![]() ![]() To transform line "A" into line "B", you must subtract a voltage offset from the temp sensor output and then multiply the result by a constant. Simply amplifying the MAX6605 output does not provide the 8V floor voltage, and the gain (9.58 = 0.114/0.0119) needed to obtain the fan-voltage slope is not the same gain (9.22 = 6.86V/0.744V) needed to obtain the y-intercept point. ![]() The floor voltage ensures fan rotation at low temperatures, and above 10☌, the voltage increases with a slope of 0.114V/☌ until it reaches full value at 45☌. temperature in ☌:Ĭurve "B" relates the fan voltage to temperature and combines a minimum "floor" voltage of 8.0V with a sloping line: temperature for the circuit in Figure 1.Ĭurve "A" on Figure 2 represents the output of a MAX6605 analog temperature sensor vs. As described in the text, these curves illustrate voltage outputs vs. This circuit delivers a continuous and linear fan-control voltage that is proportional to temperature.įigure 2. Actual data points are plotted against the desired voltage in Figure 2.įigure 1. 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). Digitally controlled fans perform well, but those circuits are more costly, and the system must include a serial bus. High-speed/low-speed switches are inexpensive, but the sound of sudden speed changes can be annoying. A variable speed fan permits slower, and quieter, fan speed when temperature conditions allow.įan-control circuits range from simple switches that boost the fan speed at a certain temperature, to digitally controlled fans with continuously-variable speed. A linear circuit measures temperature and controls the speed of a cooling fan by generating a variable supply voltage for the fan.įan noise is becoming a larger issue as more electronic equipment enters the office and the home. ![]()
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