Phoenix redundant module 2320186 automatic current balancing

For semiconductors doped with donor impurities, the conductive carriers are mainly electrons in the conduction band, which belong to electronic conductivity and are called N-type semiconductors (Figure 3). Semiconductors doped with acceptor impurities belong to hole type conductivity and are called P-type semiconductors. Semiconductors can generate electron hole pairs at any temperature, so there may be a small number of conductive holes in N-type semiconductors and a small number of conductive electrons in P-type semiconductors, both of which are called minority carriers. Minority carriers often play an important role in various effects of semiconductor devices.

When a P-type semiconductor and an N-type semiconductor come into contact with each other, the boundary region is called a PN junction. The free holes in the P region and the free electrons in the N region need to diffuse towards each other, causing the accumulation of positive and negative charges on both sides of the PN junction, forming an electric dipole layer (Figure 4). The direction of the electric field in the electric dipole layer precisely prevents diffusion from occurring. When the diffusion effect caused by unequal carrier density reaches equilibrium with the electric field in the electric double layer, a certain potential difference is formed between the P region and the N region, which is called the contact potential difference. Due to the diffusion of holes in the P region to the N region and their recombination with electrons in the N region, and the diffusion of electrons in the N region to the P region and their recombination with holes in the P region, the number of free carriers in the electric dipole layer is reduced, forming a high resistance layer. Therefore, the electric dipole layer is also called a barrier layer, and the resistance value of the barrier layer is often tens or even hundreds of times that of the original resistance value of the semiconductor that makes up the PN junction.

PN junction has unidirectional conductivity, and semiconductor rectifiers are made using this characteristic of PN junction. Another important property of PN junction is the ability to generate electromotive force upon exposure to light, known as the photovoltaic effect, which can be used to manufacture photovoltaic cells. Semiconductor devices such as semiconductor transistors, thyristors, PN junction photosensitive devices, and light-emitting diodes all utilize the characteristics of PN junctions.

Unidirectional conductivity of PN junction

The positive pole of the power supply connected to the P terminal and the negative pole of the power supply connected to the N terminal are called PN junction positive bias. At this point, the PN junction is like a switch closed, showing a very small resistance, which is called a conducting state.

The negative terminal of the power supply connected to the P terminal and the positive terminal of the power supply connected to the N terminal are called PN junction reverse bias. At this time, the PN junction is in the off state, like a switch open. The junction resistance is very high, and when the reverse voltage increases to a certain extent, the PN junction will break down and be damaged.