Power amplifier to drive a fan

Question

I'm pretty new to the field: I'm a hobbist. I'm trying to drive a fan (H412R) which runs on 12 V, 0.2 A with an Arduino board, as it is easier for me to generate a PWM signal to control the fan speed.

The problem is that the Arduino outputs at best just 5 V with 40 mA of current. Now my task should be to build a power transformer circuit that amplifies both voltage and current to the desired level. This is what I was thinking about:

• amplify the voltage using a boost circuit from 5 V to 12 V (the boost circuit would like the one presented in this article, with the PWM signal given by the Arduino)
• amplify the current using a transistor current amplifier from 40 mA to 200 mA Is this functional? Can this design help me achieve what I need?

In the end I think that this problem can be seen as a circuit that can amplify the power from 0.2 W to 2.4 W.

Answer 1

Sorry, but your idea simply won't work. Instead, do something like

^{simulate this circuit – Schematic created using CircuitLab}

Note that you will need a 12-volt DC supply.

One way to look at the circuit is that M1 both increases voltage AND increases current.

Be careful of the FET. It MUST be a logic-level FET, or it won't work.

R1 and R2 are just there to protect against the Arduino being accidentally disconnected, in which case the fan will turn off.

The + wire of the fan (red) goes to +12.

Answer 2

One way or another you need 12V. Your idea to boost it from 5V is possible, and maybe necessary; that's its own discussion. Using the Arduino PWM to control it? Not a good idea. Consider a pre-made step-up module instead (many based on the popular LM2577.)

Bear in mind that 200mA at 12V will equate to 500 - 600mA on your 5V supply. Plan accordingly.

If you have a choice for your power supply, use 12V. The fan accepts that directly, while your Arduino can accept 12V on its DC IN jack and make local 5V for itself. Much simpler. More here: https://support.arduino.cc/hc/en-us/articles/360018922259-What-power-supply-can-I-use-with-my-Arduino-board-

Back to the fan. This cooler (H412R - link) has a 4-wire type fan with a separate PWM input. It can accept 5V PWM drive directly from the Arduino, no need for a FET.

Wiring diagram:

From here: arduino - how to read and control the speed of a 12V - four wire fan?

Answer 3

Amplification, Is NOT getting one thing and make it bigger. Instead, it is "making a bigger copy" of that thing that follows all actions of that former tiny thing. Look at the answer of WhatRoughBeast; the MOSFET is copier here:

• It "looks" at arduino output which varies from 0~5v with little current, controlled by your software.
• It makes a bigger copy of that same variation which has 12V supply and have more current to offer and can go [theoretically] from 0~12 with the same shape of the arduino output.

Notice, that the copy exists in another power "space" which is 12V and have more current to offer because we couldn't create the copy with desired specifications, in the arduino's same space which was 5V with lower current capability.

The same approach applies to audio amplifiers; an amplifier creates a powerful sound with another power supply unit, but mimics the tiny audio sound you make by using a tiny microphone. So the result, is a powerful audio that sounds just like what you said on the microphone. Sure, the copy may not be so accurate that's why audiophiles love amplifiers that are good "copiers" which call them HiFi equipment.

Disclaimer: it is a very basic concept of those things which would help to understand amplification.