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.
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Thank you.
