I'm looking to design an over voltage protection (for > 13-14V situations) on the input of a power supply (the PS is taking input from a 12V vehicle). I was considering only using a crowbar circuit for OVP + a fuse on the input of the crowbar for overcurrent.

I know crowbars are preferable to TVS for sustained over voltage conditions, but TVS can offer better transient response. I was planning to add the TVS after Q2, since a fast transient may pass thru but I could intercept it before hitting the power supply input. Wouldn't another option be to find faster switching transistors?


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Spikes can be filtered out after you define load. Vbat =14.2 nom +/-0.2 and need for Vmax \$\endgroup\$ Apr 7, 2022 at 19:29

1 Answer 1


What kind of power supply? For what load?

Crowbar (+ fuse) was often used with loads such as high-frequency Tx RF power amplifiers, to protect against fast overcurrent (default time < 5 ms) with antenna load mismatch or disconnected.
But now, amplifiers are protected electronically against "reflected voltage" (Z mismatch or VSWR too high).

The main problem with battery power supplies is generally with "short circuit" loads.
A transient overvoltage can be "sustained" by a good design.

  • \$\begingroup\$ It's an LDO that takes 12V and turns it to 5V for some MCUs + other stuff. There is no battery here actually. Just need to protect the downstream electronics \$\endgroup\$
    – jonnyd42
    Apr 7, 2022 at 23:58
  • \$\begingroup\$ What I meant was that current circuits are, in principle, sufficiently protected against short circuits and some "type" of voltage overload. A crowbar circuit might possibly be useful, just in case ... :-) \$\endgroup\$
    – Antonio51
    Apr 8, 2022 at 5:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.