Problem with Amplifier Circuit

[Tutan Debnath]

Hi All,
i am trying to make an amplifier circuit(Speaker Using Transistor BD139). Now calculating Q parameters( I_CQ & V_CEQ) problem with selection of "Beta" From the datasheet I can choose it but Datasheet has the graph(hFE Vs I_C) for V_CE=2V, But my calculating V_CEQ=5.5V. So how can I choose My Beta for Design.

Here the Datasheet Link...
**broken link removed**

 

[FvM]

As a first guess, you can assume same B for 2V and 5V Vce. Type and temperature variation will be much larger (at least 2:1) than the rather small voltage dependency.

 

[rahdirs]

hfe is dependent on Ic & to some extent on VCE. So,it may be almost near to the same value at same value of Ic.
It's just a change of 3.5 V.
You can find Ic vs Vce plot in data-sheet.You have hfe vs Ic.

If you want,you could plot the graph for different values of Vce,but i don't think it would be worth it for 3V change.