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    Low frequency FET response, determining f[sub]L[/sub] of Cs capacitor

    Following online book has a clue on how to find the equivalent resistance: https://books.google.com/books?id=qm9QCvyiF2MC&lpg=PA182&ots=-RQ5O9VvTR&dq=cutoff%3Dbl&pg=PA182#v=onepage&q&f=true
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    Transistors / hfe / Active region conflicts

    There is certainly a correspondence between the diode voltage and diode current. But in this case the current is the independent variable. The independent variable controls the dependent variable.
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    Transistors / hfe / Active region conflicts

    OK, so now take a similar setup with a current source in series with a resistor of some random value, an ammeter, and a diode. Crank up the current source until the ammeter reads one ampere. Does one know the voltage being supplied by the source? No. Does one know the voltage drop across the...
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    Transistors / hfe / Active region conflicts

    Yes, Vbe determines Ib if one drives the base-emitter junction with a voltage source, since that makes Vbe the independent variable and Ib dependent. But a circuit designer does not drive the base-emitter junction with a voltage source. So what importance does the original statement have for a...
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    Transistors / hfe / Active region conflicts

    If Vbe were of fundamental importance, then circuit design procedures would not assume that it is a standard value equal to one diode drop. But in fact they do exactly that, and use negative feedback so the collector current can modify (control) the base current in order to stabilize the...
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    Transistors / hfe / Active region conflicts

    Yes, I was talking about biasing a transistor, so that would be in a circuit. This is, after all, an Electronics Forum where the usual process is to put the transistor into a circuit. Nor does is really matter whether Vbe is applied directly or set indirectly by other means, in a transistor...
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    Transistors / hfe / Active region conflicts

    It's probably just too simple to understand. Ib controls Vbe, Vbe controls Ic. We design bias networks to maintain constant Ic by having Ic control Ib. Vbe is assumed to be a constant diode forward voltage drop (~0.6V), therefore its particular value is not relevant. However, when we use a...
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    Transistors / hfe / Active region conflicts

    If you have difficulty accepting the fact that Vbe controls the collector current, but that the particular value of Vbe is not relevant, then perhaps you should re-examine your understanding of transistor principles.
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    Transistors / hfe / Active region conflicts

    What seems to be your problem? It is well known that that the I-V characteristic of a diode junction is much too temperature sensitive for any particular voltage to be applied. That's why Vbe is not relevant.
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    Transistors / hfe / Active region conflicts

    You are correct. That should have said, "we never apply a voltage directly to the base-emitter junction of a transistor..."
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    Transistors / hfe / Active region conflicts

    Most common-emitter stages also employ an emitter resistor for negative voltage feedback. So in a real circuit the value of Vbe is not relevant (assumed to be a constant forward biased diode drop) nor is the value of Ib relevant (except that the high current gain of the transistor makes Ib...
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    Transistors / hfe / Active region conflicts

    That's obviously the problem right there. In BJT physics the value of Vbe is important. But in electronics we never apply a voltage directly to the base of a transistor; we apply a bias current. The value of Vbe is not relevant, except for the extents of its drift range.
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    Transistors / hfe / Active region conflicts

    But with the drift in Vbe it is possible that the same value of Vbe will lead to different values of Ic, and that different values of Vbe will lead to the same value of Ic. In fact the base current is a much better indicator of collector current because the relationship is more linear than the...
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    Transistors / hfe / Active region conflicts

    Not true. Vbe is the voltage which appears at the external base and emitter terminals. Vbe enters its useful zone only when current is forced to flow from base to emitter.
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    Transistors / hfe / Active region conflicts

    Unless the transistor base is connected to an external input, the transistor is inoperative. If the base is driven by a voltage source, then Vbe controls the base current. If the base is driven by a current source, then the current source controls the base current and Vbe adjusts itself...
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    Transistors / hfe / Active region conflicts

    I never stated that "base current from a current generator controls collector current." Whereas your statement, "Vbe does control the base current according to the physics of the transistor {#30}" is nonsense when the base is driven by a current source because the current source will increase...
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    Transistors / hfe / Active region conflicts

    What is the interest in knowing the exact value of Vbe when that value will drift?
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    Transistors / hfe / Active region conflicts

    It is just the simple realization that when the base is driven with a current source, Vbe does not control the current. It is the current source that controls the current which flows while Vbe becomes whatever value is necessary to reflect that exact current plus other drift factors. Once the...
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    Transistors / hfe / Active region conflicts

    Perhaps "irrelevant" is too strong a word, but it was chosen to emphasize disregard for the nonsense that Vbe controls the base current when the base is driven by a current source. Nevertheless, biasing networks are seldom designed as perfect current sources so that voltage drift in the...
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    Transistors / hfe / Active region conflicts

    No doubt true, but the value of Vbe is irrelevant, and the base current as set by the bias network controls the operation of the transistor in-circuit.
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