Up to now, I count 10 answers and a lot of comments. And again I have learned that the question if the BJT is voltage- or current controlled seems to be a question of religion. I am afraid, the questioner („Why do textbooks state that BJTs are current controlled“) will be confused because of so many different answers. Some are correct and some are totally wrong. Therefore, in the interest of the questioner I like to summarize and clarify the situation.

1) What I never will understand is the following phenomenon: There is not a single proof that the collector current Ic of a BJT would be controlled/determined by the base current Ib. Nevertheless, there are still some guys (even engineers!) which again and again repeat that the BJT - in their view - would be current-controlled. But they only repeat this assertion without any proof - no surprise, because there is no proof and no verification.

The only „justification“ is always the simple relation Ic=beta x Ib. But such an equation can never tell us anything about cause and effect. More than that, they forget/ignore how this equation was originally derived: Ic=alpha x Ie and Ie=Ic+Ib. Hence, Ib is just a (small) part of Ie - nothing else.

2) In contrast, there are many observable effects and ciruit properties which clearly show and proof that the BJT is voltage-controlled. I think, everybody who knows how a simple pn diode works should also recognize what a diffusion voltage is and how an external VOLTAGE can reduce the barrier effect of this fundamental property of the pn junction.

We must apply a proper VOLTAGE across the corresponding terminals to allow a current through the depletion zone. This voltage (resp. the corresponding electrical field) is the only quantity which delivers the force for the charged carrier movement, which we call current! Is there any reason that the base-emitter pn junction should behave completely different (and does NOT react upon the voltage) ?

Upon request I can list at least 10 effects and circuit properties which can be explained solely with voltage control. Why are these observations so often ignored?

3) The questioner has presented a circuit which deserves an additional comment. We know that an opamp (undoubtly voltage driven) can be wired as a current-in-voltage-out amplifier (transresistance amplifier). That means: We always have to distinguish between the properties of the „naked“ amplifier unit and a complete circuit with additional parts.

For the present case, that means: The BJT as a stand-alone part is voltage-driven - however, viewing the whole circuit (with a resistor R1) we can treat the complete arrangement as current driven circuit if R1 is much larger than the input resistance of the B-E path. In this case, we have a voltage divider driven by the voltage Vin.

Up to now, I count 10 answers and a lot of comments. And again I have learned that the question if the BJT is voltage- or current controlled seems to be a question of religion. I am afraid, the questioner („Why do textbooks state that BJTs are current controlled“) will be confused because of so many different answers. Some are correct and some are totally wrong. Therefore, in the interest of the questioner I like to summarize and clarify the situation.

1) What I never will understand is the following phenomenon: There is not a single proof that the collector current Ic of a BJT would be controlled/determined by the base current Ib. Nevertheless, there are still some guys (even engineers!) which again and again repeat that the BJT - in their view - would be current-controlled. But they only repeat this assertion without any proof - no surprise, because there is no proof and no verification.

The only „justification“ is always the simple relation Ic=beta x Ib. But such an equation can never tell us anything about cause and effect. More than that, they forget/ignore how this equation was originally derived: Ic=alpha x Ie and Ie=Ic+Ib. Hence, Ib is just a (small) part of Ie - nothing else. (Barrie Gilbert: The base current is just a "defect").

2) In contrast, there are many observable effects and ciruit properties which clearly show and proof that the BJT is voltage-controlled. I think, everybody who knows how a simple pn diode works should also recognize what a diffusion voltage is and how an external VOLTAGE can reduce the barrier effect of this fundamental property of the pn junction.

We must apply a proper VOLTAGE across the corresponding terminals to allow a current through the depletion zone. This voltage (resp. the corresponding electrical field) is the only quantity which delivers the force for the charged carrier movement, which we call current! Is there any reason that the base-emitter pn junction should behave completely different (and does NOT react upon the voltage) ?

Upon request I can list at least 10 effects and circuit properties which can be explained solely with voltage control. Why are these observations so often ignored?

3) The questioner has presented a circuit which deserves an additional comment. We know that an opamp (undoubtly voltage driven) can be wired as a current-in-voltage-out amplifier (transresistance amplifier). That means: We always have to distinguish between the properties of the „naked“ amplifier unit and a complete circuit with additional parts.

For the present case, that means: The BJT as a stand-alone part is voltage-driven - however, viewing the whole circuit (with a resistor R1) we can treat the complete arrangement as current driven circuit if R1 is much larger than the input resistance of the B-E path. In this case, we have a voltage divider driven by the voltage Vin.