[SOLVED] op-amp gain with positive feedback and positif input

[afifar]

I want to ask how to calculate gain of this op-amp circuit

when i simulated it i got constant output 11.1 V. how to get this output and why is output not a sinusoidal signal like the input ?

 

[godfreyl]

You cannot calculate gain for that circuit. The positive feedback makes it behave as a Schmitt trigger. The output is either at maximum positive output or maximum negative output.

If you increase the amplitude of the input sine wave above about 1V peak, you will get a square wave at the output. If you increase the input voltage to say 2V peak and compare the input, output and the signal at pin 3, you will see how it works.

 

[crutschow]

Positive feedback will typically lead to oscillations a latch-up of the circuit (as you observed).

If you want an amplifier then you need to use negative feedback.