Smoke alarm circuit

Published:2011/6/28 2:58:00 Author:Christina | Keyword: Smoke, alarm | From:SeekIC

The smoke alarm circuit is composed of the infrared light tube, the series feedback photosensitive circuit (composed of the phototransistor), the semiconductor tube switch circuit and the integrated alarm circuit, as the figure 8 shows. When the monitored environment has no smoke, the infrared light-emitting diode VD1 lights with the pre-tuned initial current. This infrared light is received by the photosensitive transistor VT1 to reduce the resistance of VT1 amd increase the current of VD1 and VT1, so the luminous intensity of the infrared light-emitting diode VD2 increases accordingly. Figure: Smoke alarm circuit



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