# how to solve this op-amp circuit?

I would appreciate some help solving this simple circuit which I'm trying for some time but can't seem to match with the given answer. Aim is to find output voltage $$\V_o\$$

for the given input voltage -

My attempt : Since the only current flow $$\i\$$ is from $$\V_O\$$ to ground via 4k and 1k resistors, and $$\V_+=V_{in}\$$ $$i(mA)=V_{in}/1$$ $$\Rightarrow V_o=V_{in}+i*4=5V_{in}$$

So that when $$\V_{in}\$$ vary from (-5 to -2); (-2 to 2); (2 to 5)., $$\V_o\$$ saturates at -10; varies linearly to 10; then saturates at 10.

But the output is given as -

Thanks,

Your circuit doesn't have negative feedback: -

Therefore it acts as a comparator with hysteresis and hence, the output changes state when the input voltage passes the hysteresis threshold points shown below in red dots: -

The non-inverting version is also known as a Schmitt trigger circuit: -

• ...and it took Andy 8 minutes to answer :-) This is rad... Andy are you an employee of StackExchange? Even for an employee this response time would be stellar.
– frr
Dec 16, 2020 at 13:42
• @frr I did a very simple answer when I first answered and built on it over the next 20 minutes. If it's worth answering, it's worth answering well. No, not an employee of stack exchange. Dec 16, 2020 at 13:44