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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\$

enter image description here

for the given input voltage -

enter image description here

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 -

enter image description here

Thanks,

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1 Answer 1

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Your circuit doesn't have negative feedback: -

enter image description here

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: -

enter image description here

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

enter image description here

enter image description here

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    \$\begingroup\$ ...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. \$\endgroup\$
    – frr
    Dec 16, 2020 at 13:42
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    \$\begingroup\$ @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. \$\endgroup\$
    – Andy aka
    Dec 16, 2020 at 13:44

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