Circuit Project Electronic

Suitable for computer cooling fans
LED motor speed indicator

Requested by some correspondents, this simple design allows an accurate speed control of 12V dc fan motors, proportional to temperature.
A n.t.c. Thermistor (R1) is used as temperature sensor, driving two directly coupled complementary transistors wired in a dc feedback circuit.
An optional circuitry was added to remotely monitor fan operation and to allow some sort of rough speed indication by means of the increasing brightness of a LED.

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 Resistor
R5______________22K 1/2W Trimmer Cermet or Carbon
R6_____________680R 1/4W Resistor (Optional, see Notes)
R7_____________470R 1/2W Trimmer Cermet or Carbon (Optional, 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.

Related Links
More circuit about Electronic Control
More Motor Speed Controller
More circuit Temperature Control

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http://www.redcircuits.com//Page109.htm
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