What is a Diode?

Simply put, a diode is a semiconductor device that essentially acts as a one-way switch for current. It allows current to flow easily in one direction but severely restricts current from flowing in the opposite direction. That said, there are a variety of different types of diodes with just as many functions and characteristics. Below are the most common diodes and their characteristics.

PN Junction Diode

A PN junction diode is a two-terminal electronic component that allows the flow of electric current only in one direction. In the forward biased condition, the diode allows the flow of the electric current but in the reverse biased condition, it blocks the flow of electric current.

PN junction diodes are made with semiconductors. N-type semiconductors are the majority carriers for free electrons and the P-type semiconductors where the majority carriers are holes, when they are joined to each other and make a PN junction then a diode is formed called PN junction diode. It is used as a rectifier, and also in the low current application, power applications, etc.

Shockley Diode

A Shockley diode is a four-layer semiconductor diode known as PNPN diode. The Shockley diode named after its inventor William Shockley. This type of diode is made with a set of interconnected bipolar transistors(one PNP and other NPN).

The last NP part of the PNP transistor is connected with the NP part of the NPN transistor. The Shockley diode is used as a trigger switch for silicon control rectifier, relaxation oscillator (sawtooth oscillator) and also it is used as an audio amplifier.

Tunnel Diode

A Tunnel diode is a heavily doped PN junction diode that has negative resistance due to tunneling. For this negative resistance the current decreases with increasing the voltage across the diode. The tunneling diode was invented by Leo Esaki when he working in quantum mechanics about electron tunneling effect.

The diode is used as a very fast switching device in computers and used as a logic storage memory device. and also it is used in high-frequency oscillators, amplifiers, and FM receiver.

Varactor Diode

Varactor is a type of PN junction diode that has capacitance which varies with varying the reverse-biased voltage. It operates only in reverse-biased voltage and acts as a variable capacitor.

The varactor diode is also known as varicap diode, tuning diode, and variable capacitance diode. The varactor diode is used in frequency multiplier and also it is used in parametric amplifier and voltage-controlled oscillators.

Avalanche Diode

Avalanche diode is a special type of semiconductor diode which operates in the avalanche breakdown region at a specified reverse-biased voltage. 

Avalanche diodes are used to protect the electrical system from excess voltage. so it is used as a relief valve that controls the pressure in the system. And also it is used as a white noise generator.

Light Emitting Diode

A Light Emitting Diode (LED) is an electronic component that can emit light when the electric current is passed through it. LEDs are made with semiconductors. When the electrons in the semiconductor recombine with holes then it released energy in the form of photons.

The color of the light is determined by the energy required for electrons to cross the energy bandgap of the semiconductors. Early LEDs produced only red light, but modern LEDs are made like that they can produce different colors such as yellow, green, blue. 


A photodiode is a type of semiconductor device which converts light energy to electrical current. The photodiode absorbed photons from sunlight and converts them to an electrical current. When the diode is in the dark no current will flow, but in light, the current willflow from the cathode to the anode.

A photodiode allows current to flow only in one direction that means it produced DC current only. The photodiode contains an optical filter that allows light to reach the sensitive part of the device and may have large or small surface areas. In a solar cell, a large area of photodiodes are used to produce electricity.

Common Uses for Diodes


The most common application, by far, is the use of diodes for the rectification of AC power to DC power. Using diodes, different types of rectifier circuits can be created, the most basic of which are half-wave, full-wave center-tapped, and full-bridge rectifiers. These are extremely important in electronics power supplies. For example, a laptop’s charger, where an AC current, which comes from the mains power supply, must be converted to a DC current which can then be stored.

Seven Segment Display

A seven-segment display is an electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix displays. Seven-segment displays are widely used in digital clocks, electronic meters, basic calculators, and other electronic devices that display numerical information.

Seven-segment displays can have a shared anode or cathode which means if they share a positive or negative terminal. Because it is eight combined LED's, polarity matters.

Over-voltage protection

Sensitive electronic devices need to be protected from surges in voltage, and the diode is perfect for this. When used as voltage protection devices, diodes are nonconducting, however, they immediately short any high-voltage spike by sending it to the ground where it cannot harm sensitive integrated circuits. For this use, specialized diodes known as “transient voltage suppressors” are designed. These can handle large power spikes over short time periods which would normally damage sensitive components.