Circuit provides efficient fan-speed control


Posted on Sep 19, 2012

As Moore`s Law plunges us into the realm of multigigahertz processors and PCs with gigabytes of RAM, engineers face the task of removing the heat that these state-of-the-art components produce. Cooling such systems poses a dilemma. If you optimize the fan size and speed for nominal operating conditions, the system is susceptible to failure when conditions deteriorate. If, on the other hand, you select the fan to maintain acceptable operating temperatures under worst-case conditions, the fan may produce an annoying level of sound. Controlling fan speed is the obvious solution.



Power comes from the 12V supply, and a dc/dc converter, IC1, steps down the input voltage to an intermediate voltage for powering the fan. The transfer function of this voltage is a function of resistors R1 and R2 and thermistor RT1. The thermistor is an




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