I have an automotive application where I have this:


simulate this circuit – Schematic created using CircuitLab

Would the 20V 1W or 5W zener diode be enough together with a typical automotive fuse to protect the LCD drive in case there is a voltage spike. Fuse would be 2A as it should be enough for the normal operation of the driver and screen. The RBO40-40 clamps to 40V so there could be still some over voltage after it.

Edit: I have understood crowbar is useful for over voltage situations but in my case I am mostly worried about very short voltage spikes.

  • 1
    \$\begingroup\$ It won’t do much after the LDO and of the LDO survived the obervoltage in the first place, didn’t it clamp the output enough for you? \$\endgroup\$
    – winny
    Feb 1, 2018 at 15:31
  • \$\begingroup\$ RBO40-40 doesn't clamp enough, so there is the 40V > 25V situation. \$\endgroup\$
    – Petteri H
    Feb 1, 2018 at 15:48
  • \$\begingroup\$ automobiles can have up to a hundred volts spikes on their batteries, you need to have over voltage protection in front of your regulator. There are specific standards that address voltage pulses in automobile systems. might be worth to look at one, the voltages can get way higher than you think. \$\endgroup\$
    – MadHatter
    Jun 21, 2020 at 14:21

1 Answer 1


What you propose is a lower voltage (20V) Zener in parallel with the internal Transil (40V), it will work up to 20V but common zeners aren't designed for transient protection. I use the RBO40-40 before the electronic module voltage regulator, and another TVS in the output of this regulator, matched with it's output voltage. The RBO40-40 is designed to protect electronics acording IEC/ISO standards, maybe you can use a high input voltage regulator and the TVS in it's output.


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