Circuit Design of Automatic Temperature Control and Speed ​​Regulator for Electric Fan

　　This is an automatic temperature control speed regulator for an electric fan. It can automatically adjust the speed of the electric fan according to temperature changes. The circuit can be adjusted and it can also be used to control other electrical equipment.

　　Working principle of the circuit: The IC in the figure is a 555 time base circuit, which forms a multivibrator with components such as R2, R3 and C2, and can send a rectangular wave signal with adjustable duty cycle. When the temperature changes, the resistance of the thermistor changes, changing the duty cycle of the square wave output by the multivibrator, adjusting the conduction angle of the bidirectional thyristor VT, thereby changing the voltage at both ends of the fan electrode, and automatically adjusting the speed of the electric fan. Component selection The integrated circuit IC uses the NE555 time base circuit, and models such as LM555 and TLC555 can also be used. VT is a bidirectional thyristor, its withstand voltage should be above 400V, and the rated current should be reasonably selected according to the capacity of the controlled electric fan. Resistors R1~R5 can choose ordinary 1/8 or 1/4W carbon film resistors; Rt is a negative temperature coefficient thermistor, and a thermistor with a resistance of about 10KΩ at room temperature can be selected. Capacitor C1 uses an ordinary aluminum electrolytic capacitor; capacitors C2 and C3 use polyester capacitors. VD is a voltage regulator diode with a voltage regulation value of 9.1V.