Hi all and thank you for taking your time and looking in!
I need some help in setup I have. Don't want to bore anyone with detail of why and where. I will just go into the basic facts:
a.) LED: I have 4 x LEDs (all identical). All details can be found here: http://www.led-tech.de/en/Light-Emit...1026_1_86.html
Most important (relevant specs are): 100mA, V_typ:3.4V (forward voltage I think??), V max: 4V, , 0.34W.
b.) Source: I have a battery pack of 8 x 18650 (3400mAh Panasonic) cells in 2S4P configuration so output = 8.4V~5.5V (that is full charge to cutoff range) Avg: 7.4V (your typical bike light packs).
And yes, you guessed it. I would like to drive a.) with b.). with preferable to most optimal (as in least waist of power) way possible.
To quickly get some obvious questions out of the picture. I mean like "why 2S4P? why not 1S8P? on the battery". Well the answer is simple. I have Consumer bike light (actually 2 of them) that need the 7.4V source (they have the usual control and protection circuit built-in). So the 2S setup is needed. Take it as a given.
QUESTIONS:
What I need help with is sorting out the connection and regulations. I know the basics of parallel vs serial LED connection. Yet I still managed to complete confuse myself when I started considering the following:
Should I go for 2S2P with the LEDs to get the setup closer to the source? Or is that a stupid idea? What connection (serial or parallel or hybrid) is most recommended in my case, especially taking the question below into considerations (regulator options)?
I want to use a controller but not sure which one. Please look at some of my options here: http://www.led-tech.de/en/LED-Contro...c_118_119.html
(the LEDs I already have, but controller is an open question, so I can order from ebay if you have a better suggestion or non of those fit my actual needs).
I really don't want to use resistor. I see BUCKs are much more expensive than the Mini Constant Current Power Supply (not pretending that I know what the real difference is:sssh:), but if you say I am better of with a BUCK then I will get that.
And finally allow a very stupid question: Those the fact that I have other things (the above mentioned consumer bike light) hooked up to the same source (obviously parallel) make any difference in the solution? That is choice in regulator and LED wiring. I say stupid question because I know that the answer is NO, however I have gotten myself so confused in the mini project that I am not sure anymore.
PS: I am not lazy and asking anyone to help me lookup the right regulator for me on ebay. What I need help with is the wiring recommendation and the spec calculations.
Options I came up with so far (please let me know if I am wrong or right):
1. Buy 4 x this: http://www.led-tech.de/en/LED-Contro...0_118_119.html and 1 connect to each led. Then parallel them all to the source.
or
2. Connect 2 LED in series and 2 in parallel and find a Step Down BUCK with 200mA output, 5V-9V input. Haven't been able find one, only circuit diagram: http://designs.digikey.com/library/4...4294959898/163
or
3. Connect all 4 LEDs in parallel and same as No.2 only 100mA output. Still looking for actual product, but would be something like this I guess: http://www.linear.com/product/LTC3631
(if all 3 is correct, then which should I do, which is most efficient and viable?)
Thank you very much in advance.