# Can you get a negative and positive voltage out of the same source?

I have recently started working with electronics. At this point, electricity still seems like magic to me, so please take it easy on me.

I'm working on a project which requires two different voltage inputs: +9 Volts and -9 Volts. I was wondering if there is a way to provide these two using the same voltage power source (In this case a 9 volt battery). I tried some things such as setting up the circuit in different ways but none of those ways worked.

I remember I had tried this like 10 days ago. I don't exactly remember the set up that I had but I was getting the readings I wanted. Now that I tried it agian and couldn't get it to work, all I can think of is that may be this is impossible. May be the first time I tried it I was using the DMM incorrectly and somehow that led to false readings in the DMM of +9 and -9 volts at the same time. Though, I remeber at some point I had two DMMs at the same time one reading +9 V and the other -9 V.
Again, I don't really know much about electronics. Let me know what you guys think.

Thanks

all I can think of is that may be this is impossible.

Well it is not impossible but I don’t think you were close.
You have to have what is called a voltage inverter, the simplest way to make this is with an oscillator and center taped transformer. Then you rectify the two half windings and smooth and regulate.

May be the first time I tried it I was using the DMM incorrectly and somehow that led to false readings in the DMM of +9 and -9 volts at the same time.

Yes I would put money on you fooling yourself.

Depends on your requirements, but a charge pump can be used to make a negative supply. Not that a lot of power is available from it, but a MAX232, which runs from +5, has a "-10V" available.

What is your application? if you need +9V and -9V for say an op-amp you can get a 9 volt center tap transformer and a couple of diodes and capacitors to do the trick.

If this doesn't make sense to you and you are completely green, you may have to back track and learn a little basic electronics to get very far with your project.

You could also just use -2- 9 volt batteries connected in series, with the center-point tap becoming your reference ground; the positive of battery 1 becomes +9 volts, and the negative of battery 2 becomes -9 volts...

Often on the net it is knowing the right words to search on. In this case the words are voltage mirror

What about the MAX680 ? That might work, has long the application load is “very” light.

The datasheet : http://www.hvwtech.com/products_view.asp?ProductID=1107

ImNotPedro:
I'm working on a project which requires two different voltage inputs: +9 Volts and -9 Volts. I was wondering if there is a way to provide these two using the same voltage power source (In this case a 9 volt battery).

What do you need the -9v for? It may be possible to redesign the circuit without it, e.g. if it is providing the negative supply to an op-amp then you may be able to use a single rail op-amp instead.

If you can't redesign the circuit to avoid the need for a negative supply, then a charge pump will give you around -7v to -8v if the current requirement is only a few mA. If you need more than that, use a DC-DC converter, or a second 9v battery.

there are several forms to do it, this one is very simple way
Check the diagram

Double power.pdf (213 KB)

But the OP, who seems to have diasapeare said in the first post

In this case a 9 volt battery

So that circuit is not going to do much from a battery. Read my first reply.

Yes there is and it's very simple. You need a couple of regulators, lm7809 and lm7909, and a voltage source that is higher then the drop out of the regulators. The dropout voltage of the 7809 and 7909 is about 2 volts. So you need at least 11 volts but more is better up to a point. Extra power is released as heat and the max these regulators will go is 35 volts. Here is a link to a thread I posted showing how this is done:

The circuit in the above thread is minimal. You should consider looking at the data sheet and it will show you how put caps in the circuit.

Yes there is and it’s very simple.

I think you misunderstand that circuit. The OP is asking to get +9V and -9V from a 9V battery. At best that circuit can only give you + / - 4.5V from a 9V battery. It is a rail splitter.

If that circuit actually worked as posted, not the experiment you did, you would get 30V out of a 24V battery which is clearly nonsense.

Grumpy_Mike:
If that circuit actually worked as posted, not the experiment you did, you would get 30V out of a 24V battery which is clearly nonsense.

Unless the circuit was a boost converter

You can search for "dc dc converter" on Digi-Key, and come up with a large number of chips and regulators that can do this. Typically, they are called "inverting regulators" or "inverting converters." Also, typically, they will use an inductor and a capacitor and a Schottky diode to get where they need to go, in addition to the inverting boost controller/regulator itself.
The good news is that these count as "switching" regulators, and thus can be fairly efficient. Darlington-based ones like the MC34063 aren't terribly efficient (80% or so,) but MOSFET based ones with really low Rdson and very low drop-out Schottkys can be > 90% efficient, if that matters. Also, a low-frequency switching converter (50 - 100 kHz) will run fine on a breadboard without oscillation; a 1 MHz converter likely needs very careful attention to the circuit layout. So go for the low-frequency ones!

Unless the circuit was a boost converter

You might have noticed that the circuit I am referring to is not a boost converter.
It is rather like me saying, you are never going to go 200 miles per hour on a peddle bicycle and you saying your are if you strap rocket boosters to it. True but totally irrelevant.

Grumpy_Mike:
It is rather like me saying, you are never going to go 200 miles per hour on a peddle bicycle and you saying your are if you strap rocket boosters to it. True but totally irrelevant.

I was referring to this part of your statement, which I quoted:

you would get 30V out of a 24V battery which is clearly nonsense

You are saying that "Getting 30V out of a 24V battery is clearly nonsense," without qualifying the statement, and using this as an argument for why the circuit is not going to work.
Getting 30V out of a 24V battery is not "clearly nonsense," because you can do this if you use a boost converter. While I understand what you mean with your sentence, someone who does not know the difference between linear regulators and switching regulators will not, because the argument is incomplete. The way it was written, it could be read to mean that there is no way to step up battery voltage.

Assuming that the goal is to share how to do things better, I went on to describe exactly how to achieve what the OP wants to achieve, in this context, with sufficient theory to at least cover the "what" (not necessarily the "why" or "how.")

Now we can all play the bloody minded pennant, but I am better at it than most if you want to take me on.

You are saying that "Getting 30V out of a 24V battery is clearly nonsense," without qualifying the statement,

But you see I did qualify the statement, the whole of that quote reads:-

If that circuit actually worked as posted, not the experiment you did, you would get 30V out of a 24V battery which is clearly nonsense.

So the qualification I made was "If that circuit actually worked as posted"
Now oddly enough, that actually means the circuit as posted. If you look at this you will see that each of the "regulators" are labeled 7819T and 7519T.

So unless you can come up with an isolated DC / DC converter that will work with out any external components AND is called 7819T and 7519T then you are wrong as there is no way it can be a boosting converter. Therefore making my statement true.

However if you can supply a link to two boosting regulators that are capable of working in that configuration and that have that as the part numbers or part of the part numbers, then I will post an apology for not being completely accurate.

Grumpy_Mike:
Now we can all play the bloody minded pennant, but I am better at it than most if you want to take me on.

Not at all interested. My goal is to make sure that the point is clearly communicated to those who may not have all the facts. I think your statement didn't, and I think mine did. I don't know whether you disagree or not, because you're discussing something else.

I don't know whether you disagree or not,

I do disagree with you.

because you're discussing something else.

No I am not.