# Bipolar output from DAC with unipolar supplies

I want to use a unipolar 12-bit DAC (MCP4725) as a function generator with bipolar output (from -2.5 to +2.5V). Problem is, I only have two supplies of +5V and +12V referenced to the same ground, so most opamp based solutions go out the window since I am unable to give a negative power supply to the opamp. I need to get a bipolar output from this circuit, where the 'ground' (reference) of the circuit using this bipolar output is the same as the ground of the power supplies.

I have given this some thought and arrived at a conclusion that logically it would not be possible to get bipolar output from unipolar output. However, the wise people here have proven me wrong earlier and I wanted to try my luck.

TL;DR: Get bipolar output from unipolar DAC, only positive power supplies, same ground everywhere.

There are now opamps with on-board charge pumps that give bipolar outputs from a single positive supply.

See the update in this answer for details.

Use a small DC to DC converter to generate a negative power rail is my advice: -

Of course you can design your own using a fly back transformer: -

The one above produces + and - 12V from an input that covers the range 8V to 36V. The trick here is to recognize that both secondaries are isolated so you can cross wire them how you want.

• Yes, that is an option I have considered however unable to implement it due to other constraints... looking for some weird ideas here that would never occur to me. thanks though. Feb 25, 2016 at 18:02
• So basically you've wasted my time and want a weird solution. Feb 25, 2016 at 18:03
• I'm sorry you feel so but I simply meant that I will be unable to make a DC-DC converter in my circuit, and am looking for options more along the lines of what peter smith answered. Feb 27, 2016 at 13:07

While this might not be true AC operation, at least in the sense that your output goes negative with respect to ground, you could do a sort of pseudo AC by AC coupling the DAC through a capacitor to the output.