DC-DC Converter Reverse Polarity?

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digi001

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Hi I am making a PCB that has power coming into the board as 12V and 5V.

However I also need a on-board -12V power rail for some OpAmps. If I use a 12Vto12V isolated DC-DC Brick, then connect it up backwards so that output 12V is ground and output GND is 12V, would this give me the -12V that I need?

What is a better way to do this?
 

See the isolated converter output side as a 12V-battery, does it work?

A better way (cheaper, higher efficieny) is an inverting buck-boost converter.
 
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    digi001

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FvM said:
See the isolated converter output side as a 12V-battery, does it work?
Click to expand...

I see your point as a Battery. Its just a floating voltage, so Yes. Thanks.

FvM said:
A better way (cheaper, higher efficieny) is an inverting buck-boost converter
Click to expand...

Thanks for this suggestion. So I would need to pick out an IC Controller and build a inverting buck-boost? This would be non-isolated, but inverting? Wouldn't this take up more real-estate than a DC-DC brick? Isn't a DC-DC brick just a compact completed solution of a buck-boost or maybe flyback if isolated?
 

How much current do you need?
If it is only a few mA, you could do it with a charge pump IC like the ICL7660
 
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    digi001

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Depending on how good it has to be, you might be able to
take a capacitor coupled feed off the switching node, and
two more diodes plus another cap gives you a charge pump.
You'll have those diodes' offset of course, but most op amps
don't care a whole lot about common mode offset (the effect
of asymmetric power supplies) or you might even be improving
the common mode position if your input common mode is
above ground.
 
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    digi001

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