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.