I'm going to be driving a bank of 20-25 LEDs from a single output of a PIC micro. Obviously, I need a transistor, because that's going to be somewhere in the vicinity of 400 mA (the LEDs are speced at 20 mA with 3.2V of drop, which I'll get close to by using a 100 ohm resistor and a 5V power supply).
I get into trouble when I try to figure out what sort of transistor I should use for this, because I don't understand how transistors are rated. In discussions of general transistors, the 2N3904G & 2N3906G come up as good, all-around NPN & PNP transistors. How do I look at the transistor data sheet and understand that these transistors will work? What parameters do I need to pay attention to? I want to be sure the transistor can handle the load, and I want to be sure that my PIC's output can force the transistor all the way on.
I've got some familiarity with digital electronics, but when we get into the analog world I just don't have enough of a frame of reference yet.