Question about collector current for designing BJT

[Lucifre]

in the Philips data sheet for 2N2222 npn transistor there are several values of Hfe(dc current gain) given for different ic ( i am guessing it is a collector current.)
correct me if i am wrong... I always thought that dc gain is unique to the particular transistor and doesn't vary with collector current. Data sheet implies that for higher ic i will have greater Hfe. So in order to design a circuit with BJT i must determine collector current and based on that set my base current?

 

[IanP]

Re: Question about bjt

The DC gain of BJTs is not unique to anything ..
If the Hfe is important in calculations you need to have data sheet(s) of a particular transistor from its manufacturer .. this parameter, and some others, may vary from manufacturer to manufacturer and from batch to batch ..
But, don't worry, it is not important if a transistor has β ≈ 50 or 250 or more .. in most cases the relationship is direct proportional to 1/β ..

Regards,
IanP

 

[laglead]

Re: Question about bjt

I think the impact is not great.