This circuit of automatic Control suhu is based on two transistors that can be used to control the speed of a 12 V DC fan depending on the temperature (suhu). A thermistor (R1) is used to sense the temperature. When the temperature increases the base current of Q1 (BC 547) increases which in turn 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 more and so do the speed of the motor. Also, the brightness of the LED will be proportional to the speed of the motor.
Note:
- R1 can be a 15K @ 20°C ,N.T.C thermistor.
- M1: DC Fan 12V,700mA fan motor.
- Capacitor C1 must be rated 25V.
- The circuit can be powered from a 12V PP3 battery or 12V DC power supply.
About thermistor
The standard leaded thermistors are calibrated and tested at 20 °C to a tolerance of ± 5 % or ± 10 %; however, tighter tolerance, point matched thermistors are readily available as are special point match temperatures to fit your application. Since these thermistors have only one controlled point of reference (the point match temperature), the resistance at other
temperatures is given by the “Resistance vs. Temperature Conversion Tables” for the appropriate material curve. The resistance value at any temperature is the ratio factor times the resistance at 25 °C. The resistance vs. temperature conversion tables can
be found at: www.vishay.com/doc?33004 and www.vishay.com/doc?33011.
temperatures is given by the “Resistance vs. Temperature Conversion Tables” for the appropriate material curve. The resistance value at any temperature is the ratio factor times the resistance at 25 °C. The resistance vs. temperature conversion tables can
be found at: www.vishay.com/doc?33004 and www.vishay.com/doc?33011.
