Forward and Reverse Characteristics of Diodes

Type of diode  

There are many types of diodes. According to the semiconductor materials used, they can be divided into germanium diodes (Ge tubes) and silicon diodes (Si tubes). According to their different uses, they can be divided into detection diodes, rectifier diodes, Zener diodes, switching diodes, etc. According to the die structure, it can be divided into point-contact diodes, surface-contact diodes and planar diodes. Point-contact diodes use a very thin metal wire to press the surface of a smooth semiconductor wafer, and a pulse current is applied to make one end of the contact wire and the wafer firmly sintered together to form a "PN junction". Because it is a point contact, only a small current (not more than tens of milliamps) is allowed to pass through, which is suitable for high-frequency small current circuits, such as radio detection.  

The "PN junction" area of the surface-contact diode is large, which allows a large current (several amperes to tens of amperes) to pass through, and is mainly used to convert alternating current into direct current. "rectifier" circuit.  Planar diode is a special silicon diode, which can not only pass a large current, but also has stable and reliable performance, and is mostly used in switching, pulse and high-frequency circuits. Conductive properties of diodes  The most important property of diodes is unidirectional conductivity. In a circuit, current can only flow in from the positive pole of the diode and out from the negative pole.

The following describes the forward and reverse characteristics of the diode.  

1. Positive properties  

In electronic circuits, connect the positive pole of the diode to the high potential end and the negative pole to the low potential end, and the diode will conduct. This connection method is called the forward direction. Bias. It must be explained that when the forward voltage applied across the diode is very small, the diode still cannot conduct, and the forward current flowing through the diode is very weak. Only when the forward voltage reaches a certain value (this value is called "threshold voltage", the germanium tube is about 0.2V, and the silicon tube is about 0.6V), the diode can be turned on directly. The voltage across the diode remains basically the same after turn-on

2. Reverse feature  

In electronic circuits, the anode of the diode is connected to the low potential end, and the cathode is connected to the high potential end. At this time, almost no current flows through the diode, and the diode is in the cut-off state. , this connection is called reverse bias. When the diode is reverse biased, there will still be a slight reverse current flowing through the diode, known as leakage current.

When the reverse voltage across the diode increases to a certain value, the reverse current will increase sharply, and the diode will lose its unidirectional conduction characteristics. This state is called the diode's breakdown.