Circuit working principle: The light control street lamp circuit is composed of a power supply circuit and a light control circuit, as shown in the figure. The power circuit is composed of a power transformer T, rectifier diodes VDl-VD4 and a filter capacitor C. The light control circuit is composed of a photoresistor RG, a resistor R1, R2, a variable resistor RP, an electronic switch integrated circuit IC, a relay K and a diode VD5. AC 220V voltage after T step-down, VDl-VD4 rectification and C filter, provide +12V working power for the light control circuit. During the day, the RG is exposed to light and is in a low-resistance state, so that the 2 pin (gate end) and 4 pin (output end) of the IC are both high, the internal electronic switch is in the off state, K is not attracted, and the street lamp EL not bright. At night, the RC has no high-impedance illumination, and the 2 pin of the IC becomes low level, and the internal electronic switch is turned on, and the EL is lit. Adjusting the resistance of the RP can change the sensitivity of the light control. 
Rl and R2 use 1/4W metal film resistors or carbon film resistors. The RP uses a solid variable resistor. RG selects the RG45 series of photoresistors. C selects an aluminum electrolytic capacitor with a withstand voltage of 16V. VDl-VD5 selects 1N400l or lN4007 silicon rectifier diode. IC selects TWH8751 type electronic switch integrated circuit. K selects JZX-22F type (contact current load is IOA) l2V DC relay, which can be used in parallel with two sets of normally open contacts. T selects 3-5W, the secondary voltage is l2V power transformer. The printed circuit board can be made by itself, or the universal printed circuit board can be used. After the circuit is installed, as long as the line is correct, it can be used normally without debugging.
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