I feel stupid.
I, for the life of me, don't understand this stuff.
So I need a resistor on the base pin of a PNP transistor to protect it yada yada yada. I've read that a good approximation for what you should use would be to make the base current 5 times the value(or from a different site 30% more) that would just saturate the transistor. On the datasheet I just find a base-emitter and collector-emitter saturation voltage. Here's the datasheet for the pnp I'm using.
http://www.fairchildsemi.com/ds/PN%2FPN3645.pdfOk as I'm writing this I'm also researching, so I found this equation to calculate the resistor.
R1 = Supply Voltage / ( Maximum Current Required / Minimum HFE * saturation current )
The only thing I don't know is the Minimum HFE. I just don't get it. There is a bunch of Hfe ratings there, but none at 5V and 40 mA... I'm just confused....