Amplification principle of triode

Amplification principle of triode

1. The launch area emits electrons to the base area

The power source Ub is applied to the emitter junction via the resistor Rb, and the emitter junction is forward biased, and the majority carriers (free electrons) in the emitter region continuously cross the emitter junction into the base region to form the emitter current Ie. At the same time, most of the carriers in the base region also diffuse to the emitter region. However, since the majority carrier concentration is much lower than the carrier concentration in the emitter region, this current can be ignored. Therefore, it can be considered that the emitter junction is mainly a electron stream.

2. Diffusion and recombination of electrons in the base region

After the electron enters the base region, it is dense near the emitter junction, and gradually forms an electron concentration difference. Under the effect of the concentration difference, the electron flow is caused to diffuse into the collector junction in the base region, and the collector electric field is pulled into the current collector. The region forms a collector current Ic. There is also a small fraction of electrons (because the base region is very thin) recombined with the holes in the base region, and the ratio of the diffused electron flow to the composite electron flow determines the amplification capability of the triode.

3. Collecting electricity in the collector area

Since the collector junction plus the reverse voltage is large, the electric field force generated by this reverse voltage will prevent the electrons in the collector region from diffusing into the base region, and at the same time, the electrons diffused to the vicinity of the collector junction are pulled into the collector region to form a collector main. Current Icn. In addition, minority carriers (holes) in the collector region also produce drift motion, which flows to the base region to form a reverse saturation current, which is represented by Icbo, which is small in value but extremely sensitive to temperature.