Circuit design of automatic street light controller using power switch TWH875

　　Circuit working principle: The light-controlled street light circuit consists of a power supply circuit and a light-controlled circuit, as shown in the figure. The power circuit is composed of power transformer T, rectifier diodes VDl-VD4 and filter capacitor C. The light control circuit consists of photoresistor RG, resistors R1, R2, variable resistor RP, electronic switch integrated circuit IC, relay K and diode VD5. After the AC 220V voltage is stepped down by T, rectified by VD1-VD4 and filtered by C, it provides +12V working power for the light control circuit. During the day, RG is exposed to light and becomes in a low-resistance state, causing the IC's pin 2 (strobe terminal) and pin 4 (output terminal) to be at high level. Its internal electronic switch is in a cut-off state, K does not pull in, and the street light EL not bright. At night, when there is no light, the RC is in a high-resistance state. Pin 2 of the IC becomes low level, the internal electronic switch is turned on, and the EL lights up. Adjusting the resistance of RP can change the sensitivity of the light control.

　　Rl and R2 use 1/4W metal film resistors or carbon film resistors. RP uses solid variable resistors. RG uses RG45 series photoresistors. C selects an aluminum electrolytic capacitor with a withstand voltage of 16V. VDl-VD5 use 1N400l or lN4007 silicon rectifier diodes. The IC uses the TWH8751 electronic switch integrated circuit. K selects JZX-22F type (contact current load is IOA) l2V DC relay, and its two sets of normally open contacts can be used in parallel. T selects a power transformer of 3-5W and a secondary voltage of l2V. You can make your own printed circuit board during production, or you can use a universal printed circuit board. After the circuit is installed, as long as the wiring is correct, it can generally be used normally without debugging.