Exhaust fan automatic control circuit (1)

Circuit working principle: S1 and S2 are switches installed on the door frame . When the door is open
, they are disconnected and the circuit does not work. If someone enters the bathroom and closes the door
, S1 and S2 are pressed together at the same time, and the exhaust fan M is powered on. At the same time, the secondary DC voltage of transformer T
passes through S, to C. Fast charging, charging to the power supply voltage instantly. The composite tube
also receives base current through the 100 kfl resistor and is turned on, and the relay K is closed. When you open the door and walk
out of the bathroom, S1 and S2 pop open, and the exhaust fan is energized by K's self-protection contact K1 to continue
working. At the same time, S cuts off the base power supply of the composite tube, but the voltage on C passes through
the 100 kfl resistor, causing the composite tube to form a discharge circuit and maintaining the conduction of the composite tube, so that K maintains
the pull-in state. Until C. When the voltage on the exhaust fan is not enough to make the composite pipe conductive, K will be released
, causing the exhaust fan to stop working after a delay, which is more conducive to
exhausting the waste gas in the bathroom. The length of the delay time is determined by C. Determined by the value of C. Large
delay time, C. Short hour delay. S, for manual switch .