I wanted to control the speed of a very fast and noisy brushless dc cooling fan. The fan I have is a 3 pin 12v 6.3w 120mm fan by Delta Electronics. From what I've learned from the internet is that the speed for 3 pin fans are adjusted by reducing the input voltage and 4 pin fans have an inbuilt pwm controller. However, I have seen some videos where the speed of 3 pin fans being easily controlled by an Arduino using mosfets.
What I want to know is whether trying to control the speed of my fan with a pwm output destroy the inbuilt electronic circuitry of the bldc fan or not. I have a small 2 amps pwm motor speed controller with me that might emulate what the Arduino just did. But, can bldc motors simply be controlled by pwm just like regular small motors?