Solar Garden Light
Make a lighting path in the garden using this simple Solar LED light. It automatically turns on in the evening and gives light in the garden. LED light turns off in the morning. You can select any colour LED like Green, White or Yellow as per the choice.
4.7 K- 1
100 K -1
10 Ohms 1 watt – 1
Diode – 1N 4007 -1
Transistor – BD 140 PNP -1
6 V, 500 mA Solar Panel – 1
4 V 1 Ah Rechargeable battery – 1
1 Watt LED with heat sink- 1
Pin assignment of BD 140 from front side is Emitter – Collector – Base
BD 140 is a PNP transistor and it conducts only when its base is grounded. In the circuit, BD 140 acts as a switch to turn off /on LED based on the presence or absence of voltage from the Solar panel. During day time, solar panel generates around 8 volts with 500 mA current. Diode D1 forward biases and battery charges. At the same time, the positive voltage from the solar panel keeps the base of BD 140 high through the 4.7K resistor. As a result transistor remains off keeping LED also off.
In the evening, voltage from solar panel drops. D1 reverse biases and the base of transistor turns low through R2. It conducts and current flows from the battery to light LED. In the morning, condition reverses and LED turns off.