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For the given circuit, a statement has been given in my book, saying

It is obvious that if Vbe is increased by a small amount, both hole current from emitter region and the electron current from the base region will increase. As a consequence both Ib and Ic will increase proportionally

I believe there is a mistake and it should be rather,

electron current from the emitter region

Because BE seems to be forward biased and thus the majority carriers, that is, electrons from Emitter should increase and go into the base and further in collector.

Am I right or wrong?

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  • \$\begingroup\$ Technically, both the book and you are wrong. If the base is indeed fed by a current source, then changing the voltage source will have no effect on the base current (it's being fed by a current source, remember?). \$\endgroup\$ – WhatRoughBeast Feb 24 at 20:05
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The statement of the book is correct. When you increase the base-emitter junction voltage the electron current injected into the base (and thus the collector current) increases but also the hole current injected from the base into the emitter increases similar to an isolated pn-junction. This hole current is usually the dominant cause for the base current flowing into the base. Thus the collector current and the base current increase proportionally to each other when you increase the base emitter-voltage.

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  • \$\begingroup\$ But then wouldn't that be hole current from the base region rather than the emitter region? And why would that be more significant? Base is slimmest and least doped. While the emitter competitively thicker and more doped \$\endgroup\$ – Daksh Shah Mar 10 '17 at 16:26
  • \$\begingroup\$ That's what I said. The holes injected from the base into the emitter are the main cause for the base current. This hole current is, of course, much smaller than the electron current injected from the emitter into the base which is practically the same as the collector current. \$\endgroup\$ – freecharly Mar 10 '17 at 17:33
  • \$\begingroup\$ Hole current... that always made me laugh... Reminds me of the gardener moving a hole from one end of the garden to the other by digging a hole next to it an filling in the previous. \$\endgroup\$ – Trevor_G Mar 10 '17 at 17:49
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You can take into consideration the formula Ic=Isexp(Vbe/Vt), so obviously if Vbe rises the collector current rises, and if transistor is directly active, you can use the formula Ic=betaIb, so obviously if Ic rises, Ib also rises.

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You are correct and the book is wrong if interpreted as follows. The emitter majority carriers in an NPN BJT are electrons that are injected into the base. Holes from the base cross the b-e junction and recombine as minority carriers with electrons in the emitter just as electrons recombine as minority carriers in the base with the majority-carrier holes, resulting in base current and finite beta.

However, the book is referring to the minority carriers in both emitter and base and as such, they are holes in the emitter and electrons in the base. So both you and the book are right if each is referring to the right currents, minority or majority, in base and emitter.

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