What is the simplest/minimal circuit or component i can use to drive and protect a fan from overvoltage and reverse polarity?

A mosfet per fan seens a option for reverse polarity, still if there's a better option would be cool since i don't want to do switching or turn off or on digitaly. And what about overvoltage? For example if i plug 34V supply?

Fans are 24V @ 1A.


2 Answers 2


A simple series Schottky diode will protect against reverse polarity.

Typically you would have polarized or distinctly separate connector types to ensure you don't use the wrong supply, but assuming you have not taken that basic design step, you need to decide what action to take on overvoltage.

  1. Blow a fuse, which seems rather drastic since this then means manual intervention to fix it. You may not be aware of the fuse blowing (if it's in a holder for example), so your first indication of a problem is when the fan does not start when you turn the power on. This may be long after you mis-connected the cable. There are endless circuits to provide this type of brute force protection. For example:

enter image description here

  1. Provide inline active turnoff protection with a FET for example (Google for overvoltage Load Switch ...there are many modern examples). For silent protection such as this, should you provide an indicator (for both reverse voltage and over voltage errors) for faults. An example here is the Fairchild/ONSemi FPF2281 which even provide an indicator port for an MCU or LED:

enter image description here

Note: You still need to use a series diode for reverse voltage protection.

Of course you should consider:

  1. Design your system with unique power connections so you cannot make this very basic mistake. You should never be able to mis-connect your fan in any sensible design.
  • \$\begingroup\$ Fans have it own connector like normal PWM fan 4 pin header, it should be simple to plug it right but we should never trust human factor and modified power adaptors, so best to take care of this too if possible :) I will take a reading on that solutions, thank you. I like the 2º solution, seens simple and easy to apply, there are any version for more voltage? up to 50V? \$\endgroup\$ Sep 18, 2018 at 18:08
  • \$\begingroup\$ If you read the datasheet you will see that they specify the working voltage ….most withstand from 50 to 100V when cutoff. \$\endgroup\$ Sep 18, 2018 at 18:39
  • \$\begingroup\$ I'm talking about 50v for VIN and VOUT, as i can see Max VIN is 29.0V. I'm asking that because i may use 48V-56V fans too \$\endgroup\$ Sep 18, 2018 at 20:42

Use a VDR / Varistor and a diode in series with a fuse.

If over voltage, the VDR will short and blow the fuse.

If reverse polarity is applied, it will also short and blow the fuse.

You can use a resetable fuse.


simulate this circuit – Schematic created using CircuitLab

  • 2
    \$\begingroup\$ Or a single Zener diode to replace the VDR and D1. \$\endgroup\$ Sep 18, 2018 at 3:38
  • 1
    \$\begingroup\$ I don't know if you can get a Zener that can draw 1+Amp at 24V \$\endgroup\$
    – Damien
    Sep 18, 2018 at 3:40
  • \$\begingroup\$ So it's safe to choose a 2A fuse? What would be a good varistor for this situation? And a resetable fuse will work the same as a fuse? Just replace a regular fuse with a resetable? \$\endgroup\$ Sep 18, 2018 at 3:58
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    \$\begingroup\$ @Damien Thats true, i think some people come with this anwsers for joke, obvious that not a good solution and in fact can be much more hard to implement, so hard to implement and expensive don't look like simple to me, solder 10 tiny smds should be easier than tie that zener up \$\endgroup\$ Sep 18, 2018 at 18:22
  • 1
    \$\begingroup\$ PTC resettable fuses aren't good for over-voltage protection! \$\endgroup\$
    – abhiarora
    Sep 27, 2018 at 11:25

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