Diode classification

Diodes can be classified according to their application, manufacturing materials, manufacturing process and working principle. They can be divided into rectifier diodes, Zener diodes, detector diodes, light-emitting diodes, switching diodes and photodiodes according to their applications. According to the manufacturing materials, it is divided into Ge diode, silicon diode and gallium arsenide diode.According to the manufacturing process, it is divided into two types: point contact diode and surface contact diode. According to the working principle, it is divided into varactor diode, avalanche diode and Zener diode. The shape of the diode is different depending on the application and material. The physical shape of the common diode is shown in Figure 2-44.

(1) Rectifier diode

The function of the rectifier diode is to convert the alternating current into direct current. It works by the unidirectional conduction characteristics of the diode. The physical diagram of the rectifier diode used in THT and SMT is shown in Figure 2-45.

Rectifier diodes are mainly available in metal package and plastic package. Normally, rectifier diodes with a rated forward operating current of 1A or more will be packaged in a metal structure to facilitate heat dissipation: a plastic package with a rated forward operating current of 1A or less is used. In addition, due to the continuous improvement of manufacturing process technology, many high-power rectifier diodes are packaged in plastic.

(2) Light-emitting diode

A Light Emitting Diode (LED) is a light-emitting display component made of a semiconductor material such as gallium phosphide (GaP) that converts electrical energy into light energy. It glows when there is current inside it. The light-emitting diode is formed of a PN structure like a normal diode, and also has unidirectional conductivity. It is widely used in various electronic circuits, household appliances and instrument to be used as a power indicator or level indicator.

(3) Zener diode

The Zener diode is a special surface-contact type semiconductor silicon diode. Because it functions as a stable voltage in the circuit, it is called a Zener diode. Its shape is similar to that of a normal diode. The circuit symbol of a Zener diode is “VR”, which is a polar component whose polarity is marked on one end of the component.

(4) Photodiode,

The photodiode for THT and SMT is shown in Figure 2-49. Its important feature in the circuit is the conversion of light energy into electrical energy. In the absence of illumination, the photodiode has a large reverse resistance and a small reverse current, called a dark current. When there is illumination, the photons reach near the PN junction, creating electron-hole pairs near the PN junction. The PN junction acts as an directional motion to form a photocurrent. The stronger the illumination, the larger the photocurrent. The change of light can cause the change of the photodiode current, thereby converting the optical signal into an electrical signal. Therefore, the photodiode is also called photoelectric sensor.

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