this simple design allows|permits an correct speed control of 12V dc fan motors, proportional to temperature. A n.t.c. Thermistor (R1) is employed as temperature sensor, driving two directly coupled complementary transistors wired during a dc feedback circuit. An optional circuitry was added to remotely monitor fan operation and to permit some type of rough speed indication by means that of the increasing brightness of a LED.
Notes:
- 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.
