Lighting photo switch. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting. Control schemes
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The scheme is designed to automatically turn on street lighting at nightfall and automatically turn it off at dawn.
The circuit diagram is shown in the figure. Light level sensor - photoresistor R2 type FSK-1. It is connected between the base and the collector of the transistor VT1, so during the day, when the resistance R2 is low, this transistor opens, as the voltage at its base increases. As a result, the voltage on its collector drops and the transistor VT2 closes. The voltage on its collector increases, respectively, and the voltage between the control electrode of the triac VS1 and the power plus decreases, therefore, it closes and no voltage is supplied to the lamp H1 of the lamp.
With a decrease in the level of illumination, the resistance of the photoresistor increases, and with the onset of darkness, at some point, the transistor VT1 closes so much that the voltage on its collector becomes sufficient to open the transistor VT2. The voltage at the VT2 collector decreases, which causes an increase in voltage between the control electrode of the triac and the power plus to such a level that the triac opens and turns on the H1 lamp.
Unlike many other simple photorelay circuits, this one can use a photoresistor of nominal resistance in a fairly large range, from almost tens to hundreds of kOhms. The voltage at the base of the transistor VT1 is determined by the divider of R3 and R2. At the same time, the resistance R3 is variable, and with its help it is possible to configure the circuit not only to work with a photoresistor of almost any nominal resistance, but also to almost any daylight threshold.
Additionally, in order to prevent the lamp from flashing when the illumination changes rapidly, as well as to prevent the circuit from becoming unstable at the switching threshold, a delay and hysteresis are introduced in the circuit. The hysteresis depends on the resistance R7, since the emitters of both transistors are connected to the power minus through it, then when VT2 is opened, the voltage on R7 increases and shifts the transistor VT1 even more towards the closed state. Thus, this is a transistor Schmitt trigger. The R5-C2 circuit delays, in time, the switching of this Schmitt trigger, excluding the reaction of the photo relay to rapid changes in illumination.
The power supply is transformerless, with a parametric stabilizer on the zener diode VD1 and the reactance of the capacitor C4. Rectifier diodes VD2 and VD3.
Fixed resistors MLT-0,125 or similar imported ones. Variable resistor R3 of the SPO type, but any one, both variable and trimmer, indicated on the resistance diagram, will do.
Zener diode - any for a voltage of about 15 V. Diodes VD2 and VD3 - any for a reverse voltage of at least 400 V.
Electrolytic capacitors like Jamicon, but you can use K50-35 or any other analogues. Capacitor C4 is an imported film capacitor, designed for an alternating voltage of 275 V (AC275V), pay attention to this, since domestic capacitors of the same type, for example, K73, are marked for maximum direct voltage, so if the capacitor is domestic, then it must be at a voltage not lower than 400 V.
Transistors - any KT315 or KT3102.
When installing, you need to try so that direct light from the flashlight does not fall on the photoresistor, otherwise the circuit will not work correctly.
Author: Karavkin V.
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