DC photoelectric switch circuit

Published:2011/5/24 2:05:00 Author:John | Keyword: DC photoelectric switch | From:SeekIC

Phototransistor BPX25 in Figure (a) stops where there is no light irradiation. So the no base current of transistor BC141 is off. Otherwise, the transistor opens to trigger thyristor to conduct. Then, voltage is on the negative cut-off side. The Figure (B) shows the opposite situation. When light shines into the phototransistor, the transistor BC141 conducts to cut-off the thyristor. Then the load-power cuts off. When there is no light, the transistor BC141 deadlines. So the DC voltage is added to the poles of thyristor through the resistors with resistance of 470Ω and 47Ω. Then the thyristor conducts to connect load circuit.



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