Using BJT in Practice: A Beginner's Guide

[etf]

Hi!
I studied BJT in theory for some time and now I want to use it in practice. What are limitations of BJT in real life? What should I know in order to properly use it (I mean without damaging it) ?

 

[phinds]

That's an extraordinarily broad question and has no specific answer.

Design a specific circuit using either a PNP or an NPN transistor and THEN worry about finding a transistor that will work properly in that circuit without damage.

 

[LvW]

One of the most important things is to stabilize the selected operation point (Ic) against tolerances and, in particular, against temperature effects, which can destroy the BJT.
For this purpose, it is absolulety necessary to provide negative DC feedback - in most cases simply with an emitter resistor Re.

 

[donpacino]

Be wary of transients conditions that can occur from your source, your load, or functions of your circuit. Make sure you understand the transients your part can withstand without being destroyed.

 

[rude man]

My main advice is to design circuits where beta is not an important parameter so long as it's not too small. If you look at analyses of typical bjt-resident integrated circuits this is almost always assumed.

 

[LvW]

My main advice is to design circuits where beta is not an important parameter so long as it's not too small. If you look at analyses of typical bjt-resident integrated circuits this is almost always assumed.

Yes - the importance of beta is over-estimated in many cases. Perhaps the reason is that beta - unfortunately - is called "current gain". But that is not true - beta is no gain at all because it is not the input current but the input voltage which determines/controls the output current..
As an illustration: The same circuit with two different transistors (beta values 100 and 200, resp) and with the same bias point (for a fair comparison) will have the same voltage gain.