PWM Fan speed 4 pin on 3.3v?

Hello I'm working on a arduino project that uses a 3.3v pro mini. I don't know if this is a problem or not. But On the Blue pin of a 4 pin fan there is a Speed controller using a PWM signal. On a Arduino Uno board I can control it with no problem on 5v Signal. But Sense I would like to use a Pro mini board and it is 3.3v tolerant Not sure that i would be getting Full Speed out of the fan. I haven't tempted it yet i thought i get some help first before i do.

I need some help can someone help me on figuring this out please? Thank you.

Hi Josep,

You can not get the full speed out of it. PWM is just a way of using a digital only signal (IO port) to create a fake analog signal. This is done by turning the digital port on and off with a certain interval at a certain frequency. The interval is called duty cycle and is usually given in percentages. So a 5v PWM signal at 50% duty cycle will be read as 2.5v (since if you average it being on and off for a while that is what you get). Thus if you run something at 3.3V you can get a maximum of 3.3V with the PWM (being always on so a duty cycle of 100%).

You can solve this by using a transistor and an external power supply. Since the transistor can switch the 5V signal in that case. (I presume there already is a 5V line somewhere since that is what fans typically run on).

Hope that helps.

5v proMinis are available also. You can get them cheap on amazon