2
\$\begingroup\$

I'm using the Falstad circuits simulator. For some reason, I get a steady 6V input on V- part of the first op amp in a negative feedback connection. When I put another resistor between the voltage source and the op amp, the V- suddenly goes to around zero as it should be.

I don't understand why in the first picture instead of 0 volts at V- I get the whole 6 volts. Perhaps I missed something.

1

2

I don't get the zero voltage at V- when the voltage of the input is near the saturation voltage of the op amp.

enter image description here

\$\endgroup\$

1 Answer 1

1
\$\begingroup\$

I don't understand why in the first picture instead of 0 Volts at V- I get the whole 6 Volts. Perhaps I miss something.

In your first picture, you have defined the inverting input voltage to be 6 volts by placing the voltage source without a series resistor. How can you expect it be anything other than 6 volts?

my second question, when the voltage reaches saturation of the op amp. I understand that it is a "problematic" voltage.

It's very much problematic in that the op-amp output can no-longer act to keep the non-inverting input at 0 volts.

\$\endgroup\$
9
  • \$\begingroup\$ You are right. But I'm confused about the fact, that in negative feedback V- should be zero if V+ is grounded \$\endgroup\$
    – KrtekUser
    Jun 24, 2023 at 16:02
  • \$\begingroup\$ The "hard" 6 volts placed at the input destroys the negative feedback. \$\endgroup\$
    – Andy aka
    Jun 24, 2023 at 16:03
  • \$\begingroup\$ May explain why? \$\endgroup\$
    – KrtekUser
    Jun 24, 2023 at 16:03
  • 1
    \$\begingroup\$ Thank you, sir! \$\endgroup\$
    – KrtekUser
    Jun 24, 2023 at 16:05
  • 1
    \$\begingroup\$ Thank you very much! \$\endgroup\$
    – KrtekUser
    Jun 24, 2023 at 16:11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.