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, isolation diodes, Schottky diodes, light-emitting diodes, silicon power switching diodes, rotating 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, and it 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 in the "rectifier" circuit that converts alternating current into direct current. 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.

 

The light-emitting diode is also composed of a PN structure and has unidirectional conductivity. However, its forward working voltage (turn-on voltage) is higher than that of ordinary diodes, about 1 to 2.5V, and its reverse breakdown voltage is lower than that of ordinary diodes, about 5V. When the forward current reaches about 1mA, it starts to emit light, and the luminous intensity is approximately proportional to the working current; but when the working current reaches a certain value, the luminous intensity gradually tends to be saturated, which has a nonlinear relationship with the working current. Generally, the forward working current of small light-emitting diodes is 10-20mA, and the maximum forward working current is 30-50mA.

 

The shape of the light-emitting diode can be made into various shapes such as rectangle, circle, glyph, symbol, etc., and there are many colors such as red, green, yellow, orange, infrared, etc. It has the characteristics of small size, low power consumption, easy driving, high light efficiency, uniform and stable light emission, fast response speed and long life, and is widely used in indicator lights and large-screen display devices.