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Flash light control device composed of silicon photocell

2017-02-02 15:41  
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Flash light control device composed of silicon photocell
As shown in the figure, divider circuit is made of resistor R, optoelectronics LR, potentiometer W1 and W2. When there is no light at night, the LR resistance is higher, the pressure drop is greater, so the base input current of transistor VT1 is large, VT1 conduction, VT2 is conducted too, the base current is amplified by VT1 and VT2, a part of current is outputed by collector of VT2, and then it is coupled to the base of VT1 through capacitor C to form positive feedback, meet the oscillation condition of circuit. As the large capacity of C, the oscillation frequency is very low, the oscillation signal which has been amplified in the form of impulsive current transport to signal light ZD by VT2, then it winking. When LR is irradiated by light in the day, LR resistance decreased, so the base current from R flow to VT1 is reduced bacause of diversion, VT1 turns into cut-off, the same as VT2, ZD goes out. At this time, duing to light irradiation, the silicon photocell group produce higher voltage, and charge to battery. Ajust R, C can change the flash frequency and light off time ratio. Since W1 is in series with W2 after in parallel with LR, so adjust the resistance of potentiometer W1 and W2, can change the voltage Veb between base and emitter of VT1. General silicon tube turns on when Veb ≥ 0.6V ~ 0.7V; conversely, it cuts off, so you can according to the needs to make the lamp lighted or extinguished.