Diodes Guide

A diode is a basic electronic component that allows electric current to flow in only one direction. Diodes act like a one-way valve for electricity: current can pass easily in the forward direction, but is blocked in the reverse direction.

How does a diode work?

A diode works because of a “p-n junction”. This is a place where two different types of semiconductor materials are joined together: p-type and n-type.

The junction is formed by joining the two types of semiconductor material: p-type (which has an abundance of “holes” or positive charge carriers) and n-type (which has extra electrons).

At the boundary where they meet, electrons from the n-side combine with holes from the p-side, creating a region with very few free charge carriers. This region is called the depletion zone, and it acts like a barrier that controls whether current can pass through the diode.

When the diode is connected in the correct direction, known as forward bias, the external voltage pushes charges toward the junction in a way that reduces the depletion zone. Once the applied voltage is strong enough to overcome this barrier, electrons can cross the junction easily, allowing current to flow through the diode. This is why a diode conducts in one direction—it essentially “opens the gate” only when the conditions are right.

When the voltage is reversed, called reverse bias, the opposite happens: the external voltage pulls charge carriers away from the junction, widening the depletion zone. This makes it very difficult for current to pass, so the diode effectively blocks it. In an ideal diode, no current would flow at all in this direction, but in real materials a tiny number of charge carriers still leak across, resulting in a very small leakage current.

What are diodes used for?

Diodes are used in a wide range of electronic systems because controlling the direction of current is fundamental in circuit design.

One of the most common uses is rectification, where diodes convert alternating current (AC) into direct current (DC). This is essential in power supplies for almost all electronic devices, from phone chargers to computers. By arranging diodes in specific configurations, AC power from the mains can be turned into usable DC voltage.

Diodes are also used for signal protection. In circuits, sudden voltage spikes (such as from motors or static discharge) can damage sensitive components. Protective diodes, often called flyback or clamp diodes, safely redirect excess voltage away from delicate parts.

Another important application is signal processing, where diodes are used to clip or clamp signals, shape waveforms, or detect radio signals. In communication systems, they help extract information from modulated signals, such as in AM radio receivers.

What types of diodes are there?

There are numerous types of diodes, each designed for specific functions and most hidden from view but essential to so many functions of day-to-day life:

Standard (rectifier) diodes

These diodes are the most basic and widely used type of diode, designed mainly to convert alternating current (AC) into direct current (DC). They allow current to flow in one direction only, which makes them essential in power supply circuits where electricity from wall outlets (which constantly changes direction) needs to be turned into a stable DC voltage for electronic devices.

Zener diodes

Zener diodes are a specifically designed to allow current to flow not only in the forward direction (like a standard diode) but also in the reverse direction, once a specific voltage threshold is reached. This special threshold is called the Zener breakdown voltage. Unlike regular diodes, which can be damaged by reverse breakdown, Zener diodes are carefully engineered to withstand the reverse breakdown.

LEDs (Light emitting diodes)

LEDs (Light Emitting Diodes) are a type of diode that produce light when an electric current flows through them in the forward direction. They’re one of the most commonly referred to types of diodes in modern life. Like all diodes, they are made from a p-n junction semiconductor, but they are specially designed so that when electrons recombine with “holes” at the junction, the energy released is emitted as photons—this is what creates light. The colour of the light depends on the materials used in the semiconductor and the energy band gap, which determines the wavelength of the emitted light.

Schottky diodes

Schottky diodes are a special type of diode that are designed for very fast switching and low voltage loss. Unlike standard diodes, Schottky diodes are formed using a junction between a metal and a semiconductor (usually n-type silicon). This is called a metal–semiconductor junction, and it gives Schottky diodes their unique performance characteristics. You might be interested to learn that. Schottky diodes are named after the German physicist Walter H. Schottky. He made important contributions to the understanding of semiconductor physics and metal–semiconductor junctions in the early 20th century.

Photodiodes

Photodiodes are a type of diode that are designed to detect light and convert it into electrical current. Like other diodes, they are made from a p-n junction, but they are engineered so that light can interact with the junction and generate charge carriers. When photons (light particles) strike the semiconductor material, they provide enough energy to create electron–hole pairs, which produce a measurable current.

Veractor (Varicap) diodes

Varactor diodes (also called varicap diodes) are a special type of diode designed to act like a voltage-controlled capacitor. Unlike standard diodes, varactor diodes are used to control capacitance electronically. They work because of what happens in the depletion region of a p-n junction. When a diode is reverse biased, no current flows, but the width of the depletion region changes depending on the applied voltage. In a varactor diode, this change is carefully engineered so that the junction behaves like a capacitor whose capacitance varies with voltage: higher reverse voltage widens the depletion region and reduces capacitance, while lower voltage narrows it and increases capacitance.

Avalanche diodes and TVS diodes

Avalanche diodes are designed to safely operate in a controlled form of reverse breakdown (similar to Zener diodes but based on a different physical mechanism). They are often used in voltage surge protection and also in some RF noise generation applications. Closely related are TVS (Transient Voltage Suppression) diodes, which are specifically built to protect circuits from sudden voltage spikes like electrostatic discharge or lightning-induced surges.

Tunnel diodes and PIN diodes

Tunnel diodes use a quantum mechanical effect called tunnelling to allow extremely fast switching. These are not widely used in everyday electronics anymore, but they are still important in high-frequency and specialised microwave applications. Similarly, PIN diodes (which have an additional intrinsic layer between p and n regions) are widely used in RF switches, attenuators, and photodetectors because they can handle high frequencies and power levels efficiently.

Lasers diodes and IR diodes

Laser diodes produce coherent light (a focused, single-wavelength beam) and are used in fibre-optic communications, barcode scanners, laser pointers, and Blu-ray/DVD drives. Another variant is the IR (infrared) diode, commonly used in remote controls and short-range communication systems.

Diodes summary

Diodes are fundamental electronic components that allow current to flow in only one direction, using a semiconductor junction to control electrical movement. Their importance comes from the fact that they enable safe, controlled, and efficient operation of almost all modern electronic devices, from phone chargers and computers to communication systems and advanced industrial equipment.

Ashlea Components stock and can supply a wide range of diodes. Explore our diodes range: