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Analog Fan Speed Control CIRCUIT (MAX6003)

2015-02-28 04:40  
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This article describes the Analog Fan Speed ??Control CIRCUIT (MAX6003). The content is very simple, very helpful. Components in this article can help you understand better understanding of this article. For example, in this article, you can go to find and buy these components:MAX6003.

The large issue today that caused by more electronic equipment enters the home and the office is noise of fan. to reduce fan noise, a variable speed fan is used because it permits quieter and slower, fan speed when temperature conditions allow. To build a variable speed fan we can use digital control or high-speed/low-speed switches. Digitally controlled fans perform well, but those circuits are the system must include a serial bus and more costly. High-speed/low-speed switches are inexpensive, but the sound of sudden speed changes can be annoying. We can use this circuit to solve that problems, it is self-contained analog circuit for fan-speed control and a low cost. Here is the circuit :

Analog Fan Speed Control circuit schematicCurve “A” on Figure 2 represents the output of a MAX6605 analog temperature sensor vs. temperature in °C:

Vsensor = 0.0119V/°C × Temp 0.744V.

Curve “B” relates the fan voltage to temperature and combines a minimum “floor” voltage of 8.0V with a sloping line:

Vfan = 0.114V/°C × Temp 6.86V.

We must subtract a voltage offset from the temp sensor output and then multiply the result by a constant to transform line “A” into line “B”. To determine the resistor values we can use this equation:

For the condition R2<<R1,

R1 is any reasonable value,
R2 = R1(AvVtemp0 – Vy-intB)/[(Av-1)(Vref - Vtemp0
Vy-intB/Av)], and
R3 = R2(Av-1),

Av = 0.114/0.0119 = 9.58 is the ratio of the desired slope in

V/°C to that of the temperature sensor,

Vtemp0 = 0.744V is the temp-sensor voltage at 0°C,

Vy-intB = 6.86V is the y-intercept indicated by the desired

(extrapolated) temperature curve, and

Vref = 3.0V is the reference voltage.
To calculate the floor voltage we can use this equation:
R5 = R6(Vfloor – Vref)/(Vref), where R6 equals any reasonable value, and

Vfloor = 8V is the desired minimum output voltage.
This equation is used for a desired temperature curve “C” :

Vfan = (0.114V/°C)(Temp 8.5V),

The required offset gain (8.5V/0.744V = 11.42) is greater than line “B” and the gain (slope) of Av = 9.58 is the same as for line “B”. This equation can be used for such cases:

R4 = R1(Vy-intC/Av – Vtemp0)/(Vref – Vy-intC/Av)
where Vy-intC = 8.5V is the intersection of the desired temperature curve with the y axis.

 


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