Hello everyone

I have a question about rail-to-rail comparator and I am not sure if this is the right forum

anyway

can anyone tell me what is rail-to-rail comparator and what its difference from the normal comparator?

Should I use LM311 to obtained rail-to-rail comparator or one can get this type with any other integrated circuit

and what is the physical meaning of the term (rail-to-rail)?

thank you in advance

 

"Rail-to-rail" is a term relating to operational amplifiers and comparators to indicate that the input common-mode range includes both the (+) and (-) supply rails and all voltages in between. As you can see from the LM311 data sheet, it does not have rail-to-rail inputs (see the Vicr parameter on page 6).

 

Rail-to-rail means the circuit input and/or output can operate up to the supply rail voltages.
The LM311 output can operate rail-to-rail, since the output is an open collector transistor, but not the input.
As shown here for ±15V supply rails, the input can only operate to within about 2V of the plus rail and within about 0.5V of the negative rail.
Anywhere in between those two voltages is fine.

 

The MIC7211/7221 advertised as rail-to-rail. In SOT-23-5 package.

 

Hello everyone

I have a question about rail-to-rail comparator and I am not sure if this is the right forum

anyway

can anyone tell me what is rail-to-rail comparator and what its difference from the normal comparator?

Should I use LM311 to obtained rail-to-rail comparator or one can get this type with any other integrated circuit

and what is the physical meaning of the term (rail-to-rail)?

thank you in advance

A large proportion of comparators have open collector outputs, that's about as rail to rail as it gets - until you load it.

Are you thinking of input common mode range?

The 311 is pretty ancient - there's certain to be better choices now.

If you need the output to go right down to GND; see if there's any CMOS types - but again, they won't do it if you make them sink a lot of current.

 

Thank you all for your answers

as I understand from the answer that most of op-amp are rail-to-rail especially for the output. aren't them?

 

as I understand from the answer that most of op-amp are rail-to-rail especially for the output. aren't them?

No. Most are NOT rail-to-rail, either the inputs or the output, especially the older parts. Consult the manufacturers' data sheets and selection guides to find out.

 

That is correct.

Rail-to-rail means the circuit input and/or output can operate up to the supply rail voltages.
The LM311 output can operate rail-to-rail, since the output is an open collector transistor, but not the input.
As shown here for ±15V supply rails, the input can only operate to within about 2V of the plus rail and within about 0.5V of the negative rail.
Anywhere in between those two voltages is fine.

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