After reading this article, I finally understand the diode

After reading this article, I finally understand the diode


Diode is widely used in electronic circuit, which can protect the circuit, prolong the circuit life and so on.


Diode characteristics

Unidirectional conductivity.

Reverse characteristics:

When the applied reverse voltage does not exceed a certain range, the current through the diode is the reverse current formed by the drift motion of a few carriers, and the diode is in the cut-off state.

Electrical breakdown:

When the applied reverse voltage exceeds a certain value, the reverse current will suddenly increase. This phenomenon is called electrical breakdown. The diode loses its unidirectional conductivity during electrical breakdown.



The conducting capacity of a semiconductor lies between that of a conductor and an insulator.

An electronic material, including silicon, selenium, germanium, etc., that can be used to make semiconductor devices and integrated circuits.


N-type semiconductor

N is negative, which is a semiconductor with a high electron concentration, and its conductivity is mainly due to the conduction of free electrons.


P-type semiconductor

P is positive, which is mainly a semiconductor with positive charged hole conduction.


PN junction

When P type semiconductor and N type semiconductor are made on the same semiconductor substrate, the charge region formed at the interface is called PN junction.

PN junction has unidirectional conductivity and is widely used in electronic devices, such as semiconductor diode and bipolar transistor.

When the PN junction is applied with a forward voltage, the holes in the P region and the electrons in the N region move towards the PN junction and neutralize, making the PN junction narrow, which is equivalent to a resistance with very small resistance, that is, PN junction conduction.


Various types of diodes


Switching diode

Switching diodes are diodes designed for switching operations on circuits and are used mainly in electronic computers, pulse and switching circuits.


Rectifier diode

A rectifier diode can convert alternating current into direct current.

Rectifier diode is mainly used in a variety of low frequency half wave rectifier circuit.  


Bridge rectifier

The bridge rectifier is composed of multiple rectifier diodes.

A bridge rectifier consisting of two diodes is called a half-bridge, and a bridge rectifier consisting of four diodes is called a full bridge.

The main function is to rectify, adjust the direction of current.


Transient voltage suppression diode

Transient diode (TVS) is a kind of highly efficient protective device.

When the poles of TVS diode are affected by the reverse transient high energy impact, it can change the high impedance between the poles into low impedance at a very fast speed, absorbing surge power, protecting the precision components in the circuit from the damage of various surge pulses.

TVS is widely used in electronic circuits because of its advantages such as fast response speed, large transient power, low leakage current, small breakdown voltage deviation, easy control of clamping voltage, no damage limit and small size.



Photodiode is also known as photosensitive diode, as a light control element can be used for various object detection, photoelectric control, automatic alarm and so on.

When the light is irradiated, PN junction produces free electrons and holes in pairs , and the reverse current increases. The reverse current, which increases with the intensity of the light, converts light energy into electricity.


Light-emitting diode

Light-emitting diodes(LED), convert electrical energy into light.

There are many advantages of Led, such as low drive voltage, small working current,  strong vibration and impact resistance, small size, high reliability, low power consumption and long life.


Voltage regulator diode

Voltage regulator diode is also called Zener diode. Using PN junction reverse breakdown characteristics, while the current change in a wide range, the voltage keeps the same. This can play a role in voltage regulation.


Laser diode

Put a layer of photoactive semiconductor between the PN junction of the light-emitting diode, and its end face has a partial reflection function, thus forming a optical resonator. In the case of forward bias, the PN junction emits light and interacts with the optical resonator, thereby further stimulating the emission of single-wavelength light from the junction.

Laser diode is widely used in optical disc drive, laser printer, photoelectric equipment and so on.


Infrared remote control system

The infrared remote control system is divided into two parts: transmitting and receiving.

The emitting part is infrared LED.

The PN junction is made from a material with high infrared radiation efficiency, such as gallium arsenide so it can emit infrared light.

The most widely used infrared leds emit infrared light at around 940nm.

The receiving part is infrared receiving diode, also known as infrared photosensitive diode.

In practical application, the infrared receiver diode can work properly only when it is biased in reverse.


Varactor diode

Varactor diode, also known as variable reactance diode, is made by using the property that the junction capacitance changes with the applied voltage when PN junction is reverse-biased.

When the reverse bias voltage increases, the junction capacitance decreases, and vice versa. The capacitance of the varactor diode is usually small, its maximum value is tens of pF to hundreds of pF, and the ratio of the maximum capacitance to the minimum capacitance is about 5:1.

It is mainly used in high frequency circuits for automatic tuning, frequency modulation, phase modulation, etc., for example, as a variable capacitor in the tuning loop of a television receiver.


Bidirectional trigger diode

Bidirectional trigger diode, also known as two-terminal AC device, is commonly used to trigger bidirectional thyristor, but also can form overvoltage protection, timing, shift equal circuit.


Schottky diode

Schottky diodes are not made using the PN junction principle, but are made using the metal semiconductor junction principle, also known as metal semiconductor diodes or surface barrier diodes, which are a type of hot carrier diode.

Schottky diode uses metal, such as gold, silver, aluminum, platinum, etc., as the positive electrode and N-type semiconductor as the negative electrode.


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