Light controlled electronic switch circuit

Light-controlled electronic switch, its "on" and "off" are realized by the conduction and blocking of the thyristor, and the conduction and blocking of the thyristor are affected by the brightness of natural light (or artificial brightness) controlled by the size. The device is suitable for use as lighting in streets, dormitory corridors or other public places, and can be used to control day and night lights to save electricity. Working principle: The circuit is as shown in the figure above. After the 220V alternating current passes through the bulb H and the rectifier full bridge, it becomes a DC pulsating voltage, which is used as a forward bias voltage and is added to the thyristor VS and R branches. During the day, when the brightness is greater than a certain level, the photodiode D shows a bottom resistance state of ≤1KΩ, causing the transistor V to cut off, and its emitter has no current output, and the unidirectional thyristor VS is blocked because there is no trigger current. At this time, the current flowing through the bulb H is ≤2.2mA, and the bulb H cannot emit light. Resistor R1 and Zener diode DW keep the bias voltage of the triode V from exceeding 6.8V, which protects the triode. At night, when the brightness is less than a certain level, the photosensitive diode D shows a high resistance state ≥100KΩ, causing the transistor V to conduct forward, and the emitter has a voltage of about 0.8V, causing the thyristor VS to trigger conduction, and the bulb H emits light. RP is a brightness selection component that realizes switching switching in the early morning or evening. Installation and debugging: During installation, put the soldered printed circuit board into a transparent plastic box and fix it, connect it in series with the controlled electric lamp H, and make it face the sky or a brighter space in front of the lighting window of the house. , avoid direct exposure to night lights within 3 meters. Debugging should be carried out in the evening, and the resistance value of RP should be adjusted so that the controlled electric lamp H starts to light up at an appropriate brightness.