i've designed this schematic using a simple buck converter (LM2596) for my board that powers up some leds and board peripherals.

The board will work at 5V with maximum current draw of 2.5A.

Now, as you can see in the schematic, i've already added a reverse voltage protection using SS34 (D6) diode (Datasheet here), what i want to implement is the overvoltage protection, i want that if there is a voltage input of more than 15V the external peripheral (marked with netflag +12V-POE) will not start blowing up (as the external peripheral maximum voltage rating is 15V).

What i can use? a Zener (in this case what part you recommend) or something different?

enter image description here

  • \$\begingroup\$ The LM2596 is rated up to 40 odd volts so what are you actually trying to achieve here? D5 doesn't seem a very sensible idea. What are you trying to protect from overvoltage and what has this got to do with the LM2596? \$\endgroup\$
    – Andy aka
    Dec 18, 2020 at 13:44
  • \$\begingroup\$ The D5 might not be here, i have removed it, is pretty useless. I need to protect a device that is wired in parallel to the LM2596 using the netflag +12V-POE and the maximum rating voltage is 15V \$\endgroup\$
    – VirtApp
    Dec 18, 2020 at 13:52
  • \$\begingroup\$ Your title is "LM2596 - Overvoltage protection" - can you explain why this is your title? \$\endgroup\$
    – Andy aka
    Dec 18, 2020 at 13:59
  • \$\begingroup\$ thanks Andy, i've changed the title of the original post \$\endgroup\$
    – VirtApp
    Dec 18, 2020 at 14:25
  • \$\begingroup\$ But, as far as I can tell, your question has got nothing to do with the LM2596 and its ability to produce a 5 volt output rail irrespective of it feeding a load that takes 2.5 amps or not. Why are you still mentioning this in the question - it just wastes people's time wading through the swamp. \$\endgroup\$
    – Andy aka
    Dec 18, 2020 at 14:43

1 Answer 1


Assuming that you only need to protect the +12V-POE output, we can ignore the LM2596 circuit.

A fuse and zener will protect against many faults, but depending on your current requirements, there may be a sweet spot where a slight overload will burn out the zener before the fuse blows.

An SCR crowbar circuit with a properly sized SCR is robust enough to handle any situation.

The zener voltages in the schematic will need to be adjusted appropriately. The default values in the simulator are not suitable.



simulate this circuit – Schematic created using CircuitLab


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