I'm trying to use BJT's but want to run varying currents through it. On the the data sheet for the transistor it gives the Beta value and it changes with different collector currents. My question is if there is a range of currents running through the transistor, what should I choose as my Beta value, so I can calculate my base resistor?

 

My question is if there is a range of currents running through the transistor, what should I choose as my Beta value, so I can calculate my base resistor?

What does the circuit do?

In addition to beta varying with current, among other things, it will vary from transistor to transistor. Circuit designers generally design circuits to function with a range of betas and instead depend on a minimum beta; versus typical or maximum.

 

From your description I am imagining you are not using the BJT to vary this current, instead, the current is controlled via a seperate part of the circuit while the BJT in question acts as a switch?

If so, why not pick a minimum beta and maximum current condition and set your base current accordingly?

 

My question is if there is a range of currents running through the transistor, what should I choose as my Beta value, so I can calculate my base resistor?

Choose the specified minimum value of beta at any collector current in your range of interest, calculate the maximum required base current from that value of beta, and calculate a resistor value that will give you at least that much base current, plus a bit extra for a margin of safety.