Controlling a PC fan using temperature

[alip01]

Hi,

I am going to be making an LED array using 5x 3W LEDs. I will heat sink them, but to improve the heat dispersion, I was planning to fit 2 PC fans to the array's housing. In order to make them quieter, I was thinking about fitting a system that uses the temperature of the array to change the speed of the fans, so that when the LEDs are cool, the fans would be at a low speed (or not on at all) and when the LEDs were hotter, the fans would be at a higher speed.

Having Googled the idea, there seem to be a few variations, some more complex than others such as these:
**broken link removed**
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**broken link removed**

Which of these methods would be most suited for my purposes? Or are there any other methods that might be better?

Thanks,
Alistair

 

[Boncuk]

In order to control a fan efficiently google for PWM controlled fans.

A 12V fan won't run sufficiently at lower than 8V being voltage controlled by a bipolar transistor.

PWM switches the fan at full 12V (minus small losses) at variable pulse lengths, resulting in more motor torque, not to stall the motor at low supply voltage.

Take a look at that link: **broken link removed**

Boncuk

 

[Reloadron]

I agree with Boncuk that PWM is the best way to do this. Attached is an example of using a simple PWM controller. The image was taken from here. The data sheet for the chip can be found here.

The circuit is simple and adjustable. I would also think a single 80mm fan would work fine rather than two.

Ron