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Fire Fly drawing
Posted: Sun Mar 06, 2016 1:45 pm
by 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
Re: Fire Fly drawing
Posted: Sun Mar 06, 2016 5:05 pm
by 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.
Re: Fire Fly drawing
Posted: Mon Mar 21, 2016 2:25 am
by computer blind
whats the point in the diode, it seems to serve no function to me.
Re: Fire Fly drawing
Posted: Tue Mar 22, 2016 12:06 pm
by 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.
Re: Fire Fly drawing
Posted: Fri Mar 25, 2016 10:18 am
by computer blind
wait. i see. its to stop the battery going to the base of the transistor.