A diode is an electronic device made of semiconductor materials, consisting of a PN junction, external leads, and a shell packaging, with the written symbol VD. A diode has two electrodes, the electrode led out from the P region is called the anode (positive electrode), and the electrode led out from the N region is called the cathode (negative electrode); Due to the unidirectional conductivity of the PN junction, the current direction when the diode conducts is from the anode to the cathode through the inside of the tube.

The main principle of a diode is to utilize the unidirectional conductivity of the PN junction. Its essence is that under the action of an applied forward voltage, the holes in the P region and the electrons in the N region are continuously diffusing and moving. The two continuously neutralize the positive and negative ions at the PN junction, thereby narrowing the range of the PN junction and ultimately conducting.

As the most fundamental discrete device, diodes are useful in almost all electronic circuits. The unidirectional conductivity of diodes can play a role in various scenarios such as switching circuits, protection circuits, and voltage stabilizing circuits. With the continuous updating and development of demand, diodes themselves have also developed various forms. The following are more than ten common and commonly used circuit diagram representations of diodes:

With the continuous miniaturization of transistor processes, we are able to integrate more basic structures on smaller chip areas. Taking our current product as an example, from the structural diagram of this LM158 operational amplifier, we can see basic structures such as diodes, transistors, resistors, etc. Electronic engineers can understand the specific structure and working principle of the product through this diagram, and then use it reasonably.

Below picture is from ST brand LM158 datasheet.

Diodes, as important discrete devices, can be found in various circuits. In integrated circuits, it is also an important basic structure. The IC industry has developed to this day, and diodes can be found in various types of integrated circuit structures. Understanding diodes helps us to have a deeper understanding of integrated circuits, starting from the most basic structural hierarchy and mastering the working principles of various devices.

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