Diodes Overview
Diodes are amongst the most simple of electronic components, but their special characteristic of letting or restricting the flow of current through a circuit enable it to be used as an electronic switch within a circuit thus making them cost effective, efficient and versatile passive components that are featured within almost every design and circuit produced today. The word “diode” comes from ancient Greek “di” meaning twice and “hodos” meaning way. Diodes are also known as PN junction diodes or crystal diodes. On a diode, the silver stripe marking indicates the cathode (negative) end.

What is a Diode?
A diode is a passive electronic semiconductor component that allows current in a circuit to flow in one direction (the forward direction) but not the other – basically like a one-way valve – the diode effectively stops current from traveling in the other direction. The amount of current that the diode lets through the circuit is determined by the diode itself, which gives it its particular benefit and characteristic as an passive component – this is in turn determined by the voltage being passed between the diode. The diode has two terminals – the anode is the positive terminal and the cathode is the negative terminal. Diodes only allows current to pass when the anode is made “more positive” than the cathode and are used in many appliances like switches, voltage regulators and rectifiers. If polarity is reversed (reverse biased) current flow is blocked within the rated limits of the diode.  Generally diodes are made from silicon or germanium

How do Diodes work?
Diodes comprise of two layers of semiconductor materials which together form a PN junction. In the N-type layer, phosphorus or arsenic is added, in parts per billion, to the silicon in small quantities, which create electrons in a negative charge. In the P-type layer, boron or gallium is added to the pure silicon forming conductive holes in the electrons, causing a positive charge to be created.

The P-type material has a surplus of positive charge carriers (holes) and the N type, a surplus of electrons. Between these layers, where the P-type and N-type materials meet, holes and electrons combine, with excess electrons combining with excess holes to cancel each other out, so a thin layer is created that has neither positive nor negative charge carriers present. This is called the depletion layer. There are no charge carriers in this depletion layer and no current can flow across it.  But when a voltage is applied across the junction however, so that the P-type anode is made positive and the N-type cathode negative, the positive holes are attracted across the depletion layer towards the negative cathode, also the negative electrons are attracted towards the positive anode and current flows.  When current is flowing through a diode, the voltage on the positive leg is higher than on the negative leg, this is called the diode’s forward voltage drop. The severity of the voltage drop is a function of  the semiconductor material that the diode is made from. When the voltage across the diode is positive, a lot of current can flow once the voltage becomes large enough. When the voltage across the diode is negative, virtually no current flows.  When current is flowing through a diode, the voltage on the positive leg is higher than on the negative leg, this is called the diode’s forward voltage drop. The severity of the voltage drop is a function of  the semiconductor material that the diode is made from. When the voltage across the diode is positive, a lot of current can flow once the voltage becomes large enough. When the voltage across the diode is negative, virtually no current flows. When negative side of an external voltage is connected to diode cathode, and positive to anode, the diode is said to be forward biased with the electrons and electron holes forced towards the central junction between the layers. If the potential difference is more than the junction threshold volatge (0.6v silicon, 0.2 germanium, 0.4 Schottky) the charges pass through the junction – thus allowing current to flow and the dynamic resistence of the diode to reduce to almost zero as the circuit current rises. In reversed biased mode, electrons and electron holes (charges) are attracted away from the central junction, therefore blocking current flow. That being the case, some current does leak through (leakage) whilst the potential rises until it reaches breakdown voltage at which point the resistence is almost zero. The energy from this leakage is dissipated as heat.

Use of Diodes:
Rectifiers –  converting alternating current (AC) to direct current (DC)
Suppressors – stop or prevent voltage spikes from relay coils, motors or other devices
Protection – to protect components from reversed voltage
Voltage selection – sensitivity to relative voltage between terminals allows it to select the voltage
Voltage clamping / DC Restoring – positive or the negative peak excursions of a signal are fixed to a defined value by shifting its DC value
Logic gates –  Performing a logical operation on an one or more inputs such as AND, OR, XOR, NOT, NAND, NOR, and XNOR to produce a single logical output
DC Voltage Regulator – maintains a constant level of DC voltage
Noise Reduction – reducing random fluctuations within an electrical signal
AC Voltage Control – change the RMS value of the alternating voltage applied to a load circuit with tyristors between the load and a constant voltage ac source.
Signal Clipping / diode limiters – wave shaping circuit that takes an input waveform and clips or cuts off its top half, bottom half or both halves together to produce an output waveform that resembles a flattened version of the input.
Voltage sensing – Zener diodes can sense change in voltage and switch output accordingly

Diode Attributes:
Maximum sustained forward current: If, Io, Iomax
Forward voltage: Vf
Peak inversed DC Voltage (breakdown voltage, maximum blocking voltage) Piv, Vdc, Vbr
Maximium reverse current (leakage): Ir
Zener voltage: Vz
Zener impedence / dynamic resistence: Zz
Max Zener current: Iz Izm
Max or total power dissipation: Pd Ptot

Types of Diode:
Signal / Switching / High Speed – small in size, fast response times, can’t take high currents
Rectifier – larger than signal in size, can handle higher currents, not good for fast switching, have axial leads, may include a heat sink or be able to attach to a heat sink
Zener – regulates voltage, lower breakdown voltage than signal & rectifier diodes; reverse biased
Varactor/Varicap – reverse biased below its breakdown voltage, controls high frequency oscillators using variable capacitance controlled by reverse voltage; low maximum capacitance limits use to RF applications
Schottky – low junction capacitance, fast switching, lower forward voltage drop; made with semiconductor to metal  junction, more expensive than silicon
Tunnel – extremely fast diode that uses negative conductance: current decreases with increased forward voltage. Also known as Esaki diode after Japanese scientist Leo Esaki. useful in oscialltors and as a microwave amplifier as they perform in the microwave radio frequency. Current flow is determined by quantum mechanical particle tunneling
Backward  or back diode – similar to a Zener or tunnel diodes having better conduction for small reverse biases than for forward bias voltages.
Gunn or transferred electron device – uses only N-type semiconductor (so it’s not really a diode!), unlike normal diodes its I/V behaviour is symmetric, used for sources of microwave power. Allows current in one direction at which its resistance is very low during forward bias. In the other direction, it doesn’t allow the flow of current – as it offers a very-high resistance during reverse bias.
PIN – a diode which includes an intrinsic material layer which is doping free, can be made both on GaAs or silicon, suitable for attenuators, fast switches, photodetectors, and high voltage power electronics applications
Laser diode – electrically pumped lasers where the gain is generated by an electrical current flowing through a p–n junction or  a p–i–n structure
BARITT diode – Barrier Injection Transit Time, used mainly in microwave signal generation applications and products
Trapatt diode – Trapped Plasma Avalanche Triggered Transit, high efficiency microwave generator capable of operating from several hundred megahertz to several gigahertz
Photosensitve/Photodiode – adjusts current according to amount of light it senses (basically a sensor)
LED –  light emitting diode – highly effiencty light source; LEDs are simply diodes that are designed to give off light. When a diode is forward-biased so that electrons and holes are moving back and forth across the junction, they’re constantly combining and wiping one another out. After an electron moves from the n-type into the p-type silicon, it will combine with a hole and disappear, making an atom complete and more stable which then gives off a little burst of energy in the form of a photon of light
Transient Voltage Suppressor (TVS) – protects sensitive equipment from voltage spikes, diverting the energy to ground, up to 30000 volts or from electrostatic discharge (ESD),  fast response time, lower capacitance and low leakage current
Diode Array/ Bridge Rectifier – two or more diodes in a single DIP or IC chip
Step recovery diode – a junction diode that can produce short pulses for use as a charge controlled switch.

Diode Uses:
Battery Chargers
Broadcasting Stations
Communication Stations
Conventional Generator Market
Data Centers
Direct Broadcast By Satellite
Direct Or Fiber Coupled Applications
Gas Cogeneration
Home Electronics Market
Industrial Machinery Market
Information/Communications Market
Led Lighting
Machine Vision
Materials Processing
Measuring Equipment
Medical Equipment
Mobile / Portable
Mobile Base Stations
Mobility Market
Motor Control
Motor Drives
Power Management
Raman Spectroscopy
Solid State Laser Pump Sources
Traction Markets
Tv Displays

Diode Manufacturers in India List:
Induction Furnace Diode
Kura Electronics And Electricals
Salicon Nano Technology Private Limited
Power Engineers And Consultants
Kevin Electrochem
Altek Systems
Cosmic Devices
Shruti Mechatronics
Orbit Electronics
Sheetal Corporation
Elshaddai Engineering Equipments
Sheth Electronics
Insel Rectifier (India) Pvt. Ltd.
Continental Device India Limited
Naina Semiconductor Ltd
Arihant Enterprises
Orbit Electronics
Siricom Technology
Nilesh Sales Agencies
Shivam Metals
Kms Technologies
Leeds Electronic Industry Inc.
Shiv Shakti Enterprises
Contec Electronics
Power Key
Shindengen America, Inc.
Master Instrument Corporation
Sumeet Electronics


Diode Manufacturers List:
American Power Devices
Analog Devices Inc.
Avago Technologies
Bourns Inc.
Cavet Technologies
Central Semiconductor
Comchip Technology
Cree, Inc.
Diode Led
Diodes Incorporated
Diogen Lighting
Electronics Industry Public Company Limited
Fairchild Semiconductor
Fairchild/Minco Technology Labs Llc
Frankfurt Laser Company
Genesic Semiconductor
Inphenix Corporation
International Rectifier
Koa Speer
Lemnis Lighting
Lg Innotek
Maxim Integrated
Micro Commercial Components
M-Pulse Microwave
Nic Components
Nte Electronics
Nxp Semiconductors
On Semiconductor
Opto Diode Corporation
Optoelectronics Company
Osram Opto Semiconductors
Panasonic Electronic Components
Philips Lumileds
Power Integrations
Raychem / Te Connectivity
Renesas Electronics America
Rohm Semiconductor
Samsung Led
Seoul Semiconductor
Sep Electronic Corp
Solid State
Sprague Goodman
Taiwan Semiconductor
Te Connectivity
Texas Instruments
Topdiode Manufacturing Company
Tt Electronics
Us-Lasers, Inc
Vishay Semiconductor Diodes Division
Wurth Electronics

This is part of the EEIND.in Wikielectronics, a Glossary of Terms and Components used in Electronics Systems, Design and Manufacture. We welcome your comments, thoughts and additions to this article – or indeed if you have a component or area of electronics design that you would like to submit an article into our Wiki, please email this to the site editor: editor1@eeind.in and we’ll take a look!


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