[sdiy] Logic to +/-5V conversion

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sat Nov 21 22:14:50 CET 2015

On Nov 21, 2015, at 5:58 AM, Simon Brouwer <simon at brousant.nl> wrote:
> Opamps in general are not the best choice for this unless you select a rail to rail output type (assuming you have -5 and +5 rails).
Agreed, with a couple of caveats regarding my original response.

First, I assumed that +/-12V is available (Doepfer modular), so +/-5V would not be an issue at all for a standard op-amps.

Second, I somehow missed that Tim only wants to output +5V and -5V exactly, and not anything in between! For binary output, an op-amp is a bit overkill, although it will provide the proper voltage to just about any load.

> I would use LM339 which is a low cost quad comparator. It has open collector output though, so you need pull-up resistors.
Good suggestion, but the pull-up voltage will sag when high currents are sinked by the load. When the output is -5V, though, the voltage will be consistent under any normal load.

I tried to come up with a simple, two-transister FET solution with a complementary pair of depletion-mode PFET and NFET transistors, but it looks like the task requires three or more transistors to work.


> Best regards
> Simon
> > Op 21 november 2015 om 2:49 schreef rsdio at audiobanshee.com:
> > Doing it with op amps IS the clever way. But I think that pulling it off with a single op-amp, as opposed to a dual, is the cleverer way. I recently worked this out for +/-10V, but I can't find the paper where I scribbled down the notes.
> > 
> > There's a DAC data sheet out there with the 0-5V to +/-5V op-amp circuit in it as an example of interfacing their DAC. Forgot who that was, but sounds like you already have that circuit.
> > 
> > Brian
> > 
> > 
> > On Nov 20, 2015, at 4:51 PM, Tim Ressel <timr at circuitabbey.com> wrote:
> > > Hi y'all,
> > > 
> > > I'd like to take several 0-5V digital lines and make them swing +/-5V. I can do it with op amps, but is there a clevererer way?

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