Temperature Controlled DC Fan
|Parts Name||Parts Symbol||Parts Description||Quantity|
|Thermistor||R1||15K (20°C, NTC)||1|
|Resistor||R5||22K (1/2W, Trimmer Cermet/Carbon)||1|
|Resistor||R7||470R (1/2W, Trimmer Cermet/Carbon)||1|
|Capacitor||C1||100uF (25V, Electrolytic)||1|
|Transistor||Q1||BC547 (45V, 100mA, NPN)||1|
|Transistor||Q2||BD140 (80V, 1.5A, PNP)||1|
|Motor||M1||Fan Motor (12V, 700mA max)||1|
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.
- R5 must be set to allow motor just starting at the desired temperature.
- Any n.t.c. Thermistor in the 6K8 - 22K range value might work, provided R2 value is one/tenth of Thermistor's value.
- R6, R7 and D1 are optional: R7 must be adjusted until the LED glows faintly when the motor is just running.