Hi,
I use this circuit below to compare different voltages.
When these two voltage equals, opamp output oscillates(I measured "A" point)
I used 1000uf capacitor, oscillation has decreased but not completely.
How can I solve this problem?

 

hi.
You need to add hysteresis to your OPA, say a 1meg resistor from the output to the input pin #3.
E
Remove the 1000uF cap.

 

hi.
You need to add hysteresis to your OPA, say a 1meg resistor from the output to the input pin #3.
E
Remove the 1000uF cap.

Hi,
I've tried but oscillation oscillation goes on.

 

hi,
Try a lower value say 470k, is there any electrical noise superimposed on either of the input lines.?
E

 

In schematic no C on OpAmp supply pin, Should have a Tant and a .1 uF ceramic.

Cap selection (not all caps for same value equal ESR performance) -

Regards, Dana.

 

The opamp probably is not oscillating. When the two input voltages are close, the opamp is acting as a linear amplifier, boosting the input signal noise by about 25,000 and presenting it to the output.

This is a relatively low gain opamp, so it will take more than the usual amount of hysteresis to calm it down.

ak

 

The opamp probably is not oscillating. When the two input voltages are close, the opamp is acting as a linear amplifier, boosting the input signal noise by about 25,000 and presenting it to the output.

This is a relatively low gain opamp, so it will take more than the usual amount of hysteresis to calm it down.

ak

Hi,
I use LM324 and TLC271.

 

hi,
Try a lower value say 470k, is there any electrical noise superimposed on either of the input lines.?
E

I've tried 68K and it has worked.
I used this example:

 

hi ilgin.
Thanks for posting your solution.
E