Exhaust fan automatically starting circuit

Published:2011/7/5 8:56:00 Author:John | Keyword: Exhaust fan | From:SeekIC

The circuit is as shown. 220-volt power supply is divided into two routes. One route is transferred into a 5V power supply through the transformer, aiming to supply the control circuit. The other route is connected to the exhaust fan through the relay in series. As for control circuit, the 5-volt power supply gets DC power supply through the rectifier. Commonly, R3, the partial pressure of R3 can not be the transistor due to a smaller resistance. So the relay is not energized and the exhaust fan does not work. When the heater is heated, heat resistance of R3 becomes larger. And the partial pressure on the R3 would induct the transistor. Then the relay pulls and exhaust fan works.



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