Here is a Simple Circuit Temperature Controlled DC Fan primarily based on 2 transistors which will be used to control the speed of a 12 V DC fan looking on the temperature.A thermistor (R1) is employed to sense the temperature. When the temperature will increase the base current of Q1 (BC 547) will increase that in flip decreases the collector voltage of the same transistor. Since the collector of Q1 is coupled to the base of Q2 (BD 140), the decrease in collector voltage of Q1 forward biases the Q2 lot of and so do the speed of the motor. Also, the brightness of the LED are going to be proportional to the speed of the motor.
Notes.
- The R1 can be a 15K @ 20°C ,N.T.C thermistor.
- The M1 can be a 12V,700mA fan motor.
- The capacitor C1 must be rated 25V.
- The circuit can be powered from a 12V PP3 battery or 12V DC power supply.
- Assemble the circuit on a good quality PCB or common board.
