[sdiy] In search of a reasonably precise comparator output

[Scott Gravenhorst]

It would be helpful if we knew what was being driven by the comparator.  Logic inputs
don't require absolute 0.000 volts for a low logic level nor absolute Vcc for a high logic
level.  Each logic type will have it's own specification for that.  Is this a zero volt
and five volt source for some analog process - or is it digital?

Guy McCusker <guy.mccusker at gmail.com> wrote:
>--===============1895041468437579696==
>
>Thank you.
>
>I can readily stick a solid 5V reference on the pull-up of an
>open-collector or open-drain comparator, but I am feeling stupid about what
>happens for the low output voltage. The LM339 data sheet lists a V_OL of
>150 to 400mV. That's a reasonable way above 0V.
>
>Should I just live with it and trim it somewhere else in the circuit?
>
>Guy.
>
>
>
>
>On Wed, 20 Jun 2018 at 17:02, Pete Hartman <pete.hartman at gmail.com> wrote:
>http://pi3c.lan/cgi/mailbody.cgi?MD4696.MSG=+Get+&MAILBOX=chordman&DATE=20_06_2018_04_00_20
>> On Wed, Jun 20, 2018 at 10:30 AM, Lloyd Abbott <lloydabbott94 at gmail.com>
>> wrote:
>>
>>> What rails do you have available ? Have you considered a comparator IC
>>> (e.g. LM339) rather than using general purpose op-amps ?
>>>
>>> If you have 0V, +5V and +15V rails, with an LM339 you can reference the
>>> comparator input side to the 0V and +15V rails and have the output side
>>> referenced to 0V and +5V. The datasheet has an example circuit using one
>>> pullup resistor and one cap per comparator.
>>>
>>>
>>
>> I was going to suggest this as well.  The 339 and its family are all open
>> collector outputs, so you can use a pull up to any voltage you like, a rail
>> or a reference voltage or whatever to get the swing you need and if
>> necessary convert levels.
>>
>

-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- http://scott.joviansynth.com/
-- When the going gets tough, the tough use the command line.
-- Matt 21:22