Need a comparator but don't have one?

[cjdelphi]

I've only ever built this once, but it did the job....

 

[PETERDECO]

Use an opamp without feedback resistor

 

[cjdelphi]

Use an opamp without feedback resistor

what do you think the circuit I created does?

it is the fundamental basics of an opamp

 

[Harald Kapp]

Use an opamp without feedback resistor

Works, but is usually rather slow compared to a comparator.

 

[WHONOES]

I have used opamp's as comparators. They usually require a bit of hysteresis via positive feedback to work correctly otherwise they can have a tendency to oscillate at the point of transition. As for speed that depends on the device used. But, yes proper comparators are preferable and easier to implement.

 

[Alec_t]

If the comparator switching threshold isn't critical you can just use a single Schmitt trigger gate, e.g. CD40106, with its input resistively biased above/below the inherent threshold as required.

 

[danadak]

One drawback of CD40106 type of logic parts is they have a very low
trip accuracy for a specific valued voltage, eg. no good Vref to compare
against. As well as wide sensitivity to supply V and Temperature. You can
get comparators today with onchip Vref to solve that issue.


Regards, Dana.