(1) The diode has unidirectional conductivity

The positive electrode of the diode is connected to the high potential in the circuit, and the negative electrode is connected to the low potential, which is called positive bias (positive bias). At this time, there is a small resistance inside the diode, and a large current passes through, and this state of the diode is called the positive conduction state.

The positive electrode of the diode is connected to the low potential in the circuit, and the negative electrode is connected to the high potential, which is called reverse bias (reverse bias). At this time, the inside of the diode presents a large resistance, almost no current through, this state of the diode is called the reverse cut-off state.

(2) Positive characteristics

When the forward voltage is small, the diode presents a large resistance, basically in a cut-off state, this region is often called the "dead zone" of the forward characteristics, the general silicon diode "dead zone" voltage is about 0.5V, germanium diode is about 0.2V.

When the forward voltage exceeds the "dead" voltage, the resistance of the diode becomes very small, the diode is in the on-state, and the voltage drop at both ends remains basically unchanged after the diode is on, and the silicon diode is about 0.7V and the germanium diode is about 0.3V.

(3) Reverse characteristics

When the reverse cut-off diode is applied to the reverse voltage, there will still be reverse current flowing through the diode, which is called leakage current. The leakage current basically does not change with the reverse voltage, which is called the reverse cutoff region.

When the reverse voltage added to both ends of the diode exceeds a specified value, the reverse current suddenly increases sharply, which is called the reverse breakdown phenomenon. In practical application, ordinary diodes should avoid working in the breakdown range.