[Diagram doubts] Control 12V fan speed with transistor

[lapislazulis]

Hey there!

I want to control the speed of a 12V fan using an Arduino (I'm using components I have at home), but I'm not sure if the circuit diagram I've designed is correct.

Details:

• The power source is a 12V – 2A adapter, connected to a small regulator board that outputs 12V (direct) to the fan and 5V to power the Arduino and the potentiometer.
• Fan: 12V – 0.18A
• Potentiometer: 10K

Questions:

• I only hace IRF520N transistor (but I can buy more models).
• Do I need a pull-down resistor to ground from the transistor's "Gate"?

Could it be something like this?

Note: I know it's oversized, but in the future, I'm going to add temperature and humidity sensors along with a small screen to control the enclosure of a 3D printer.

[jim-p]

Use an IRLZ44N MOSFET

Change the 100 ohm resistor to 10K and move it to the other side of the 150 ohm resistor.
Change the 150 ohm resistor to 330 ohms

Do I need a pull-down resistor to ground from the transistor's "Gate"?

Not really but I would leave it in just in case you may have problems later on.

Don't power the Arduino through a breadboard, connect the power leads directly

You have the Gate and Source backwards

[ledsyn]

@lapislazulis

I only hace IRF520N transistor (but I can buy more models).

With that FET you sure will have a controlled speed, but it won't be by PWM. Lowest RDS(on) spec'd is 10 V

@jim-p got a recommendation, and there are several more FETs to choose from. Try 'logic level MOSFET'

100 Ohms resistor needed? It's way too low - voltage divider calculation: 150/(100+150)*5=3
At 3 V it's doubtful that the FET will even turn on. Lets say you use a 100k resistor instead, that will pass 4.99 V. Is it needed? Its importance is low but nevertheless it makes sure that your fan is off when you start up the circuit.