07-10-2010, 11:15 AM
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Circuit Generates Analog Fan-Speed Control
Abstract:
A linear circuit measures temperature and controls the speed of a cooling fan by generating a variable supply voltage for the fan. Fan noise is becoming a larger issue as more electronic equipment enters the office and the home. A variable speed fan permits slower, and quieter, fan speed when temperature conditions allow. Fan-control circuits range from simple switches that boost the fan speed at a certain temperature, to digitally controlled fans with continuously-variable speed. High-speed/low-speed switches are inexpensive, but the sound of sudden speed changes can be annoying. Digitally controlled fans perform well, but those circuits are more costly, and the system must include a serial bus. This application note presents a low cost, self-contained analog circuit for fan-speed control (Figure 1), which is easily adjusted for any desired linear relationship between the fan voltage and temperature (Figure 2, Curves B and C). Actual data points are plotted against the desired voltage in Figure 2.
