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A diode is an electronic device made of semiconductor materials (silicon, selenium, germanium, etc.).

The main principle is to use the unidirectional conductivity of the PN junction to add a lead and package to the PN junction to become a diode.

Main categories:

1, point contact diode

The PN junction of point-contact diode has a small contact area and can not pass through large forward current and withstand high reverse voltage.

But its high frequency performance is good, suitable for use in high frequency detection circuit and switching circuit.

2, surface contact diode

The PN junction of the surface contact diode has a large contact area, which can pass through a larger current and withstand a higher reverse voltage,
and is suitable for use in the rectifier circuit.

3, planar diode

When planar diode is used as switching tube in pulse digital circuit, the PN junction area is small, and when it is used for high-power rectifier,
the PN junction area is large.

4. Pressure regulator

Voltage regulator is a special surface contact type semiconductor silicon diode, which has the function of stabilizing voltage.

The main difference between the regulator and the ordinary diode is that the regulator is operating in the reverse breakdown state of the PN junction.

By limiting the size of the reverse current during the manufacturing process and use, it can ensure that the regulator will not be
damaged by overheating in the reverse breakdown state.

The voltage regulator is different from the general diode, its reverse breakdown is reversible, as long as it does not exceed the allowable
value of the voltage regulator current, the PN junction will not be overheated and damaged.

When the applied reverse voltage is removed, the regulator recovers its original performance. Therefore, the voltage regulator
has good repeat breakdown characteristics.

5. Photodiode

Photodiode is also known as photosensitive diode. It has a glass window in the shell for easy access to light.

It is characterized by the fact that when light shines on its PN junction, free electrons and holes can be generated in pairs, so that the concentration
of minority carriers in the semiconductor is increased.

Under a certain reverse bias voltage, the reverse current is increased. Therefore, its reverse current increases linearly with the increase of light intensity.

When there is no light, the voltammetry characteristics of the photodiode are the same as those of ordinary diodes.

Photodiode as a light control element can be used in various object detection, photoelectric control, automatic alarm and so on.

When large area photodiodes are made, they can be used as an energy source and called photocells.

At this time, it does not need an external power supply, and can directly convert light energy into electricity.

6. Light-emitting diodes

Light-emitting Diode is a semiconductor solid display device that converts electrical energy directly into Light energy, referred to as LED(Light Emitting Diode).

Similar to ordinary diodes, leds are also made of a PN structure.

The PN junction of the LED is encapsulated in a transparent plastic shell, and the shape is square, rectangular and circular.

Led drive voltage is low, the working current is small,

It has the advantages of strong resistance to vibration and shock, small size, high reliability,
power consumption and long life, etc., and is widely used in signal indicating circuits.

Commonly used in electronic technology, digital tubes, light-emitting diodes have the opposite principle to photodiodes.

When the LED is forward-biased through the current, it emits light, which is the result of the energy released when the electron is directly recombined with the hole.

Its spectral range is relatively narrow, and its wavelength depends on the basic material used.

Main application

Electronic circuit application

The use of semiconductor diodes in the circuit can play a role in protecting the circuit and extending the life of the circuit. The development of semiconductor
diodes has made integrated circuits more optimized and has played a positive role in various fields.

Diodes play many roles in integrated circuits to maintain the normal operation of integrated circuits.

(1) Switching circuit

In digital and integrated circuits, using the unidirectional conductivity of diodes to realize the circuit on or off, this technology has been widely used.

The switching diode can protect the circuit well, prevent the circuit from being burned out because of short circuit and other problems, and can
also achieve the function of the traditional switch.

Another characteristic of switching diodes is that they switch very fast. This is the traditional switch can not match.

(2) Limiting circuit

In electronic circuits, limiting circuits are commonly used to process various signals. It is used to enable the signal to selectively transmit a
part of the signal within the preset level range.

Most diodes can be used as limiter, but there are times when a dedicated limiter diode is needed, such as when protecting a meter.

(3) Voltage regulator circuit

Zener diodes are usually used in regulated circuits,

It is a kind of junction type silicon diode made by special process. The impurity concentration of this special diode is relatively high,
the charge density in the space charge area is large, and it is easy to form a strong electric field.

When the reverse voltage at both ends of the Zener diode is increased to a certain value, the reverse current increases sharply, resulting in reverse breakdown.

(4) varactor circuit

Varactor diodes are commonly used in varactor circuits to realize automatic frequency control, tuning, frequency modulation and scanning oscillation.

Industrial product application

Led is widely used in various electronic products indicator light, optical fiber communication light source, indicators and lighting of various
instruments. Many characteristics of light-emitting diodes are unmatched by ordinary light-emitting devices,

The main features are: safety, high efficiency, environmental protection, long life, fast response, small size, solid structure.

Therefore, LED is a light source that meets the requirements of green lighting.

1, the application of electronic supplies

Led in electronic products are generally used as screen backlight or display, lighting applications.

From large LCD TVS and computer displays to media players MP3, MP4 and mobile phones, leds are used as screen backlight.

2. Applications in automobiles and large machinery

Light-emitting diodes are widely used in automobiles and large machinery.

In automobiles and large mechanical equipment, direction lights, interior lighting, mechanical equipment instrument lighting,
large headlights, turn signals, brake lights, taillights and so on all use leds.

Mainly because of the fast response and long service life of light-emitting diodes
(generally the life of light-emitting diodes is longer than that of automobiles and large machinery).

3. Application in coal mines

Compared with ordinary light-emitting devices, leds have the characteristics of high efficiency, low energy consumption, long life and
strong luminosity, so miners' lamps and underground lighting equipment use leds.

Although it is not yet fully popular, it will be widely used in the near future, and leds will replace ordinary light-emitting devices in coal mine applications.

4. Decorative lights of the city

In today's bustling commercial era, neon lights are an important symbol of urban prosperity, but there are many disadvantages of
neon lights, such as not long enough life. So replacing neon with leds has a lot of advantages,

Because light-emitting diodes compared with neon lights in addition to long life, there are energy-saving, simple drive and control,
no maintenance and other characteristics.

The replacement of neon lights by light-emitting diodes will be the inevitable result of the development of lighting equipment.