Ok so maybe I should do a simple constant current circuit like this:
http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/ - skip to step 6
That would provide a constant current to the LEDs, right? Or one thing he said is that this circuit has a low drop out and the power source could be as low as .6v higher than the output voltage. So does that mean if we set it up to put out 3.4v to the LEDs then once the battery drops down to 4 volts then the circuit won't work anymore?
He talks about hi power LEDs but also mentions that this circuit can be applied to regular LEDs in series or parallel.
Also, here is a stupid question for you. If you connect LEDs in parallel then they each require 20mA of current so if I use 12 LEDs then that is 240mA total. Say this is on a 4.2 v power source. Now compare that to connecting 3 of them in series so there will be 4 rows in parallel which means that the LED array will be using 80mA total. This would have to be connected to a power source greater than 10.2v. So I am correct in thinking that the LEDs connected in series will be feeding off of the same current therefore this LED array will be using less power than the LEDs connected in parallel? So if that is the case then the same battery would last 3 times longer. Is that right?
Ok so what about if I use a voltage booster to bring the voltage on the 3.7v battery up to 11 or 12 volts. How does that work? Will the battery still last 3 times longer or does one action cancel out the other and would result in the battery still being drained as fast as the LEDs connected in parallel?
It kind of sounds like regardless of whether or not I connect the LEDs in series or parallel I will need to boost the voltage on the battery (if for a parallel array boost to 6v? and for a series array boost to 12v?) Then it wouldn't matter as much as the voltage drops, right?
So how about these options:
http://www.reuk.co.uk/DC-Voltage-Multiplier-Circuit-Plans.htm
http://chemelec.com/Projects/Voltage-Boost/LT1372.htm
At first glance I don't really understand how these work so I will have to do some more research but on the first link it shows the MAX756 chip that boosts the voltage but why do you have to have the capacitors and power inductors? What functions do they serve... I am only asking in the intrest of saving space. I think this design is getting to be too complicated, not in the sense that I can't understand it, but rather I am concerned that there will be too many components and that it will not all fit in the limited amount of space. I can't add another layer of depth so we are looking at just the space that is left on either side of the battery which is only about 5 or 6mm tall. So this LED array may not have enough space to make it as efficient as possible. I would like to make it as efficient as possible in the amount of space that is available.
So I have been asking some specific questions and I am curious about the answers but I may not be able to implement them. To get kind of a final solution I would ask you, if this were your project how would you set it up using 10 - 12 LEDs, the mobile phone battery (unless you have a better option), and the ability to connect it to a usb port for charging/continuous run time? To help you I am going to make a little schematic drawing of the arc so that you understand the space limits a little better. I will post it soon