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.

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

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.

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