I've been searching and reading what I can find on the Internet, and I've come up with:
The first page talks about using the hfe to calculate how much base current is required to supply a specific collector-emitter current.
My example is 260mA and 100hfe. According to the first page, you would take 260ma/100hfe and end up with 2.6ma to which you add 30% to come up with 3.38mA.
The second page had an interesting statement:
A resistor RB is required to limit the current flowing into the base of the transistor and prevent it being damaged. However, RB must be sufficiently low to ensure that the transistor is thoroughly saturated to prevent it overheating, this is particularly important if the transistor is switching a large current (> 100mA). A safe rule is to make the base current IB about five times larger than the value which should just saturate the transistor.
They are saying that it needs to be oversized by a factor of 5 to prevent it from overheating. I don't really understand this because as long as the Ic is below the transistor max, why would it overheat from the base current not being large enough? Wouldn't the base current not being large enough just cause a lesser Ic ?
Then, I've read that a factor of 10 should be used for saturation...
Help me out here guys!!!