Problem with Amplifier Circuit

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Tutan Debnath

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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**
 

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.
 

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.
 

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