My Design

I tried to come up with a design where if the input voltage is bigger than -8 volts the output will be input, if smaller than -8 volts it will be grounded. I ran the simulation on LTSpice and it works as i intended but would it work in real life properly? I'm asking this because i searched for a desing for this purpose on the internet and couldn't find anything and we have never done something like this in classes.

  • 3
    \$\begingroup\$ Your circuit doesn't make sense as drawn. And by "bigger" do you mean more positive or more negative? What you describe is also not called a comparator; It has no name. Make a regular voltage follower and use a diode clamp (with current limiting resistor) at the input. \$\endgroup\$
    – DKNguyen
    Jan 3, 2020 at 14:45
  • \$\begingroup\$ Or you can clamp the output instead. Either will work. Output may be easier in your case. \$\endgroup\$
    – DKNguyen
    Jan 3, 2020 at 14:51
  • \$\begingroup\$ What model of opamp did you use? \$\endgroup\$
    – Voltage Spike
    Jan 3, 2020 at 18:59
  • \$\begingroup\$ I mean when it is -7, -6 or whatever the output will be that but if it is -8 -9 etc. the output will be zero. imgur.com/a/EiibDFD this is the response that i'm trying to get. Basically i want the circuit to be eliminated when the input is -8,-9,-10... \$\endgroup\$ Jan 3, 2020 at 19:48

1 Answer 1


This is unlikely to work as you intend with most op-amps. If the input signal is, for example, -4 V and the non-inverting input is held at -8 V then it will be 4 V below the negative supply pin.

Check the datatsheet for the device you used in your simulation (and forgot to link in your question) to see how far below the negative supply rail you are allowed to go.

  • \$\begingroup\$ Here is the output graph and specs : imgur.com/a/EiibDFD I used UniversalOpamp2 \$\endgroup\$ Jan 3, 2020 at 18:57
  • \$\begingroup\$ Please post relevant information into your question. That is a very different circuit to the one in your question. \$\endgroup\$
    – Transistor
    Jan 3, 2020 at 19:04

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