This portable solar
lantern circuit uses 6 volt/5 watt solar panels are now widely
available. With the help of such a photo-voltaic panel we can construct
an economical, simple but efficient and truly portable solar lantern
unit. Next important component required is a high power (1watt) white LED module.
When solar panel is well exposed to sunlight, about 9 volt dc
available from the panel can be used to recharge a 4.8 volt /600 mAh
rated Ni-Cd batterypack. Here red LED (D2)
functions as a charging process indicator with the help of resistor R1.
Resistor R2 regulates the charging current flow to near 150mA.
Assuming a 4-5 hour sunlit day, the solar panel (150mA current set
by the charge controller resistor R2) will pump about 600 – 750 mAh into
the battery pack. When power switch S1 is turned on, dc supply from the
Ni-Cd battery pack is extended to the white LED (D3). Resistor R3 determines the LED current. Capacitor C1 works as a buffer.
Note: After construction, slightly change the values of R1,R2 and R3 up/down by trial&error; method, if necessary.