|Make RadioLocman Your Homepage!| DC Fan Controller Takes Bare
Bones Approach Fans can be necessary for circuit cooling, but
continually running a fan at a rated voltage will cause
mechanical failure, usually in the bushings or bearings. By
running it only when and as fast as needed, you can greatly
extend its useful life as well as the life of the equipment it
is cooling. A simple on/off fan control will work, but it can
cause switching transients and similar problems as the fan
cycles. A proportional controller that starts the fan when
circuit temperature passes a threshold, speeds up the fan as the
temperature rises, and slows down and stops the fan when the
circuit cools down is more elegant. Most proportional fan speed
controllers are far fancier than required, though, because
circuit cooling isn’t really a precise science. This simple
circuit is just as effective as a fancy design and has been used
many times with great success (Fig. 1). It requires only a
thermistor for temperature sensing, a FET to co