Gentlemen - I was absent for 6 weeks (travelling through Bolivia/Chile) and I am a bit surprised that this funny discussion does not yet came to an end.
I am sure, we cannot convince Claude - but that´s not OUR problem.
I think, one of his fundamental misunderstandings is summarized in his sentence:
Just as Id is a f(Vd), it is also true that Vd is a f(Id). Which is the "cause vs. effect" is an endless chicken-egg vicious circle.
No - it is not a "chicken-egg question". In all the simple BJT based circuits we are discussing here it is the VOLTAGE that is the primary source only.
No currents without a driving voltage! It is simply impossible (!!) that a small current should be able to DIRECTLY control the value of a larger current.
Even if we speak of an "injected base current" - in fact, we do nothing than to use a voltage source with a large series resistor Rs , thus creating a voltage division between Rs and the B-E path.
More than that, all his simulations never can answer physical "cause-and-effect" questions. I think, this was discussed/explained sufficiently in the past.
We all know that (a) the DC collector current Ic rises as a a result of a temperature increase and (b) that a reduction of the B-E voltage of app. 2mV/K will bring Ic back to its initial value.
This value is verified by measurements as well as theoretical calculations based on carrier physics.
Question to Claude: If the base current would be the controlling quantity, shouldn`t a corresponding analysis exist showing by which amount the base current Ib has to be reduced (in mA/K)?
Do you know such a key parameter?
LvW
Is this serious? We covered this. On this forum and others, I made it clear that
emitter current is what controls collector current. Please consult a good text so you can learn that emitter current and base current are NOT the same thing. "Ib" is base current, "Ie" is emitter current. Please learn the difference. The b-e junction serves as the "input port" for the bjt, but the 2 terminals DO NOT have the same current. The "current controlled" description of the bjt refers to emitter, not base current. LvW, please believe me, I would not lie to you or anyone, Ib is NOT the same as Ie. Please learn the distinction.
I posted an excerpt from the original 1954 Ebers-Moll paper, and Ie is modeled as the control quantity. Since 1954, Ie, not Ib, has always controlled Ic. I keep re-iterating, yet you keep knocking down the base current straw man.
"No currents without a 'driving voltage'"?! I've stated ad infinitum that Vbe is NOT a "driving voltage". Vbe is a drop, not an emf. It doesn't drive anything, the power source does, i.e. microphone, antenna, CD player output, AM/FM tuner output, etc. Please note that voltage cannot exist w/o a current to displace the charges. A battery is a prime example. The electric field across the terminals is made possible by the redox reaction which propels ions against the electric field. Positive ions are forced towards the positive terminal, and likewise for negative. The current inside the battery moves against the E field.
Otherwise the E field would de-energize and the current would cease as well as the voltage.
Question to Claude: If the base current would be the controlling quantity, shouldn`t a corresponding analysis exist showing by which amount the base current Ib has to be reduced (in mA/K)?
Do you know such a key parameter?
Base current is not the controlling quantity, emitter current is. Until you learn that base and emitter currents are not the same, I can't reach you. But re temp, the Shockley diode relation, also present in Ebers-Moll relation is as follows: Id = Is*exp((Vd/Vt)-1), or likewise Vd = Vt*ln((Id/Is)+1).
The "Is" factor, reverse saturation current, or a scale current if you prefer, is a stron function of temperature. This current is spec'd in "neper-amp per degree Kelvin". As temp increases, Id increases w/ temp non-linearly, or in a power fashion. When I worked on log amps in the 90's/00's, I measured a 1N914B diode "Is" value temp coefficient at 0.12 neper/Kelvin. For every degree K (or C) the Is value increased by a factor of exp (0.12), approx.1.1275. For a 35 degree C rise, Is increased by a factor of 66.7.
The temp coefficient is semiconductors is due to increased conduction via freeing of carriers due to thermal lattice vibrations. We bias a bjt with a fixed value of dc current. Should temp rise, the silicon is more conductive since thermal energy generates more electron-hole pairs, i.e. more carriers available for conduction. But if the bjt is biased via a current source, or a voltage source plus a sufficiently large series resistor, the same current results in a lower voltage drop across the junction. This should not be hard to understand. If the bias current is 1.0 mA, and the temp is 25 C, let's say the Vbe is 0.650 volts. If temp increases to 75 C, more carriers are in the conduction band. The same 1.0 mA of bias current results in less than 0.650 volts for Vbe because less energy per charge is needed for the same current.
But we bias b-e junctions w/ fixed current, not fixed voltage. Thermal runaway takes place if we force a 0.650 volt source right across a junction. Temp increase will result in a current avalanche given in amp-neper/deg C. For a 1N914B diode junction, if Is is 10 pA at room temp of 25 C, at 75 C it is 667 pA. Junction current has a temp coefficient as well, but we seldom use it because we never bias w/ constant voltage right on a junction.
But people like me, who have designed and patented logarithmic amplifiers (United States no. 5, 670,775; 1997), refer to current temp coefficient as well as voltage. I used them both.
Regarding simulations answering cause/effect questions, I beg to differ. Sims can indicate strong relations between specific quantities as well as prove that the lagging quantity cannot cause the leading quantity. In my sims w/ diodes and inductor de-energizing, the sim clearly shows that the inductor current enters the diode first, then forward diode voltage drop develops as a result. This is when the inductor de-energizes. When the inductor is acquiring energy, diode is connected right across a constant voltage source, the input supply. Here, the diode voltage, Vd, determines the reverse current Id. It works both ways.
With the bjt, I showed that Ie clearly changes well before Vbe, and there can be no doubt that Ie is NOT controlled by Vbe. Yet Ic, the collector current responds and tracks Ie like a shadow, plateaus and settles with Ie in unison, while Vbe pokes along and eventually catches up. You claimed that Re "spoiled" the sim, skewing the relation. You asked for a sim with no resistance in base, emitter, nor collector. I did that and the sim revealed that Ie is clearly incontrol of Ic.
I also simmed with a FET, and it was beyond doubt, that Id (drain current), tracked and followed Vgs, the gate-source voltage. Although Id the drain current was way out in front od Vgs, Id t=locked on to Vgs and followed the same like a shadow. The sim was unequivocally clear that in a FET, it is Vgs that controls Id.
If my sims skew the results towards current control in the bjt case, why did they indicate voltage control in the FET case? Here is the answer:
Drum roll please ---------------------
The bjt is current controlled. The FET is voltage controlled. It's that simple.
Claude