Arduino DC fan controller BJT and mosfet setup help

Hi all,

I would like to control a DC Fan using a mosfet sinds i want to control it via PWM output pin 3 of a Arduino Uno.

I cant find the right setup of a BJT and a N type mosfet. I'm not well know with transistors and how to apply them, therefore i hope you can help me.

Some information for you to consider:

DC fan (blower): brushles, 7-12 V, 1.8A
PWM output: 900hz with duty cycle of 0-255

I found several setups like this, but this is what i was thinking, see attachment.

What type of resistor, BJT and or Mosfet should i use in this setup?? Or do i need to consider another easier setup??

Kind regards Lucas

Nick Gammon tutorial on driving motors or other loads with power transistors - Gammon Forum : Electronics : Microprocessors : Driving motors, lights, etc. from an Arduino output pin

A source-follower doesn't work.
The N-channel mosfet in your diagram needs a 5volt higher voltage on the gate than the source/drain.
You don't have that ~17volt available in your diagram.

You need a P-channel fet (or PNP transistor), high-side. With a second transistor as level shifter.
Diagram#3 in the link in post#1 is perfect to switch a 12volt fan high-side (in the + line).

If it's only a two-pin fan, then you can also switch/PWM the ground wire with an N-channel fet (diagram#1)
Leo..

It's possible that you can/could effect some reduction in speed (from its max).
But, the thing is, what you're dealing with is an "electronic fan".
There is a circuit board built into it. It's not the same as a brushed motor.

One thing to be aware of is that some fans are not just a motor, they may have other circuitry
(such as Hall-effect commutation sensors and decoupling capacitor).

Such a fan is not designed to be PWM'd at all (especially the decoupling capacitor will pull large
current spikes if you do PWM it).

A pure motor winding is inductive and is very happy with PWM.

Thanks all,

very helpfull!

I'm now beginning to wonder if a simpler fan with 2 wire (brushed) is a better solution for this issue.

I will order a brushed fan and try to work it out with the n-channel mosfet diagram #1.

Thanks for the help!

Hi All,

An update from my side,

I bought a cheap fan and went for schematic #1.
Played a little bit with duty cycle.
Works perfectly!

Thank you all for helping me out!

:slight_smile: :slight_smile: :slight_smile: :slight_smile: