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I mean the normal working modes (cutoff, forward/reverse active, saturation).

Or an other form of the question: Do Ebers-Moll cover the whole working domain of BJT (in potential and current values)?

RobertSzili
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  • No, it doesn't. – Andy aka Oct 25 '20 at 16:32
  • The model does not take into account the inner capacities, high frequency effects, heat dependency. Besides these covers all modes? – RobertSzili Oct 25 '20 at 16:40
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    Remember this: "All models are **wrong**, some models are **useful**". It depends on what mode the transistor is in and how you want to use it if a model will give a result that can be relied upon. Also: if some model covers "everything", then why do other models exist? – Bimpelrekkie Oct 25 '20 at 16:57
  • I would not say "wrong" - models are models, which means: The are accurate enough for representing the most important and most relevant transistor properties. In this context, remember: Even no equations are 100% correct in electronics. We always have to face neglections (of 2nd order effects) and simplifications.. – LvW Oct 25 '20 at 17:08
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    Yes it does cover the four working areas you mention in DC quasi-static operations. The alphas (forward and reverse) and the saturation currents dependencies are somehow hidden, you should have a function of Ic,Vcb,temp etc. describing them. – carloc Oct 25 '20 at 17:43
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    The Ebers-Moll "model" comes in three flavors (prior to Gummel-Poon arriving.) I discuss the level-1 model [here](https://electronics.stackexchange.com/a/252199/38098). This does NOT include bulk resistance, charge storage (which are in the level 2 model), or bandwidth modulation (which appears in the level 3 model.) Gummel-Poon takes a more physically-aligned approach for bandwidth modulation and includes the so-called Late Effect, when it does so. All of these models work in all quadrants. (These are the full non-linear models and are not some simplified, "linearized" small-signal model.) – jonk Oct 25 '20 at 18:14

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From the comments and some research: Ebers-Moll is quite accurate approximation of a BJT's low frequency processes. It does not deal with delay effects coming from inner capacities. But for a low freq textbook circuit describes well the four states mentioned above.

RobertSzili
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