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1  Using Arduino / LEDs and Multiplexing / Re: RGB LED voltage drop on: July 30, 2012, 08:18:54 pm
Thanks, everyone. Assume it's going to be a simple parallel circuit of 16 RGB LEDs (= 48 diodes). It has to be able to light up (but not set on fire) whether one or all of them are on at once. (Is that possible? I could potentially use a decoder).

Next question: What effect does the rating for current of the power supply have on the circuit? If it's rated at 1200 mA, but my LEDs say "maximum 20 mA", and I have only one diode on at a time, does that mean it will burn out? Or do I ignore that when designing the circuit? I only understand how to use V = IR, so I'm confused when the power supply has both a V and an I rating...
2  Using Arduino / LEDs and Multiplexing / RGB LED voltage drop on: July 29, 2012, 07:27:37 pm
I have a few basic questions. I'm thinking about ordering these: https://www.sparkfun.com/products/9264 (2nd pass made to link fixed, moderator)

First, what is forward current (20 mA for each color) vs peak forward current (30 mA)? On the datasheet they appear under "absolute maximum ratings", but I'm assuming 20 mA is what I should be aiming for?

Second, it says it has a voltage drop of 2.0, 3.2, 3.2 V respectively across R,G, & B. How do I take this into account when designing a circuit? Say I have a 5 V power supply, and want to connect 3 of these in parallel (so technically 9 total, since each RGB LED acts as 3 LEDs...?). Does it change the V=IR equation?

Assuming they should each run at 20 mA (if I understood the datasheet correctly like I asked above), does that mean the resistance within each diode would be calculated by:

red: 2 V = 0.02 * R
R = 100 ohms

green & blue (each): 3.2 V = 0.02 * R
R = 160 ohms

Finally, if that IS the case, do I need to take into account those resistance values in the circuit? So:

red: 5V = 0.02 * (R1 + 100)
R1 = 150 ohm resistor is needed

green & blue: 5V = 0.02 * (R2 + 160)
R2 = 90 ohm resistor is needed for each

Or am I totally off? Please help, so confused...
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