| Temperature Controlled Fan | |
With this simple circuit you wish follow able to control the speed of a DC buff according to temperature measured by a temp sensor. It's an ideal add-on for your PC cooling fans to eliminate produced noise. Requested by some correspondents, this simple intent allows an accurate speed control of 12V dc lover motors, proportional to temperature. A n.t.c. Thermistor (R1) is used as temperature sensor, impulsive two directly coupled antonymous transistors wired in a dc feedback circuit. An optional circuitry was added to remotely proctor fan operation and to set aside more or less kind of rough rush indication past means of the increasing brightness of a LED.  Notes:
R5 must be set to earmark motor just start at the desired temperature.
Any n.t.c. Thermal resistor in the 6K8 - 22K range value mightiness work, provided R2 value is unity/tenth of Thermal resistor's value.
R6, R7 and D1 are optional: R7 must be adjusted until the LED glows faintly when the motor is just running. Parts:
R1______________15K @ 20°C n.t.c. Thermistor (See Notes)
R2_______________1K5 1/4W Resistor (See Notes)
R3_______________1K 1/4W Resistor
R4_____________270R 1/4W Resistance
R5______________22K 1/2W Trimming capacitor Cermet or Carbon paper
R6_____________680R 1/4W Resistor (Facultative, see Notes)
R7_____________470R 1/2W Trimmer Cermet OR Carbon (Nonobligatory, see Notes) C1_____________100µF 25V Electrolytic Capacitor D1______________LED (Optional, any shape and color, see Notes) Q1____________BC547 45V 100mA NPN Transistor
Q2____________BD140 80V 1.5A PNP Transistor M1____________Fan Motor 12V 700mA max.
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Downloads
Temperature Controlled Fan - Link
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