I'm trying to do something that seemed simple at first but is proving to be complicated (shocker, right?) I want to power a super bright LED (Luxeon K2, Cool White, 350mA. It's discontinued, but the datasheet is still the first hit on Google) using a 3.7V LiPo battery from SparkFun. The instructions I have for the LED tell me to regulate the voltage with an LM317 voltage regulator.
Problem being, the LED has a forward voltage of somewhere between 2.8 and 3.4V, and the LM317 appears to eat up too much voltage to make that possible. I don't want to wire 2 batteries in series because my enclosure is pretty small, and there's no space for another battery.
So I found this charging/step-up breakout board that can bump me up to 5V. I'm extremely new to electronics and this is my first project where exact voltage/current/resistance are an issue. My question is threefold:
If I'm using the breakout board to regulate my voltage, do I even need the LM317? Or can I just use resistors to get the current to where I want it?
How can I know what the current will be when it comes out of the breakout board? The datasheet for the voltage regulator on the board seems to say I can program the output current to anything between 15 and 500mA, but I don't understand how to do it.
Am I right about needing the step-up? Or could I potentially just run this with the battery and the LM317?
I'm doing this project in order to learn, so I would prefer answers that show me how to figure this out for myself as opposed to just doing it for me.