I have PWM signal from a computer motherboard to control 2 fans, one of them is rated for 3000 RPM, and the other one is rated for 2000 RPM.

I'm trying to run all of them at the same speed(for example 1500 RPM) but I can only send one PWM signal, if I send PWM signal with 50% duty cycle one fan will run at 1500 RPM and the other will run at 1000 RPM.

So I was wondering if it is possible to take a PWM signal and modify it(Increasing duty cycle) and then feed it to one fan so that they run at the same speed.

Thanks in advance.

  • 3
    \$\begingroup\$ @Atizs It is PWM. How will a frequency divider help? \$\endgroup\$
    – HandyHowie
    Mar 13, 2019 at 13:46
  • 2
    \$\begingroup\$ Simplest option might be to put a voltage regulator on the faster one. The control chips in these fans are usually a device with an integrated Hall sensor and switch for the single phase motor, and have no speed regulation built in, so the speed is proportional to the supply voltage AND the PWM duty cycle. \$\endgroup\$
    – Phil G
    Mar 13, 2019 at 14:04
  • \$\begingroup\$ I do not like "is it possible" questions because I can answer yes or no and that would be a valid answer. I could answer no and then the next day someone does it anyway. You propose to modify a PWM signal. No one does that! It is do easy to generate a PWM signal (almost any microcontroller can do it) that we can simply generate a new PWM signal. Also why not simply use two identical fans? Maybe you could connect a resistor in series with the 1500 RPM fan to slow it down. \$\endgroup\$ Mar 13, 2019 at 14:22
  • \$\begingroup\$ Thank you for your help. \$\endgroup\$
    – user48739
    Mar 13, 2019 at 15:34

1 Answer 1


Some options for you. 1) Replace the 2000 rpm fan with a 3000 rpm fan - both use the same drive signal. 2) Use a microcontroller to stretch the pulse width. 3) Build a complicated analog circuit to stretch the pulse width. Determining the best one for you depends on your circumstances, which are not described in the question.

  • \$\begingroup\$ Thanks, I think I will go with the microcontroller option. \$\endgroup\$
    – user48739
    Mar 13, 2019 at 15:35

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