I am trying to select a transistor part and figure the actual current calculations in my circuit.
I have 30mA of collector (load current). This is the transistor I am choosing for my design : https://www.onsemi.com/pub/Collateral/MMBTA05LT1-D.PDF
So, Once I have figured out the collector current through my transistor, I need to calculate my required base current. But while calculating the required base current, how will I choose the Hfe value? In the datasheet it is given as 100 (For Ic=100mA and Vce=1.0V)
The graph in fig 5, gives Ic vs Hfe, but the Vce is 1.0V. And in fig 6, Ic vs Vce(sat), the gain is fixed as 10. How will I take values from this graph when the conditions are different from my application.
My actual Ic is just 30mA. How will I fix my gain now?
I am going to operate the transistor in linear region. It would really help me if one could tell me which graphs we need to consider in the transistor datasheet for my current calculations.
And I am calculating Min, typ and max current values for my circuit. So, I am considering -40,+25 and +85degC temperatures. Can someone help me with the calculations.