, say between 6V and 35V, and it will provide a "half way between" output that becomes your 0V rail, while the positive and negative connections from your input source become symmetrical positive and negative rails, equal voltages above and below the 0V rail.

Have a look at the results from this search: https://www.google.com/search?q=high+current+supply+splitter+-phase&tbm=isch

There's also an article at http://www.edn.com/design/consumer/4428197/3/Simple-PS-voltage-splitters-based-on-audio-amplifiers that explains them.

If that's the kind of thing you want, and you want to be able to draw up to 1A from either side at the output, it needs to be based on a power amplifier, with a low output impedance. The output transistors will need to be heatsinked, especially if you will be running it at more than around 12V input voltage.

Is this what you want? Are you prepared to build up a circuit with an IC, several transistors, a heatsink, and assorted resistors and capacitors?

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