I bought two fans for my PC case, but I accidentally ordered the 5V version of the fans. The box states that CAN'T be run on 12v of regular Motherboards or the'll die.

I happen to have a step-down voltage converter that can handle 12v and I can regulate it to 5v. So, with a little soldering I can solve my problem. My doubt is about that the fans are PWM and I intend to preserve that functionality.

I thought of connecting the +12 and GND to the buck converter and the PWM and TACH directly to the motherboard. I'm almost certain that it's OK to do it, but I want to be a 100% confident. I'm not sure if the TACH and PWM from a regular motherboard will have higher voltages than this fans actually supports.

Am I safe doing this?

PS: If you're wondering why I don't return the fans the answer is: Argentina.. shipping and custom taxes are more expensive than the fans itself and I bought the fans overseas..


The PWM output of the mainboard is usually a open drain configuration and it works with 3.3 V or 5 V, so it should work with the lower voltage fans as well.

The TACH signal is also a open drain configuration inside the fan. The mainboard however will have a pull-up to 12 V. I haven't found the specified maximum current for motherboards on that pin, but I guess it will be okay for the 5 V fan as well.

Noctua has a PWM specification which tells the maximum current is the same for 12 V and 5 V fans, so it should work fine (the current being independent because the pull-up is on the 12 V line of the motherboard).

You don't actually need a separate step down converter. 5 V is readily available inside your PC already - the red wires from an ATX power supply carry 5 V.

  • \$\begingroup\$ the red wires from an ATX power supply carry 5 V wow... Why I didn't think about that on the first place haha. Thanks man! \$\endgroup\$
    – KnF
    May 13 '19 at 15:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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