The most important characteristic of a diode is its unidirectional conductivity. In the circuit, current can only flow from the positive pole of the diode and the negative pole flows out. The forward and reverse characteristics of the diode are illustrated by simple experiments.

1, forward characteristics

In the electronic circuit, the positive pole of the diode is connected to the high potential end, the negative pole is connected to the low potential end, and the diode is turned on. This connection method is called forward biasing. It must be stated that when the forward voltage applied across the diode is small, the diode is still not conducting, and the forward current flowing through the diode is very weak. Only when the forward voltage reaches a certain value (this value is called "gate voltage", also known as "dead zone voltage", the xenon tube is about 0.1V, and the silicon tube is about 0.5V), the diode can be turned on. The voltage across the diode remains essentially constant after conduction (the transistor is approximately 0.3V and the silicon tube is approximately 0.7V) and is referred to as the "forward voltage drop" of the diode.

2, reverse characteristics

In the electronic circuit, the positive pole of the diode is connected to the low potential end, and the negative pole is connected to the high potential end. At this time, almost no current flows in the diode, and the diode is in an off state. This connection method is called reverse bias. When the diode is reverse biased, there is still a weak reverse current flowing through the diode, called the 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 diode breakdown.