http://www.fairchildsemi.com/ds/MM/MMBT2222A.pdf
I think this was the datasheet I was using.
The 2n2222s are for a cube that lights upto 4 RGB LEDs, assuming they are 20ma, then that means I need between 0 and 240 ma (12x20=240) for the LEDs, but that doesnt account for dissipation by the resistors or transistors in the circuit.
From what I can tell, if I use too much base resistor, it may limit current too much. and not sink enough current, which may make it not light up enough, too small of a resistor, and you risk drawing too much current from the microcontroler.
With the mosfets, you dont seem to need that resistor, or is it just under some circumstances?
I have 2 cubes that will need mosfets for turning planes on and off (both cubes are 4x4x4 RGB, and use a 4 plane setup for a 25% duty cycle. Each plane consists of 16 RGB LEDs, assuming 20ma, that totals 16x60=960ma, or about an amp.
One cube sinks, while the other cube sources, so I picked out an n-channel, and a p-channel.
Heres a link to the n-channel.
http://www.diodes.com/datasheets/ds30830.pdf
and heres a link to the p-channel.
In post #77 I talk about how I come to think that this will be a good part, and in post 81 I list the parts that I ordered.
As I understand things, the fets wont need a gate resistor (similar to a base resistor), but it will work best if I have a gate/source resistor (makes it switch faster?). I also read about ringing, and that you can have a ringing issue that may damage the fet, the resistor reduces ringing?
When you talk about a beta, is that the same as gain, or HFE as I've read in other documents?
It was quite a bit of effort trying to figure out the right parts. I had to read a lot of datasheets and try to compare values and such. Digikeys website helped, but even then I spent hours. It would be nice if it were easier.