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What is a diode? 

-- The latest guide for 2022

  • 1.0 What is a diode?
  • 1.1 Diode Symbol
  • 1.2 Types of diodes
  • 1.3 Characteristics of Diode
  • 1.4 Diode test
  • 1.5 Diode Applications

In this tutorial, we will explain what is a diode, its types, diode symbol, characteristics, diode test, and its applications.

1.0 What is a diode?

A diode is an electronic device made up of semiconductor materials that allow the current to flow through the circuit by closing it in one direction. The diode does not allow the current to flow in reverse or any other direction. Diodes are mostly made from these semiconductor materials:
a). Silicon
b). Germanium
Direct current can be obtained from the alternating current by the diode, which is the reason diode is also called a rectifier. Current and voltage ratings are the two main factors on the basis of which diodes are categorized. A diode has two leads, positive lead (anode) and negative lead (cathode), due to which a diode has a polarity on it. When the positive terminal of the battery is connected to the anode, then the diode allows the current to flow. Below is the attached picture, showing different types of diodes that are available in the market. Different configurations of the diode that are available in the market are shown in the attached picture. If we start from the left side, then the first one is the metal case diode, 2nd one is the stud mount diode, the middle one is the plastic case with band diode, 2nd last is the plastic case with the chamber diode and the last one is the glass case diode.

1.1 Diode Symbol 

A simple diagram is given in front to understand the diode’s symbols. A diode has one positive terminal and another negative terminal. The arrowhead type terminal is the positive one known as anode, while the other is the negative one known as cathode. The arrowhead shows the direction of the current that flows from the positive terminal and ends on the negative terminal when the diode is connected as forward-biased. The flow of electrons in the diode is opposite to the arrow sign.

1.2 Types of diodes

Following are the important types of diodes that are available in the market, every diode has its own applications. The important ones are listed below:
1.Light Emitting Diode
2.Laser diode
3.Avalanche diode
4.Zener diode
5.Schottky diode
6.Photodiode
7.PN junction diode
Various types of diodes diagram and their notation are shown in the attached picture. The most common and widely used diode type is the PN junction diode, which we are going to explain a bit before moving on. 

P-N Junction Diode 

This diode type consists of two portions of the semiconductor materials. One portion of the semiconductor is interfered with the P-type material, while the remaining portion of the semiconductor interferes with the N-type material. When these two doped portions of semiconductor join, they form a diode, known as P-N junction diode. This diode does a rectification process, which is the reason also known as rectifier diode. The diode will force the current to flow only in one direction while blocking the current from flowing in any other direction.

1.3 Characteristics Of Diode

Following are the important characteristics of diode:
1.Forward-biased diode
2.Reverse-biased diode
3.Zero biased diode

Forward-biased diode

In the forward biased connection, a normal diode will allow the current to flow through the circuit by closing it in one direction. In this scenario, the voltage difference across the forward-biased connections is less. This difference is about 700Millivolts for the silicon diode, while for the germanium diode the difference is about 290 Millivolts. In this scenario, potential energy across the arrowhead terminal is positive, while on the other terminal potential energy is negative. 

Reverse-biased Diode

A reverse-biased diode does not allow the current to pass through it by behaving just like the insulator. The reverse voltage is about -20μA for the silicon diode, while for the germanium diode the reverse voltage is about -50μA. In this scenario, potential energy across the arrowhead terminal is negative, while on the other terminal potential energy is positive.

Zero-biased Diode

For the zero-biased diode, the voltage potential across the diode’s ends will be zero in zero-biased diode.

1.4 Diode test

In the forward biased connection, a normal diode will allow the current to flow through the circuit by closing it in one direction. In this scenario, the diode produces a small voltage drop in the circuit where it is connected. In the reverse-biased diode, this difference is too much. The voltage drop across the ends of the diode can be easily checked with the help of smart digital multimeters or voltage meters. The normal voltage drop across the forward-biased connections is about 0.6 volts to 0.9 volts. An ideal diode is one that has zero resistance for the current, but in a practical case, that is not possible. In the forward biased connection, a normal diode has about 1000 ohm to 10 million ohms resistance. In the reverse-biased diode, when the resistance is measured across the diode’s terminal with the help of a multimeter, the display of the multimeter shows “OL” (that shows a very high resistance). 
When the red probe of the multimeter is connected with the diode’s anode and the black probe is connected with the diode’s cathode, then the diode is forward biased. As the multimeter is connected with the forward-biased, the multimeter will produce a beep sound, indicating that the current is flowing through the diode. When the multimeter red test lead is connected with the diode’s negative terminal and the black test lead is connected with the diode’s arrowhead (positive) terminal, then the diode is reverse-biased. As the multimeter is connected with the reverse-biased, the multimeter will not produce a beep sound, indicating that the diode has very high resistance and the current is not able to flow through the diode.
Every diode has a specific current rating. When the current flows more through the diode than the specific rating, then the diode may fail and it will behave in two possible ways.
a). Current will be able to flow in forward as well as reverse direction
b). Or the current will not flow in any directions

1.5 Diode Applications 

Following are the important uses of the diode:
●Diodes as a rectifier
●Diodes in the clipping circuit
●Diodes in clamping circuits
●Diodes in logical gates
●Diodes in reverse current protection

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