Automatic - light switch. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Automatic - light switch. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

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Automatic light switch allows you to automatically turn off the lighting during daylight hours.

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The machine consists of a light sensor - a photoresistor and a photo relay, made on transistors V1, V2, an executive circuit on thyristors V4, V10 and a full-wave rectifier on diodes V6, V7. The machine works as follows. With a decrease in illumination, the resistance of the photoresistor R3 increases from 1 ... 2 kOhm to 3 ... 5 MΩ, which leads to an increase in the collector current of transistors V1 and V2. As a result of this, the V4 thyristor opens, the R7, C3, V9 chain generates a pulse that opens the V10 thyristor, and the lighting lamps turn on.

With an increase in the illumination of the photoresistor, its resistance decreases, and the collector current of the transistor V2 also decreases, which leads to the locking of the thyristors V4 and V10. The lighting lamps go out, and the capacitor C3 is discharged through the diode V8 and resistors R5, R6 and R7. The threshold for turning on the machine is set by resistor R1.

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