Hello again

I connected a subtractor (difference) circuit and it was worked correctly when I was connected constant DC voltage supply to their inputs

The problem appeared when I connected a TTL signal source

The output is wrong and constant

The aim of my circuit is to subtract a constant from my variable input

Please can anyone tell me the mistake in my circuit

note I tried both 741 and LM358 op amp

 

You have the op amp plus and minus inputs backwards.
The way it is shown gives positive feedback and thus latchup at the output.

 

You have the op amp plus and minus inputs backwards.
The way it is shown gives positive feedback and thus latchup at the output.

But this is the subtractor circuit as shown in references

So, what do you suggest to do to overcome this problem

 

But this is the subtractor circuit as shown in references

So, what do you suggest to do to overcome this problem

A simulator showed the wrong result. You asked for help. You received help. Two other experts agreed. Quit believing your references after three experts and a simulator showed you that your reference was incorrect.

 

Have you tried Swapping pins 2,3 round??

 

But this is the subtractor circuit as shown in references

Either your references are all incorrect, or you miscopied the circuit, take your pick.

 

As an op-amp noob myself, I was surprised and disappointed to find that there's no standardization whatsoever in how op-amps are shown in schematics. I had a lot of head scratching confusion until I realized that I just have to check the plus/minus signs very carefully for every input (power supply and signal) every time. As long as I do that, I have pretty good luck now!

To sum up, I totally understand how the thread starter got confused on this, but I'm pretty sure it's time to trust the experts and just swap those inputs!

 

Have you tried Swapping pins 2,3 round??

View attachment 131931

Thank you, I discover the mistake.

the feedback should be taken from the inverting terminal of the operation amplifier

now my circuit work correctly

thank you again

 

Who can help me with the same problem?

 

Who can help me with the same problem?

If you have the same problem then just use the same solution.

 

Thank you, I discover the mistake.

Looks to me like Crutschow discovered your mistake, in post #2.

Bob