555 light control timing streetlight circuit

Published:2011/5/22 5:06:00 Author:TaoXi | Keyword: light control, timing, streetlight | From:SeekIC

The step-down rectifier circuit supplies the VDD=9V DC voltage to the control circuit, the biasing circuit of VT2 is composed of the phototransistor VT1 and R1. At night, the base electrode has no light, so c-e has the high resistance, VT2, VT3 and the switch tube VT4 conduct, IC1，IC2 get the power, the astable oscillator which is composed of the IC1(555) and R5，R6，RP1，C2 starts to work. The oscillation frequency f=1.44/(RP1+R5+R6)C2. The monostable charging circuit is composed of the IC2 and RP2，C3, the time constant Rp2C3>>T=1/f. At the beginning, the voltage of C3 is lower than 1/3VDD trigger electrical level, so IC2 sets, pin-3 has the high electrical level, SCR conducts and the street lamp H turns on.



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