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Light-controlled lighting using triac (2)

Source: InternetPublisher:失踪的猫 Keywords: Triac light controlled lighting trigger Updated: 2021/03/18

26.<strong>Light-controlled lighting</strong> using <strong>Triac</strong> (2).gif

VDI, VD2, Cl and C2 form a simple
capacitor step-down semi-rectified power supply. After powering on,
a DC voltage of about 12V can be obtained at both ends of C2 for the light
control circuit. VT, VD3, R2, R3 and RP
form a light control circuit. During the day, the photosensitive diode VD3 has a low resistance
when exposed to light , and the VT base potential decreases, so the VT is cut off. The thyristor VS does not get the trigger voltage and is in the off state. H does not light up. At night, VD3 has a high resistance without light exposure . The base potential of VT rises and VT is turned on, which injects a forward trigger current into vs. Therefore, vs is turned on immediately and the lamp H lights up at full voltage. Adjusting the potentiometer RP can adjust the base potential of the transistor VT, thereby adjusting the light control sensitivity.





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