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Maxim > Design Support > Technical Documents > Application Notes > Automotive > APP 1125
Maxim > Design Support > Technical Documents > Application Notes > Temperature Sensors and Thermal Management > APP 1125
Keywords: analog, fan speed control, temperature sensor, fan controller, thermal management
APPLICATION NOTE 1125
Circuit Generates Analog Fan-Speed Control
By: Jim Christensen, Strategic Applications Engineer
Jun 26, 2002
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.
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