Split Supply

grrr_arrghh · Apr 28, 2004

Hi.

If I want to power a project such as **broken link removed** using a single battery or a single power supply, how do I generate a split supply? (without changing any of the circuit, although I wouldn't mind adding extra curcuitry).

Thanks for any help.

Tim.

andrew2022 · Apr 28, 2004

easiest was would be to get a second battery. if you do, connect the positive and negative of 1 battery to the other. this is your common, the positive from 1 battery is your 12v (assuming the batt is 12 v) and the negative from the other battery is the -12v

gerty · Apr 28, 2004

Andrew..I believe you mean connect the pos of one battery to the neg of the second, that would but the batteries in series and that tie point would be 0 with the the other terminals being +12 and -12..

andrew2022 · Apr 28, 2004

gerty said:
Andrew..I believe you mean connect the pos of one battery to the neg of the second, that would but the batteries in series and that tie point would be 0 with the the other terminals being +12 and -12..

thats what i ment... just worded it badly...

grrr_arrghh · Apr 28, 2004

andrew2022 said:
easiest was would be to get a second battery

Thats what I wanted to avoid. Any way of just using one battery? Might voltage regulators or something work?

Nigel Goodwin · Apr 28, 2004

grrr_arrghh said:
andrew2022 said:

easiest was would be to get a second battery

Click to expand...

Thats what I wanted to avoid. Any way of just using one battery? Might voltage regulators or something work?

The circuit shown runs off +/-15V, you could very easily run it off a single supply of 30V - generating the split supply with a couple of resistors and a capacitor.

Perhaps you had better mention what you are wanting to run it off?.

grrr_arrghh · Apr 29, 2004

Nigel Goodwin said:
Perhaps you had better mention what you are wanting to run it off?.

err well, it wasn't for a particular project, but I do quite alot of things with op-amps, and i'm just trying to do some general research to fill gaps in my knowledge.

Say my supply is a regulated linear power supply, something like 12v (DC), max current of, say, 500mA (the sort of supply I would use by choice)

Does this narrow it down at all?

Nigel Goodwin said:
generating the split supply with a couple of resistors and a capacitor

I hadn't though of using double the voltage required, then splitting it, although I haven't seen many mains adapters that can supply 30Vdc...?

Thanks

Tim

Roff · Apr 29, 2004

See this thread.

Nigel Goodwin · Apr 29, 2004

As this isn't for any specific circuit, using the 12V supply simply split that and run the opamps off +/-6V. As you would be designing the circuit knowing what the power supply is it wouldn't be a problem.

I built a simple two channel mixer many years ago for a disco I had to do suddenly, it only took about half an hour, I powered it off a single 9V battery and split that to give +/-4.5V - it worked perfectly :lol:

grrr_arrghh · Apr 29, 2004

thanks Ron H, and Nigel.

I'm still a bit confused, how do I get the negative supply?

The way i see it, I can get +9v, +4.5v and 0v (ground) - when using a 9v battery or PSU. Where do I get the negative from...?

Thanks again

Tim

Sebi · Apr 29, 2004

The solution...

Roff · Apr 29, 2004

As I said in this thread, I think you would be better off with a ground buffer. See schematic below.

Sebi · Apr 29, 2004

Yes, of course, Ron's circuit better, because the divider resistors suck only 45uA, and the virtual GND more stable. (but also need the two capacitors)

Nigel Goodwin · Apr 29, 2004

Ron H said:
As I said in this thread, I think you would be better off with a ground buffer. See schematic below.

Yes, it's certainly better - but it may not be needed, depending on what it's feeding. If you have a spare opamp left over, fair enough - otherwise adding an extra opamp takes more space and money. The big advantage of the buffer is that it will cope with differing current requirements on the positive and negative rails - a simple resistor splitter doesn't cope very well.

grrr_arrghh · May 1, 2004

hi

Thanks to everyone

As Nigel says, the op-amp takes space and money, I think I'll stick to the simpler version.

Sebi, thanks for drawing the diagram, but I still don't quite get the ground bit. The way I see it - ground is 0v, which is the negative terminal on the battery (?), so in effect the 0v output and the -4.5v outputs are connected together...? Maybe I've got something wrong.

Thanks

Tim

Nigel Goodwin · May 1, 2004

grrr_arrghh said:
hi

Thanks to everyone

As Nigel says, the op-amp takes space and money, I think I'll stick to the simpler version.

Sebi, thanks for drawing the diagram, but I still don't quite get the ground bit. The way I see it - ground is 0v, which is the negative terminal on the battery (?), so in effect the 0v output and the -4.5v outputs are connected together...? Maybe I've got something wrong.

No, you don't make any other connections to the battery except those shown - the negative terminal of the battery is no longer 0V, it's now -4.5V. It's probably a hard concept to get round, but all voltages are relative - 0V, +ve, -ve - they are all relative to something.

For a single battery, you would normally measure relative to the negative connection, and call that 0V - everything else is measured relative to that point (and would be positive voltages). There's nothing to stop you measuring from the positive connection, and calling that 0V - in that case all voltages would be negative. It's just normal practice to measure from the negative of the battery for a single supply - it wasn't always the case, very old transistor circuits were germanium PNP, and commonly used +ve as the 0V reference point.

For a split supply (as used for opamps etc.) the 0V reference is commonly the half way point, so you get both positive and negative voltages.

grrr_arrghh · May 2, 2004

Nigel Goodwin said:
It's probably a hard concept to get round,

Actually, it makes alot of sense to me, its just that GCSE Electronics corses have a habit of not telling you the whole story, or in some cases just lying blindly.

Last quick question, if I wanted to ground (for example) the casing, I would connect that to the '0v'?

Thanks very much everyone.

Tim

Nigel Goodwin · May 2, 2004

grrr_arrghh said:
Actually, it makes alot of sense to me, its just that GCSE Electronics corses have a habit of not telling you the whole story, or in some cases just lying blindly.

My daughters just had a GCSE Music revision book (she's only year 8, but has been playing for the year 11 exam recordings), in the book it says "bass guitars only have four strings, and you NEVER play chords". I bought her a new five string bass guitar on saturday, and she also plays chords on it sometimes - in particular playing Placebo tunes.

In general Electronics is very badly taught in UK schools, it's unusual to get a teacher who knows anything about it

Last quick question, if I wanted to ground (for example) the casing, I would connect that to the '0v'?

Yes you do!.

grrr_arrghh · May 3, 2004

Nigel said:
"bass guitars only have four strings, and you NEVER play chords".

lol, I like it :lol: . bass guitars play loads of chords, especially in jazz..., and I know quite a few people with 5 and 6 string bass(es)...How are these people alowed to write these books?!? Its simply irresponsible!!

anyway, thanks very much for all your help.

Tim.

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