# How to get negative voltage out of 5V DC adaptor??

#### zero_coke

Joined Apr 22, 2009
294
I have two adaptors that are 5V DC output, but I need one to be +5V DC and the other -5V DC...is there anyway to convert the other one into negative 5Volts?

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#### jimkeith

Joined Oct 26, 2011
540
Why not swap the leads at the barrel connector?
If you want it to look nice, there are connectors available at Radio Shack.
Make sure you mark everything clearly so they do not get accidentally swapped...

#### Wendy

Joined Mar 24, 2008
23,475
Several ways. You need to make a square wave generator, then feed it into a voltage doubler, where it will come out around -8V give or take, then regulate.

You can also use the SMPS method, which is similar but uses inductor kickback.

#### t06afre

Joined May 11, 2009
5,934
Negative voltage is just that you "reference" point is more positive than your measuring point. Just take a battery and measure the voltage. Then swap around the measurement probes. And the polarity will change. Take two 9 volt batteries and connect the poles as marked. By using this as the reference point (COM/GND). You will be measuring +9 volt on the rightmost pole and -9 volt on the leftmost pole

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#### zero_coke

Joined Apr 22, 2009
294
t06afre: I have 2 adaptors as in adaptors you plug into the wall. Its output is +5V DC and I believe one is ground and the other is +5. I was wondering how to change one to -5V DC and I know how to do it with batteries but I don't know how to do it with an adaptor that only has ground and +5V DC output...

And Bill: I don't know what you mean. I don't have a square wave generator or anything. Is there any IC chip I can feed in +5V DC and get -5V DC?

#### bountyhunter

Joined Sep 7, 2009
2,512
t06afre: I have 2 adaptors as in adaptors you plug into the wall. Its output is +5V DC and I believe one is ground and the other is +5. I was wondering how to change one to -5V DC
They are fully floating. You can tie the + side of one of the 5V outputs to ground and that automatically makes the other terminal -5V. It's called 'stacking" with the center node tied to ground.

#### zero_coke

Joined Apr 22, 2009
294
So ok, let me clarify this for myself: Each adaptor I have has 2 outputs: one is +5V and other is GND (ground). So what you're saying is:

Adaptor 1: Keep +5V, and keep GND
Adaptor 2: Connect +5V to some other ground, and GND will become -5V??

#### JoeJester

Joined Apr 26, 2005
4,390
Measure the Ground to the AC return plus on the wall wart. If the result is zero ohms ... then they are not fully floating.

#### t06afre

Joined May 11, 2009
5,934
So ok, let me clarify this for myself: Each adaptor I have has 2 outputs: one is +5V and other is GND (ground). So what you're saying is:

Adaptor 1: Keep +5V, and keep GND
Adaptor 2: Connect +5V to some other ground, and GND will become -5V??
Yes that is corret. Just connect what you call GND on adaptor 1, to +5 on adaptor 2. This will be the new GND in your system. The ground on adaptor 2 will become -5 volt