Solar flasher principle circuit

 　　As shown in the figure, the resistor R, the photoelectric element LR, and the potentiometers W1 and W2 form a voltage dividing circuit . When there is no light at night, the resistance value of LR is high, and the voltage drop on it is large, so the base current input to the transistor VT1 is large, VT1 turns on, and VT2 also turns on, and the base current passes through After VT1 and VT2 are amplified, part of the collector output of VT2 is coupled to the base of VT1 through the capacitor C to form positive feedback, which satisfies the oscillation conditions of the circuit . Since the capacity of C is large, the oscillation frequency is very low. VT2 transmits the amplified oscillation signal to the signal lamp ZD in the form of pulse current, and it emits light flashingly. When light shines on LR during the day, the internal resistance of LR decreases, so the base current flowing into VT1 through R is greatly reduced due to shunting, causing VT1 to change from conduction to cutoff. At the same time, VT2 also cuts off, and ZD goes out. At this time, the silicon photovoltaic battery pack generates a higher voltage due to light irradiation and charges the battery. Adjusting R and C can change the flash frequency and on-off time ratio. Since W1 is connected in parallel with LR and then in series with W2, adjusting the resistance of the potentiometers W1 and W2 can change the voltage Veb between the base and emitter of VT1. Generally, the silicon tube is at Veb ≥ 0.6V~0.7V When it is on, it is on; when it is on, it is off, so the lamp can be ignited or extinguished as needed.

　　Component selection: Two types of silicon photovoltaic cells, 2CR or 2DR, can be used for solar cells. LR can choose domestic 625-A cadmium sulfide photoresistor. The resistance value of this photoresistor is less than 50kΩ when there is light, and the resistance value is greater than 50MΩ when there is no light. The diode VD prevents the battery current from flowing back to the solar cell when there is no light or very weak light (the voltage of the solar cell is lower than the battery voltage) . Generally, the maximum operating current of VD is greater than the maximum output current of the solar cell group, and the reverse withstand voltage is higher than the battery voltage. If the c and b poles of 3AX31 or 3AX81 low-frequency tubes are used instead, the requirements can be easily met. R is determined during adjustment, and a small (1/8)W fixed resistor of about 47kΩ is generally used. ZD is a 2.5V, 0.3A small incandescent lamp. Other components are shown in the figure.