# Why does collector current increase with base current in BJT?

The base current in the BJT is due to the recombination of holes and electrons. To neutralize the p region an electron leaves the p region. If we take it the other way round, the larger the base current the greater is the recombination, so the collector current should reduce, but $$\\beta I_c/I_b\$$ . $$\I_c=\beta I_b\$$, which shows that $$\I_b\$$ is directly proportional to $$\I_c\$$.

• Ib = Ic/beta not betaxIc – cm64 Jul 29 at 18:59
• And Ib is controlling the Ic NOT the other way around – cm64 Jul 29 at 19:07
• The collector current is controlled by the voltage on the base - it is a side-effect that base-current flows and that the ratio of base to collector current is somewhat constant. – Kevin White Jul 29 at 20:24
• Here, have a β and a ×. – Hearth Jul 30 at 1:53

First, if you study the literature, there are a lot of explanations of this, at every level. The one I liked best was the one I got in a class on solid-state quantum mechanics that was aimed at engineers, but the "earlier" ones (such as the one in the ARRL Handbook, just about any year after about 1970).

This phenomenon happens because the base is thin, and the geometry of the transistor is arranged so that the emitter is smaller than the collector. Ideally, the collector surrounds the emitter, with a thin shell of base between them.

When you put a voltage on the base (or put current into the base, which induces a voltage), this voltage causes current to flow through the base-emitter junction, pretty much as you'd expect for a diode. When there is sufficient voltage on the collector, instead of these carriers staying in the base and getting recombined, they go right through the base and into the collector.

The result of this is the BJT behavior that we know and love: you put a little bit of current into the base, and you get a lot of current going into the collector.

• Agreed on sir, but the chance of recombination increases too, which might reduce the collector current. – Mohammed Adain Jul 29 at 18:41