I am struggling with the calculations of the current limiting resistor for my circuit so I wanna ask you guys for help. I've tried doing this calculations on online calculators and by myself with math but the results i get are all different from different sources.
I have 9x 1W green LED's which I want to drive using 12V 2A switching power supply but by my lame beginner electronics calculations that's not enough it seems and this is why I need your help too.
This is the scheme I am trying to figure out:
Most of my calculations are suggesting that for R1 I need to use 3,9ohm 5W resistor.
As noted on the image each LED should be supplied with 3V 300mA. I read many different resistor calculations but I cant figure out the right way for my circuit since I don't really know many things in electronics.
I would appreciate if any of you could provide explanation how to calculate such circuit and help me out, or if you have any better idea of how I should build this thing. I will make a video about my build and post it on YouTube and I will make sure to mention all of you.
Best Answer
I would not use one resistor for all LED branches. Use one resistor for each LED branch.
simulate this circuit – Schematic created using CircuitLab
Uled=3V
Iled=300mA
Uledbranch=9V
Iledbranch=300mA
Vcc=12V
R= 12-9 / 3e-1 = 10 Ohms
Pr= 12-9 * 3e-1 = 0.9W
Your 12V 2A switching power supply has required current output for driving 3x300mA branches. It might flicker or get hot.
You should also try experiment with connecting 4 LEDs in series and limit the current with resistor (it will be much cheaper and smaller).