Hi there, i have been trying to make a voltage regulator that is controlling a external dc power supply. I want to use it to control fan speed via pwm the fan i am using doesn't have pwm so i want to do it using voltage regulation. I had a circuit working with a transistor but i am worried that if i hook up to many fans it eventually will burn up. I have also tried it with a mosfet but this caused the fan to make a extreme high pitch whining sound. So if there is anyone that may have designed a circuit that can handle the power and control the speed. Or of a circuit with a mosfet that doesn't create the whining sound that would also be great.
A fan that is a motor with a blade assembly or the electronic sort as is mounted on a computer (usually has a black plastic frame)?
A fan as in a computer fan, a 12v DC fan to be exact.
Show us a picture of the fan.
Just wondering, how can a fan not be PWM?
This fan only has 2 leads it only has a positive and a negative wire it does not have a distinct pwm wire
What PWM period did you try?
I was using the default arduino pwm period during my tests
So 1 kHz or 500 Hz? no wonder it "sings".
Ohh well if that is the case i will try to change the frequency and see what that does. From what i can see i was using 1KHz
Try a more inaudible frequency. It's possible that the fan resonates at certain audible frequencies and not at others, as well.
Hi,
If yours is a computer fan, then it is a BLDC motor, a Brushless DC motor.
In the fan assembly it has an electronic control system that is expecting DC at 12V.
Feeding it with PWM pulsed DC will be causing it problems when it come to control the motor.
Some fans are okay with PWM supply, but others are not.
Your BLDC is basically a 3 phase AC motor with circuit that applies PWM signals to each phase in a timing sequence from the DC input.
Some BLDC do not perform well when powered below their rated input voltage.
Tom..... 
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2-pin or 3-pin computer fans are usually controlled with 30Hz PWM.
Low enough to not hear it (it could knock a bit), and low enough for the motor to work.
You must use a transistor (logic level mosfet) to switch the low (ground) side of the fet.
It could be better/easier to throw the 2-pin fan out of the window, and buy a 4-pin fan.
Or pull the 4-pin CPU fan off an old motherboard (try dump stores).
They can be driven directly with an Arduino pin.
The ~25kHz PWM they require (outside our hearing range) can be generated with the Arduino.
There is a code example somewhere on this site.
Leo..
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