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Diode - Definition, Symbol, Construction, Types, Characteristics and Applications

A diode is a two-terminal electrical component that typically conducts current in one direction. On one end, it has a high resistance, whereas, on the other, it has a low resistance. Let us learn about diodes and diode symbols in-depth in this post.

Define diode

Diodes are used to safeguard circuits by limiting voltage and converting alternating current (AC) to direct current (DC). Semiconductors such as silicon and germanium are utilised to create the best diodes. Despite the fact that they both transfer electricity in the same direction, the manner in which they do so differs. There are several types of diodes, each with its own set of applications.

ALSO READ: Semiconductor definition

The Diode Symbol

The sign for a typical diode is seen above. We can see in the diagram above that there are two terminals called anode and cathode. The anode that reflects the typical current flow direction in the forward biassed situation is shown by the arrowhead. The cathode is at the opposite end.

Construction of Diodes

Diodes can be constructed of either silicon or germanium, the two semiconductor materials. When the anode voltage exceeds the cathode voltage, the diode is said to be forward-biased, and it conducts quickly with a minimal voltage drop. Similarly, when the cathode voltage is higher than the anode voltage, the diode is said to be reverse-biased. When a diode conducts, the arrow in the diode symbol reflects the direction of conventional current flow.

A diode is of the following types:

  • LED (Light Emitting Diode)
  • Diode
  • The avalanche
  • Zener
  • The Schottky
  • Photodiode
  • Diode with PN junction

Light Emitting Diode (LED): Light is created when an electric current between the electrodes travels through this diode. To put it another way, light is produced when a significant quantity of forwarding current flows through it. This light is not visible in many diodes because the frequency levels do not permit sight. LEDs come in a variety of colours. There are tricolour LEDs that can emit three different colours at the same time. The colour of light is determined by the energy gap of the semiconductor employed.

Diode Laser

It is a unique sort of diode since it emits coherent light. It is widely utilised in CD drives, DVD players, and laser printers. These are more expensive than LEDs but less expensive than other laser producers. The sole disadvantage of these diodes is their short lifetime.

The Avalanche Diode

This diode is reverse biassed and functions using the avalanche phenomenon. The breakdown of avalanche occurs when the voltage drop is continuous and independent of the current. They have great sensitivity and are hence utilised for photodetection.

Diode Zener

Because it can give a steady reference voltage, it is the most valuable form of diode. These are operated in reverse bias and fail when a specific voltage is applied. A steady voltage is created if the current going through the resistor is restricted. Zener diodes are commonly used to provide a reference voltage in the power supply.

Schottky Diode

Its forward voltage is lower than that of other silicon PN junction diodes. The decrease will be visible when there are a low current and voltage ranges between 0.15 and 0.4 volts at that point. In order to achieve that performance, they are built differently. In rectifier applications, Schottky diodes are widely utilised.


A photodiode can detect even small amounts of current flow caused by light. These are quite useful in detecting light. This is a reverse bias diode, which is found in solar cells and photometers. They're even utilised as power generators.

Diode P-N Junction

The P-N junction diode is sometimes referred to as a rectifier diode. These diodes are constructed of semiconductor material and are utilised in the rectification process. The P-N junction diode is made up of two layers of semiconductors. The semiconductor material is doped with P-type material on one layer and N-type material on the other. The P-N junction is formed by the combination of both P and N-type layers. As a result, the P-N junction diode was born. The P-N junction diode permits current to flow in one direction while blocking current flow in the other.

Diode Characteristics

The diode has the following characteristics:

  • Diode with forward bias
  • Diode with reverse bias
  • Diode with no bias

Diode with Forward Bias

When the diode is forward-biased and the current is conducting, there is a tiny voltage drop across it. The forward voltage for silicon diodes is 690mV, whereas the forward voltage for germanium diodes is 300mV. The potential energy across the p-type material is positive, while the potential energy across the n-type material is negative.

Diode with Reverse Bias

When the voltage from the battery is entirely removed, the diode is said to be reverse-biased. The reverse voltage for silicon diodes is -20A, whereas the reverse voltage for germanium diodes is -50A. The potential energy across the p-type material is negative, while the potential energy across the n-type material is positive.

Applications for Diodes

The diode has the following applications and uses:

  • As a rectifier, diodes are used.
  • The clipping circuit is made out of diodes.
  • Diodes are used in clamping circuits.
  • In logical gates, diodes are used.
  • Diodes that guard against reverse current
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