How to get -12V from a 12V supply?

Discussion in 'General Electronics Chat' started by tpny, May 23, 2012.

May 6, 2012
216
0
Hi, I have a 12Vdc supply into my circuit, I want to convert that to +/-12V to power my op amp. What components, methods do you recommend I use to accomplish this? Thank you so much!!

2. ajm113 Member

Feb 19, 2011
174
5
555 Negative Voltage Generator

Worked like a charm for my hearing aid circuit.

You can also accomplish this using two power sources such as two 9v batteries or any other, without using a 555.

Last edited: May 23, 2012
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3. lightingman Senior Member

Apr 19, 2007
374
22
Check out the ICL7660.

4. #12 Expert

Nov 30, 2010
18,076
9,691
Be careful about the 12 volt limit on the chip.

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May 6, 2012
216
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1. Looks like both responses involve something to do with an oscillator.. But what is the theory behind the oscillator making negative voltage from positive...

2. What about a transformer? Does that work? What are the pros and cons of doing it with a transformer vs an integrated component?

6. #12 Expert

Nov 30, 2010
18,076
9,691
Transformers don't work on DC.

You have to turn the DC back into AC to get anything to work, and the IC's are cheaper than an IC plus a transformer.

May 6, 2012
216
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8. #12 Expert

Nov 30, 2010
18,076
9,691
"Fully encapsulated with torroidal magnetics"

That means oscillator, transformer, rectifier.

May 6, 2012
216
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how to choose: using dc-to-dc converter or using ic?

10. Sparky49 Well-Known Member

Jul 16, 2011
822
421
Just remember that voltage, or potential difference, is just that. A difference.

Imagine you have three supply rails. One at 24V, one at 12V, and the other at 3V. If you measured the voltage across the 24V and the 12V, you'd get a reading of 12V. Likewise, measure between 24V and 3V, you get 21V.

It's all about what your using as your ground reference point. If you use the 3V rail as your 'ground', and measure against the 12V rail, you're going to get a reading of +9V. Makes sense, seeing as how 12 is 9 higher than your 'ground' point.

However, if you take the 12V as your ground, and measure the 3V, you'll find that you get a reading of -9V. Makes sense, seeing as to get to 3, you have to add -9V.

This is why you see the oscillators. They are just change the 'ground point', form which you can take your 'negative' voltage.

11. Slik_Willie New Member

Mar 14, 2010
5
0
Since the 555 timer output is limited to 200 mA (source/sink) I guess that this circuit can drive only really small loads. Any solutions for currents in the 1A neighborhood?

May 6, 2012
216
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Ok, I get the concept of relative voltage difference.. but why ocsillate? And in doing so achieving a constant -12V?

13. PaulEE Member

Dec 23, 2011
423
32
The circuit blob on the bottom right hand side of the 555 timer is a voltage multiplier (http://en.wikipedia.org/wiki/Voltage_doubler). They operate on AC and not DC. The 555 is just a means of pulsing the current to generate the alternating current. The orientation of the diodes and capacitors, by the nature of the circuit, results in a negative voltage WITH RESPECT TO the circuit ground. Looky here (two related nifty things):
http://en.wikipedia.org/wiki/Cockcroft–Walton_generator
http://en.wikipedia.org/wiki/Voltage_doubler

By the way, if your op-amp circuit doesn't use much current, you can use a MAX232 ( a chip for a completely different purpose, but usually in everyone's parts drawer ) to get a low-current dual-supply. This chip uses similar switching techniques as well...hence the external capacitors.