![]() Look at any datasheet, you'll see that characteristic flattening off of the characteristic curves. ![]() Yes, modern MOSFETs are fundamentally no different, and will pinch-off if you have a small gate voltage / large current. ![]() So, if your transistor is in a common emitter, non cascoded amplifier, with a collector load and the base driven by, say, 330 ohms, you could say that at DC it is mostly voltage driven, but at AC it is current driven (current through base resistor will be used mostly to drive Cbc through Miller effect, and what remains is the actual base current). Of course, on top of that, the various capacitances inside the transistor all require current (ie, dQ/dt) if we want to process AC signals when the collector moves, the current through Cbc will add or substract to the base current and introduce a HF pole. If the base is driven by a high impedance (current source, collector of another transistor, etc), then Vbe will set itself depending on the current that is injected in the base, and you could say that the current causes a Vbe voltage. In this case, Vbe matters, so the design may have to consider its dispertion and temperature drift. If the base is driven by a low impedance (ie, a voltage source), that will provide whatever base current is necessary, then it is voltage driven, and you can consider that the Vbe causes a base current (and obviously a collector current as the transistor does its job as a follower). I guess that would depend on yow you use that transistor. Do you still think that I must " stop and research the physics more" deeply - unless you can answer my questions above? Regards LvW Do you need references? 3.) Questions: * Can you explain, for example, the function of the simple current mirror without using the voltage-control principle? * Can you explain Barry Gilberts famous principle of "translinear circuits" with the current-control approach? * How do you explain the effect of negative feedback caused by an emitter resistance ? * And finally: Do you agree that Re feedback does increase the resulting input resistance of an emitter stage? And - from feedback theory we all know that such an increase is connected with current-controlled voltage feedback only (current feedback reduces the input resistance). 2.) To mention only three "witnesses" who are supporting voltage-control : (a) William Shockley (doctoral thesis), (b) Barry Gilbert (I suppose you know his name) and (c) Winfield Hill (co-author "Art of electronics"). (By the way: Even from the energy point of view it is impossible that a smaller quantity can have direct control over a larger quantity of the same kind.) You can believe me - I do not write such a comment without knowing what I am speaking about. But - from the physical point of view it is NOT the current Ib that "controls" Ic. ![]() To make it clear - of course, I do not deny the fact that there is a base current and that it must be included in the design steps. Hence, I am not surprised - on the other hand, it is surprising that such a false explanation of the BJT`s physical working principle could survive in some heads over the years. The forward and return currents travel simultaneous as a result of the fields!ฤก.) I am aware that many people rely on the current-control approach for BJT`s. This thinking is the same that teaches current "flows" from one side of a source through a circuit back to the other side. Yes, there is a minimum vBe require in your source but that is not a separable concept the current control. However, it is the current mobility here that allows current mobility in the collector loop. Yes, vBe is a net effect of current mobility in the base loop. One of Einstein's (very significant) contributions to the theory was showing that they were the *same* field viewed from different (orthogonal) relativistic reference frames. You cannot separate potential from current just as you cannot separate Electric Field from Magentic Field. Circuit theory is approximation to Field Theory. One simply cannot happen without the other. The problem is that you are applying "circuit" theory in a manner that separates current from potential. ![]()
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