Fire Fly drawing

[spike1947]

Hi

I am attaching a drawing for a flickering LED solar charged , I am wanting to change the supply voltage to 2.4v ( from 2 x 1.2v Ni-MH ) and using 2 x solar panels from the pound shop ( giving out 5.6v ! ) , driving a flickering LED 1.8v to 2.2v .

What would I have to change to obtain my result ! .

cheers

spike

[Sock Puppet]

Looks like it's been done (half way down this webpage) : http://www.evilmadscientist.com/2008/si ... -circuits/

A Schottky diode would work well in there.

[computer blind]

whats the point in the diode, it seems to serve no function to me.

[David]

The diode is essential. In the day, the solar cells charge the battery through the forward-biased diode. The PNP transistor's base is positive to its emitter, and the transistor is cut off. At night, the voltage of the solar cells falls below the battery voltage, and the voltage on the transistor's base drops towards zero also. The diode is reverse-biased, and the emitter voltage is held up by the battery. The transistor turns on, thus lighting the LED.

[computer blind]

wait. i see. its to stop the battery going to the base of the transistor.