Simple  Overvoltage Protection

I saw this overvoltage protection circuit from theoryCIRCUIT. I was wondering if instead the LED indicating that voltage continues to flow, we could instead make the LED turn on when overvoltage occurs, like it reaches 5.1V from Zener.

So the output is hypothetically attached towards an Op-Amp input, once it reaches a specific voltage set by the zener voltage then Q1 conducts then Q2 becomes open.

Link: https://theorycircuit.com/simple-overvoltage-protection-circuit/

  • \$\begingroup\$ It might be better if you explained how you want to use that circuit. I have significant doubts that it won't prevent short term overshoots of a couple of volts above 5 volts occurring. You should also provide a hyperlink to that picture. \$\endgroup\$
    – Andy aka
    Feb 20 at 13:14
  • \$\begingroup\$ Maybe you can add a resistor and an LED (like R4 and D1) in parallel with R3. \$\endgroup\$
    – Saadat
    Feb 20 at 13:35
  • \$\begingroup\$ @Saadat The Led would be supplied through base of Q2, so it would glow all the time. \$\endgroup\$ Feb 20 at 13:49
  • \$\begingroup\$ @MichalPodmanický You are right. I missed that part! \$\endgroup\$
    – Saadat
    Feb 20 at 14:42

1 Answer 1


Just use another BJT to drive the LED:

enter image description here

  • \$\begingroup\$ Thank you! I was a bit confused back there. \$\endgroup\$ Feb 20 at 13:43

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