什么是二极管？

它具有开关的特性，因此可根据施加在阳极与阴极之间的电压的方向，使电流流动或不流动。这种动作称为整流。

半导体的电导率值介于导电性良好的导体（如金属）和不易导电的绝缘体（如玻璃或橡胶）的电导率之间。例如，硅和锗都是半导体材料。
（有关半导体的更多信息，请参阅e-learning“分立半导体器件基础知识”）

分立半导体器件基础知识

作为二极管材料，使用p型和n型半导体。掺杂有硼（B）或其它电子受体原子的半导体称为p型半导体，因为其中的大部分电荷载流子为正空穴。掺杂有砷或其它电子供体原子的半导体称为n型半导体，因为其中的大部分电荷载流子为负电子。pn结二极管由p型和n型半导体组合而成。例如，通过将以高能量加速的p型（n型）掺杂剂离子注入n型（p型）半导体，生成pn结。
以这种方式形成并附带电极端头的pn结称为二极管。以这种方式形成并附带电极端子的pn结称为二极管。（图1）
二极管仅在正向偏置时才会传导电流（即当阳极比阴极更加正向偏置时）（图2）。这种只允许电流沿一个方向流动的功能称为整流。

通常二极管在反向偏置时不导通。然而，随着反向偏置电压的增大，大电流会在特定电压下突然通过二极管。此电压称为击穿电压（V_BR）。在击穿区域高于V_BR时，电压的细微变化会引起电流的大幅变化。换言之，相对于电流变化，电压变化很小。一些二极管专门利用这种恒压特性，例如齐纳二极管和瞬态电压抑制（TVS）二极管（亦称为ESD保护二极管）。
图3显示了pn结二极管的I_F-V_F曲线。

Diodes are the simplest semiconductor elements and have been used in a wide range of circuits. Some applications have been replaced by ICs, but here are some examples of where diodes are still used today.

• Rectification:
  This is the most basic circuit that utilizes the characteristic of diodes that current flows in only one direction. When an AC signal centered on GND is input, the diode turns on at a voltage level that is forward voltage (VF) higher than GND.
  Even today, full-wave rectification circuits (diode bridges) that apply this technique are used in many electronic devices.

Clipper circuits, limiter circuits:
There are forward clippers and reverse clippers in clipper circuits. One application of this is the limiter circuit. This is still used today for input protection (overvoltage protection) of ICs.

• Reverse battery protection / Reverse current protection:
  In cases where there is a possibility of accidentally connecting the polarity in reverse, such as with batteries, a diode is connected in series to the power line. Since normal pn junction diodes have a large insertion loss, Schottky barrier diodes with a small V_F are used. However, care must be taken regarding leakage current during reverse bias.

• ESD protection:
  Used by connecting between the signal line and GND of an externally exposed terminal (such as a USB terminal) into which ESD may penetrate. An ESD protection diode or Zener diode specially designed for this purpose is used.