How does one know the minimum current that can be used to program the base current for a bjt? Is it the base cutoff spec?
I'm trying to figure out the maximum pullup resistor I can use for a npn common collector and still have relatively unity gain.
The 2N2222 datasheet hast he Base cutoff at 20nA and the Emitter cutoff 10nA.
Does this mean that if these currents are not flowing then the bjt is not going to work as intended? Either base resistor is too large and/ or emitter resistor is too large?
20nA seems a bit small? I could use a 1M ohm resistor connected to 10V which would give me 10uA to supply to the base and it would have over 500 times the necessary current to drive the base? Likewise I could use a 1M ohm emitter resistor and not have to worry about the emitter follower being cut off?What happens to an emitter follower when there is not enough base current to bring the base emitter diode into full conduction? Do we still get the emitter following the base exactly with just a smaller diode drop between them or do we lose something in the process such as gain?
Thanks