# Split supply

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#### stef10

##### New Member
Hey guys, in a circuit im trying to establish a 12V, -12V voltage sources. I have an op-amp which requires it.

My teacher gave me a hint that if you had a regular 12V voltage supply it was possible in a way to use virtual grounds and voltage dividing with resistors and an op-amp to achieve this although I dont see exactly how. Hopefully you have some answers.

Thanks.

#### Hero999

##### Banned
You won't be able to get +/- 12V from a 12VDC supply using a virtual ground, you'll get +/-6V.

If depends on the circuit, post a schematic.

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#### Hero999

##### Banned
That's a viertual ground, how about the rest of the circuit?

#### MikeMl

##### Well-Known Member
That puts a virtual ground half way between 0V and 12V, effectively splitting the world so you have -6V and +6V relative to the virtual ground, NOT -12V and +12V.

And because your teacher used power-wasting 100Ω resistors to create the voltage divider, he/she obviously lacks real world experience.

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#### stef10

##### New Member
well, he only gave me this as a hint and said I could from this supply the op-amp with 12V, -12V

#### crutschow

##### Well-Known Member
well, he only gave me this as a hint and said I could from this supply the op-amp with 12V, -12V
He is in error. With a single 12V supply, you can only generate ±6V using a virtual ground.

#### stef10

##### New Member
so I need a 24V source, thats just great.

#### Hero999

##### Banned
It'll probably run from +/-6V otherwise he wouldn't have suggested that.

We can't help you because you haven't posted the schematic for the circuit you want to power.

#### stef10

##### New Member
its mainly this circuit, does it really need +12V and -12V or can we just use 6V?

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What is IC2a/b?

it is an op-amp

#### MikeMl

##### Well-Known Member
it is an op-amp
What opamp. I was going to look up the specs on its data sheet (which is what you should do, if you did you would not have posted your question)

#### stef10

##### New Member
I was more questioning it the 12V was for another part of the circuit and not for the op-amp. But at first I need to consult with my teacher because im not sure if we have these kinds of op-amps.

Thanks for the help, I will post again if I have a question my teacher might have messed up

#### Hero999

##### Banned
It's important to know what type of op-amp is used so you know it'll work down to +/-6V.

You just connect the ground symbol on the second circuit to the output (pin 3) of the op-amp in the first circuit.

R1 and R2 on the first circuit should be increased to save power (try 10k) and a 100nF capacitor should be connected across either of them.

You should use a quad op-amp if possible to save money and space.

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