For a NPN, you need to make the collector more positive than the base so the electrons emitted from the emitter will pass through the base and get attracted and injected into the collector. This positive voltage on the collector makes it reversed biased, but it needs to be that way, otherwise the transistor will not operate in the active region.
Because reverse biased junction act very similar to the current source.
What does the reverse diode current of a photodiode have to do with the need to reverse bias the base-collector of a BJT so as to keep it in the active region?
The above certainly shows that the Ib is an indicator of what the Ic will be, but it doesn't do anything to explain why the base-collector of a BJT must be reverse biased to keep it in the active region.
Hmm, I don't see any parallel at all. The first way you mentioned was direct injection. The second way was to break apart bonds within the semiconductor to create charge carriers. Two different mechanisms.
Yes, I was aware that radiation (light and x-rays) besides heat can cause bonds to break and release charge carriers.
Then they failed, because gain depends on the configuration and the external components. For instance, a common collector configuration has a gain of less than 1.
Yes, that is true.
The pn junction does not give the collector the properties of a current source. If you could injected majority carrier electrons from a external source into a single slab of N-type semiconductor material, and connect a voltage to each end of the slab, you would have a current source. That is because the current depends on the injected electrons, not on the voltage applied to N-type material. The P-type material of the base is next to the collector because it is geometrically necessary to be there to collect the electrons injected from the emitter-base junction. So is is wrong to compare the base-collector of a transistor to a regular diode. For that and other reasons, you cannot make a transistor with 2 diodes connected back to back.
It is an example of any BJT, whose collector acts as a current source for the reason given above, not because it is a reversed PN junction.
The current is regulated by changing Vbe.
You mean the emitter ejects majority carriers (electrons for the emitter) through the base and into the collector where the positive voltage attacts them into the external voltage source. The small base current is a unfortunate side effect of the Vbe necessary to lower the junction barrier voltage so the emitter can send out electrons. This base current is proportional to the current injected into the collector, and is useful for modeling and calculation purposes.
may work nicely as a model, but there are also other models. From where most of us stand, base current is the active and immediate control agency.
He would be wrong.
Actually, the assumption of base current controlling collector current works much better in a model because of its linearity. But, as I pointed out before, a model does not necessary show what is actually happening.
It is not abstruse to point out what is really happening in a BJT.
Not the control describing the physics of the BJT. There is no way to change that.
It is obviously, that it is impossible.
And for this, maybe you can read this book
I agree, that is certainly true.
You are repeating the same statement you made before, so I will repeat and rephrase my answer. The current source property of the collector does not depend on a PN junction, or the fact that the junction happens to be reversed biased. I showed that a single N-type semiconductor slab with a voltage across it could act as a current sourse if it was injected with electrons by some kind of electron gun. That was because the electron gun controls the current, and the voltage across the N-type semiconductor slab does not. I also pointed out that a positive voltage was needed to attract the electrons from the emitter, and that the position of the collector was geometrically necessary to be in the path of the emitted electrons. It is only conincidental that the collector forms a PN junction with the base, and it is reversed biased with respect to the base. If you disagree with the above discourse, please tell me where and why, but it does not do any good to repeat what you said before. I do understand what you said, and have evaluated it.
