Resources about using opamp as comparator

[vdaniel]

Some old times OpAms worked good as comparators. There are several reasons to use OpAmp in comparator mode.
Does anybody have an experience of such usage for the modern OpAmps, recommendations, references?

Thanks in advance,
Varuzhan

 

[chinito]

opamp comparator

I don't know about other applications but for high speed converters, you can't use opamp as comparator for obvious reasons (speed). The comparators I've seen are always low impedance at all nodes to place poles associated with those nodes at higher freqs, distribute the gain in stages, utilize latches to drive output to CMOS levels and on and on ...

 

[liujs_825]

op amp comparator

They say the op amp has something difference with the comparator. For example,
comparator does not need compensation.

 

[surianova]

op amp as comparator

If a high gain opamp use in open loop without any feeback, will consider as comparator because for small difference voltage for the differential input, it
will give output either high or low. And as comparator use in open loop, it
does no need compesation.

 

[IanP]

op-amp comparator

There are 3 groups of comparators:
- universal (tpd -propagation delay time 30 - 200ns)
- precision (low offset voltages, high impedance, tpd not very important)
- fast (tpd<30ns)
First two goups can be easily replaced by fast amplifiers with 100 of MHz of bandwidth and very high slew-rates (1000V/µs and more)
However for very fast applications because of internal comensation it is always better to use proper "tool" which will be fast comparator with output designed to drive CMOS/TTL gates ..

 

[saturn]

op amp comparator hysteresis

Hello,
Check this:

**broken link removed**
**broken link removed**

 

[vdaniel]

op amp as a comparator

Tha main reasons of the OpAmp as comparator usage are:
1. Most of more or less fast comarators have large bias current
2. Sometimes simmetrical hysteresis is needed, using positive feedback
3. Sometimes large input voltage rating and output swing is necessary
etc.
In one schematic, for example, I have used a LM6161 (though its bias current is not small) as comparator, because its large input voltage rating, and because the same part is used in the analog front end of the same design, just to reduce the BOM.

That is why I am asking for real experience or exact recommendations, not a general thoughts.

Varuzhan

 

[pixel]

comparator opamp

Here is the link to one useful article on this topic:
Ask The Applications Engineer—31
By Reza Moghimi
AMPLIFIERS AS COMPARATORS?

https://www.analog.com/library/analogDialogue/archives/37-04/comparator.html

 

[vdaniel]

ua741 comparator circuit

Thank you, this is really valuable answer.
Unfortunately I could not find how to add your poins for help.
Varuzhan

 

[mohammad mokhtar]

operational amplifier - comparator mode

Hi
I do not recommend using opamp as a comparator because comparators has very low rise and fall time,which means low switching losses especially if efficiency is important like converters,inverters.....etc

 

[Kral]

ua741cn comparator

Some comparators have open Drain/Collector outputs. This is convenient when the output "1" state voltage must be different than the supply voltage. You can supply a pullup resistor to an external voltage source to get any "1" state voltage you need (within the rating of the output transistor, of course).

 

[vdaniel]

experiment with op amp comparator

Dear colleagues,

Please, read the good information from the Analog Devices, referenced by "pixel" and you will understand, that the problem is not so trivial, as many of you imagine.

Varuzhan

 

[nomad]

ua741 as comparator

so can someone help me? i use ompamp as comparator for pwm. i compare the 555's triangular wave with a dc control voltage. and the output of the comparator drives the mosfet. switching frquency is about 20khz.is that frquency is too high for the opamp?for example,how about LM1458 or UA741?and one more question: if i connect the pin for the negative supply voltage(-15v) to the ground, what happens?doing that is not ok?thanx you all!waiting for your help!...

 

[vdaniel]

op amp comparator as timer

I do not think, that LM1458 or uA741 are a good choice, if you want to work with single supply. Their input voltage range us about 3V above the negative rail. But
for 20kHz you can use LM358 with the negative supply pin (4) grounded. I recommend to provide a small hysteresis.

Varuzhan