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Bipolar Junction Transistor (BJT) theory
28 questions By Tony R. Kuphaldt
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Question 28 of 28
One of the most important parameters for semiconductor components is the power rating. Explain why power rating is such a critical parameter, especially compared with other types of electronic components (resistors, inductors, capacitors, etc.).
Reveal answerSemiconductor devices tend to be especially sensitive to temperature. Thus, it is paramount to maintain power dissipation below maximum rated levels.
Challenge question: some semiconductor datasheets specify altitude values (height above sea level) along with the power ratings. Explain why altitude has anything to do with the power rating of an electronic component.
Notes:High temperature is the bane of most semiconductors. A classic example of this, though a bit dated, is the temperature sensitivity of the original germanium transistors. These devices were extremely sensitive to heat, and would fail rather quickly if allowed to overheat. Solid state design engineers had to be very careful in the techniques they used for transistor circuits to ensure their sensitive germanium transistors would not suffer from “thermal runaway” and destroy themselves.
Silicon is much more forgiving then germanium, but heat is still a problem with these devices. At the time of this writing (2004), there is promising developmental work on silicon carbide and gallium nitride transistor technology, which is able to function under much higher temperatures than silicon.
What surprises me is the following: I did not see any mentioning of the most important BJT parameter: Transconductance gm.
(Instead, you are stating that the beta-value would be a very important parameter - which is NOT the case!).
Like some other low-level electronic books and papers you treat the BJT as a cittent-controlled device - this is simply wrong.
There is not a single proof that the BJT would be a CCCS !
However, there are many theoretical explanations, measurements and observable facts which clearly show that the BJT is - of course - voltage-controlled. Who can deny it ? With which arguments? Ic=beta x Ib is just a formula - a misinterpretation of Ib=Ic/beta.