As shown in the figure, the automatic control circuit of the ventilation fan. The circuit is composed of an AC step-down rectifier circuit (VDD=+9V), a toxic and harmful gas sensing head QM-N5, a temperature detecting circuit Rt, a bistable control circuit and the like. Among them, QM-N5 is a gas-sensitive semiconductor device, and Rt uses an MF-51 type NTC thermistor. professional 3 Light Modes with tripod stand&Phone Holder Deaktop USB-Powered Dimmable mini led selfie ring light Rgb Ring Light,Camera Ring Light,Ring Light for Photography, Led Soft Ring Light shaoxing shangyu Tianya Photographic Equipment Factory , https://www.tianyafoto.com
Under normal circumstances, when there is no harmful gas in the room or its concentration is within the allowable range, the resistance between A and B at both ends of QM is large, the potential at point B is lower than 1V, so that D2 and BG2 are cut off, and 555 is high on 6 feet. Flat reset, the low level output by the 3 pin makes the SCR cut off, and the ventilating fan does not work. When the concentration of indoor harmful gas exceeds the allowable value, the resistance of QM-N5 decreases rapidly, the potential of point B rises, D2 and BG2 turn on, and 555 is set by the 6-pin low level. The high level of the output turns the SCR on and the ventilator works.
When the room temperature rises, the resistance of Rt decreases, and the potential of point E rises. When the room temperature rises to about 36 ° C, both D1 and BG1 are turned on. 555 is set because the 6 pin is low level, and the high level output by the 3 pin makes the SCR turn on, and the ventilation fan operates.
The control circuit can realize the automatic opening and closing of the ventilation fan according to the change of the indoor harmful gas concentration or the change of the temperature. Thereby improving the indoor gas and temperature environment.
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