[sdiy] In search of a reasonably precise comparator output
ben.pi.bradley at gmail.com
Wed Jun 20 20:24:57 CEST 2018
Run the output through a CMOS buffer/inverter powered by the exact 0V
and 5V power supply. If this is to drive something with less than
megohms of resistance. add an op-amp unity gain buffer.
If that's "too simple" or for some reason doesn't work, use a 4066 or
other analog switch power from -2 and +7V to switch the exact 0V and
On Wed, Jun 20, 2018 at 12:46 PM, Ben Bradley <ben.pi.bradley at gmail.com> wrote:
> Run the output through a CMOS buffer/inverter powered by the exact 0V
> and 5V power supply. If this is to drive something with less than
> megohms of resistance. add an op-amp unity gain buffer.
> On Wed, Jun 20, 2018 at 12:09 PM, Guy McCusker <guy.mccusker at gmail.com> wrote:
>> 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?
>> On Wed, 20 Jun 2018 at 17:02, Pete Hartman <pete.hartman at gmail.com> wrote:
>>> On Wed, Jun 20, 2018 at 10:30 AM, Lloyd Abbott <lloydabbott94 at gmail.com>
>>>> 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.
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