Traditional Chinese Practical Exhaust fan automatic switch: Circuit Design, Parts List & Workshop Prototype Guide

Premium 8,910 credits (=$89.10) · Priced by article length · permanent access after unlock · 1 $ = 100 credits

Exhaust fan automatic switchWith the improvement of people's living standards, many household kitchens have installed exhaust fans, which can discharge cooking fumes and various smoke in a timely manner. However, since the exhaust fan does not have an automatic control device, it is necessary to manually control the opening and closing of the exhaust fan according to the actual situation during use, which brings inconvenience to the use. If the exhaust fan can automatically open and close according to changes in the air composition of the environment, it will not only eliminate ambient air pollution in a timely manner, but also create convenience for users. The automatic switch of the exhaust fan is designed to solve the problem of automatic exhaust air pollution.1． How the circuit worksThe automatic switch circuit of the exhaust fan is shown in Figure 63-1. It is composed of an "air bowl heating element" conversion element, which is a gas-sensitive semiconductor device. It is very sensitive to irritating gases such as cooking fumes, alcohol vapor, cigarette smoke, etc. When these harmful gases reach a certain concentration indoors, the exhaust fan will be automatically started to discharge them outdoors.Figure 63-1In the figure, the 220V power supply is reduced to about 100V by capacitor C1 and supplied to the detection electrodes A-A′ and B-B′ of the gas sensor QM; it is reduced to a voltage of about 3V by capacitor C2 and supplied to the heating electrode f-f′ of QM.In normal times, the resistance between the detection electrodes A-A′ and B-B′ is high, the triac SCR is cut off because the control pole has no trigger voltage, and the exhaust fan and alarm circuit stop working due to power failure. When the harmful gases in the air in the kitchen reach a certain concentration, the resistance between the detection electrodes becomes smaller, and the control electrode of the triac obtains the trigger voltage. The triac SCR is turned on, turning on the power supply of the exhaust fan and alarm circuit. The exhaust fan runs to discharge the harmful gases outdoors. The alarm circuit makes a sound to remind people that indoor harmful gases have caused air pollution and are being eliminated.The alarm sounding circuit is directly powered by 220V AC mains power. It is characterized by loud and crisp sound, safe and reliable operation, and overcomes the shortcomings of the low sound of the piezoelectric ceramic buzzer.During the positive half cycle of the AC input, the emitter of the triode BG is at a high potential and the collector is at a low potential; a positive feedback signal is formed through feedback between the feedback pole and the main pole piece of the piezoelectric ceramic piece, making the BG in a cut-off state; when the AC input is a negative half cycle, the BG is in a saturated conduction state through the positive feedback formed between the feedback pole and the main pole piece. In this way, the triode BG oscillates between the cutoff and saturation states at a frequency of 50Hz, and the piezoelectric ceramic chip emits a buzzing sound of 50Hz.2. Component selection and debuggingQM is a gas-sensitive semiconductor device, and QM-N5 or HQ-11 gas-sensitive tube can be used.N is a neon tube, which can be used in fluorescent lamp starters. …

Sign in to unlock

Login / Register

One-time payment per article, billed in credits (1 $ = 100 credits). You will review the invoice and the non-refundable digital-asset policy before anything is charged. The PDF is generated on demand and embeds a licensing watermark.