Yes, you should have a resistor to limit the 20mA for each LED (R,G,B). What is perfect for one may give too much current to another.

LED series parallel array wizard

That is a useful tool, there are many like it on the net, but most give some very wrong answers.

 

That tool does not allow me to set three different voltages per each color LED. Also, when I just give it, for example, 3V and 20 mA, it puts a resistor on the ground side of each LED. However, there is only one ground pin on the RGB LED, with room between the pin and ground for one resistor.

I could just calculate each LED separately, but then that does not help with the other two resistors fitting in.

 

As said, the wizard does not work in all situations like yours. I would use transistor drivers for the LED, or better-maybe- darlingtons like MPSA13, with, @ 4.5V, 50Ω & 240Ω. Long ago, I used a 6V lantern battery with a few diodes in series to power a 25 TTL circuit. When V fell below 5V ,moved up a diode. Just for the heck of it I scheted out your ckt with CMOS IC, 4518, 4001 & 4081[ one each], could dig it out of recycle bin if interested.

 

Bernard

I don't have much experience with transistors, but from what I'm reading on other websites, the resistors would go before the LED color leads, and the darlington would go on the ground pin. Is that correct?

Since I'm probably using somewhere between 4.5 and 6V, would there be any advantage to using CMOS? Are TTL ICs more expensive?

 

How to drive LEDs depends a lot on configuration of the LEDs. I understand that your LED has three anode leads, R, G & B, with a common cathode lead. You can use NPN emitter followers for no signal inversion to drive the anodes, or use PNPs to invert. The ICs are mostly cheap-$.20- $ 1. for either family. 'just like CMOS, or lo V version 74HCxx.

 

Okay, got it.

Since my circuit design software doesn't have MPSA13 or MPSA14, I tried the first way with MPSA10 transistors. (attached) The simulation ran just fine. However, I don't know much about the difference among the transistors. Is MPSA10 bad?

However I do have the 2N3906s. I tried putting that one together but couldn't get the simulation to run correctly. Did I do something wrong? (attached)

 

MPSA10 is PNP transistor. If you have 2N3904's, try them in place of MPSA13's. In real hardware ,the 2N3906 ckt should work. I'm short on time today.

 

The 2N3904s seem to work flawlessly. That way has three fewer transistors, too.