Comparator referenced to ground?

Thread Starter

MikeJacobs

Joined Dec 7, 2019
95
So trying to work with a comparator referenced to ground.

have people found this to be difficult in general?

I imagine unless the op amp used internally to the comparator IC is a rail to rail op amp this could be an issue?
Any thoughts?
 

OBW0549

Joined Mar 2, 2015
3,203
So trying to work with a comparator referenced to ground.
Okay...
have people found this to be difficult in general?
No.

There are plenty of comparator ICs whose input common mode range includes ground (or their negative supply terminal). Three of them are the LM393 dual comparator, its quad version the LM339, and the LT1116.

A visit to the website of any of the major IC manufacturers will yield many more. Browse through their offerings, read the data sheets, and pick the best one for your job.
 

Thread Starter

MikeJacobs

Joined Dec 7, 2019
95
So can you help teach me a what to look for in the data sheet that tells me I can ref it to ground
I’m still a bit hazy on all
The CM stuff
What should I be looking for as a spec that allows a ref of gnd?
 

OBW0549

Joined Mar 2, 2015
3,203
So can you help teach me a what to look for in the data sheet that tells me I can ref it to ground
I’m still a bit hazy on all
The CM stuff
What should I be looking for as a spec that allows a ref of gnd?
Well, for the LM393 for example, it's right there on the first page, under Features: "Input Common-mode Voltage Range Includes Ground."
 

Thread Starter

MikeJacobs

Joined Dec 7, 2019
95
Well, for the LM393 for example, it's right there on the first page, under Features: "Input Common-mode Voltage Range Includes Ground."
Yea I saw that
Nice and easy on that one
I was looking for something that possibly had a latch feature
I had made a post about that in a different thread but don’t want the threads to overlap. Sorry about that
 

Audioguru again

Joined Oct 21, 2019
858
A LM393 or LM339 inverting comparator will not work if its input reference is ground and it does not have a negative supply, unless you follow its maximum allowed input voltage limit of -0.3V.

If the comparator is inverting then with the non-invereting input reference at ground, the inverting input must go negative below ground to cause the output to go high. Do you have an input signal that you limited to only -0.3V?

If the comparator is non-inverting then with the inverting input reference at ground, the non-inverting input might need to go negative below ground to cause the output to go low due to input offset voltage.
 

OBW0549

Joined Mar 2, 2015
3,203
That is what I suspected
Is it even possible to have a ref of ground on a single supply comparator?
Of course it is, provided your circuit does not try to force the non-grounded input more negative than -0.3 volts.

So is it possible? Yes. Does it make sense? Probably not; whatever you're trying to achieve, there's probably a better way to do it than a single-supply comparator with one input grounded.
 
Top