and im looking for what would be the appropriate current to apply to the base to make the transistor act as a switch (ie 5 volts in the collector, emitter through a resistor and led and then ground, and the base). i want simply 5 volts to go through. Do i look for "peak base current" under "limiting values" or IBon which is in the bottom row of quick reference data.
is there not usually a graph that tells you "if you apply 'X' much base current, with value 'Y' collector voltage, that some amount will be output"
True, there is usually that graph, but for a switching transistor we look at the saturation endpoints.
It seems that in switching mode the characteristics are more or less
I_BE ( base burrent) 15mA gives I_Con ( collector current) trough the diode of 150mA, and I_BE = 50 gives I_Con = 500.
So, roughly, in saturation you get a 10x current amplification.
But then all the load regulation, and power dissipation is on the transistor. A series resistor between Vcc and LED , current limiting, can take some heat of the transistor.
The series resistor should take up the extra voltage between LED forward voltage+ V_CE(min) transistor at the required operating current.
Yes, this is a bit complicated, but trial and error starting at reasonably low values for I_BE and using inexpensive transistors usually works well.
In switching applications your collector current is often limited by the load. You can supply as much base current as you want but it will not result in additional collector current. You do drive the transistor harder into saturation, but the only draw back is an increase in switching time. A forced beta of 10-20 is a good rule of thumb for GP transistors.