[sdiy] Logic to +/-5V conversion

Tom Wiltshire tom at electricdruid.net
Sun Nov 22 21:45:48 CET 2015


Nope, I don't think you're missing anything. 311 comparator would be a reasonable solution, and if you've got one in the circuit already, that makes life simple.

On 22 Nov 2015, at 20:16, Tim Ressel <timr at circuitabbey.com> wrote:

> So here I am laying out the 4053 solution when it occurs to me that I can run all the logic on +/- 5V. I have LM311 comparators turning analog into digital but those can do +/- 5V outputs as well. That should give me my bipolar outputs without having to massage the levels.
> 
> Or am I missing something?
> 
> --TimR
> 
> On 11/21/2015 1:14 PM, rsdio at audiobanshee.com wrote:
>> 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.
>> 
>> Brian
>> 
>>> 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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> 
> -- 
> --Tim Ressel
> Circuit Abbey
> timr at circuitabbey.com
> 
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