Homemade Fan controller

[Greeny1994]

As the title suggests I'm going to make a fan controller.
I'm an electronics student and have lots of components at my fingertips, I can also get my hands on PIC microcontrollers and program them.

So far I have made one out of a 555 timer using PWM but it had that annoying fan scream, adjusting the design with a cap across the MOSFET output removed the scream but introducing more load/different fans reduced its effectiveness.

I am thinking of a high frequency PWM circuit (555 or PIC) or using a rotary switch with Zenner diodes hooked up to a darlington pair to act as a variable voltage regulator. Heat could be an issue but I have big enough heatsinks lying around.

Any ideas/circuit diagrams would be helpful.

Thanks
Matt

 

[Tealc]

If you are getting PWM scream you might want to try increasing the frequency of your timer so that it goes above 20kHz or so. There's a good reason why Intel specify a 25kHz PWM Alternately have it really low frequency.

When I've tried it I got the scream as well, but then I don't remember if I went upwards of 20kHz. In the end I never developed a fan controller out of that type of circuit, although I did buy parts to do it.

In the end I went for a circuit that converts PWM into DC and that worked out OK and as a bonus doesn't need manual interaction.

 

[Greeny1994]

I did manage to get above 20khz but at the low end I was getting the scream, so it would need a little bit of modification. Some how I did manage to fry a 555 but I think that was due to a bad circuit design on the internet.
I do currently have a LED dimmer built as part of my A level project so I may copy that and adjust it slightly.