Using a comparator LM311 to reverse an analog voltage 0V to 5V, to 5V to 0V

danadak

Joined Mar 10, 2018
4,057
An LM311 is not comped for a closed loop G of 1 or pretty much anything, no characterization
of phase margin, so using it as an OpAmp ill advised.

An LM324 or a RRIO type OpAmp part much preferred, but check its datasheet to see if it is unity G stable.


Regards, Dana.
 
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ericgibbs

Joined Jan 29, 2010
10,526
While I agree that a comparator is not the best choice for using as a OPA, it is possible to use a comparator for a low 'grade' OPA, if he adds external components, IF thats the only option he has on the bench.
 

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danadak

Joined Mar 10, 2018
4,057
Eric it has no compensation, its a recipe for an oscillator. Specifically missing in datasheet is phase freq response curves.

It might be possible to comp it externally, but thats no guarantee internally it won't take off
and generate RF.


Regards, Dana.
 

ericgibbs

Joined Jan 29, 2010
10,526
hi Dana.
I agree, but it maybe that the TS has no alternative device.
As always we get minimal information and feedback from a TS, so we have to make suggestions that will hopefully get the TS to open up in telling us what he his really trying to do.
We can then recommend better ways of getting the job done.
Eric
 

Thread Starter

Timbob123

Joined Sep 30, 2019
25
LM741 requires a dual supply to have an input range that includes ground. It also needs a positive supply of at least 10V to provide a 5V output.

What are your power supply restrictions?
One 5VDC supply, could use a higher voltage like 9V. The input is 0 to 5V, need 5V to 0V output.
 

Thread Starter

Timbob123

Joined Sep 30, 2019
25
Then use a RRIO OpAmp, one designed for single supply. What is the load on the output of the OpAmp ?

http://www.ti.com/amplifier-circuit/op-amps/general-purpose/products.html#~p78=In;Out


Regards, Dana.
Here is the question raised by a co-worker, trying to help him:
I am attempting to invert a DC single from torque transducer from -V to +V so that it can be read by a microcontroller. I am looking at op amps
and voltage comparators but I do not want the single to be amplified.

Single output is limited to 40mA.
Supply voltage is limited to 5VDC

Any suggestions on what component to use? I am considering a LM311P.
 

ericgibbs

Joined Jan 29, 2010
10,526
hi 123
You asked initially for
analog voltage 0V to 5V, to 5V to 0V

Now you say, transducer from -V to +V

Is it required to change 0v to -5V to 0v to +5V.?

E
 
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