Diodes

Diodes

Axial, Schottky and SOD

Conducts in one direction

Diodes

 

A diode is two-terminal electronic component that conducts current flow in only one direction and restricts current from the opposite direction with  a P-N Junction or an alternative junction.  Think of it as a “one-way street” for electric current. Shown below is classification of diodes by structure.

The PN junction of diode, is formed by joining two doped regions of semiconductor material, one p-type and one n-type. The type of doping determines whether the material has an excess of positive or negative charge carriers.

The different types of diodes in the image have different structures and properties, which makes them suitable for a variety of applications. For example, rectifier diodes are used to convert alternating current (AC) to direct current (DC), while Zener diodes are used to regulate voltage and some for signal modualtion isolation, stabalization and signal gating.

Schottky barrier diodes are another type of diode with a different structure, which uses a metal-semiconductor junction instead of a p-n junction. This gives them some unique properties, such as a lower forward voltage drop.

Diodes are sometimes classified not only as in the above figure, but also by usage. 

WHAT ARE DIODES USED FOR?

  • REVERSE CURRENT PROTECTION: Diodes allow current to flow in only one direction, protecting components from damage due to reverse current. For instance, they prevent a battery from being discharged back into the charging circuit.

  • SIMPLE VOLTAGE REGULATORS : By exploiting the voltage drop across the diode, which is relatively constant, diodes can be used in simple voltage regulator circuits to maintain a steady output voltage.

  • VOLTAGE STABILIZERS: Zener diodes, a special kind of diode, can be used as voltage stabilizers or references by maintaining a constant voltage over a wide range of current flows.

  • CONVERTING AC TO DC: Diodes are used in rectifier circuits to convert alternating current (AC) to direct current (DC). A full-wave rectifier, for example, uses multiple diodes to convert both halves of an AC waveform to pulsating DC

Each of these applications takes advantage of the diode’s fundamental property: allowing current to flow freely in one direction while offering high resistance in the other. This principle is key to many electronic circuits and devices

HOW DOES A DIODE WORK?

To fully understand how a diode works, basic concept of coventional flow theory should be understood. In coventional flow theory, current flows from the positive terminal of the battery to the negative terminal, as electron moves it leaves 'holes' behind. The holes are said to travel in the opposite direction from the electrons in the conductor.  

For a diode to block current in one flow and pass current in the opposite direction, joining a P type material with N-type material thus creating a PN junction at their boundary layer. The basic mechanism at the PN junction can be descrive as follows:

  1. Diffusion: The n-material has electrons as charge carriers and p-material has holes (places depleted of electrons) as charge carriers. Due to the concentration gradient, holes from the P-region and electrons from the N-region start to diffuse into each other's region.

  2. Formation of the Depletion Region: As the electrons and holes meet, they recombine and neutralizes each other. This leaves behind charged ions, creating a neutral region devoid of charge carriers called the depletion regio, prevents further electron flow.

  3. Built-in Potential: The recombination process creates a potential difference across the junction, called the built-in potential. This potential opposes further diffusion.

  4. Equilibrium: The diffusion and drift of charge carriers reach a dynamic equilibrium. The depletion region extends deeper into the N-region due to the higher mobility of holes in the P-region.

Key Concepts

Forward-biased Condition: When an external voltage is applied such that the P-region is connected to the positive terminal and the N-region to the negative terminal, overcoming the built-in potential, allowing charge carriers to move across the junction.

Reverse-biased Condition: When an external voltage is applied in the opposite direction, the built-in potential increases, widening the depletion region preventing charge carriers from moving across the junction. 

Forward Biased Diode
Reversed Biased Diode

Reverse Bias Leakage​: 

 

Breakdown Voltage: 

 

Diode Cheat Sheet
Diode Used For Special Characteristics Applications
Rectifier Diode, 
Fast Switching 
Rectifier
Converting AC to DC; Linear and switching  power supplies  Can be used in very high 
current capacities, improved efficiency and reduced loss, High Voltage Resistance

Power Supplies, Battery Chargers, HVAC Systems, Variable Frequency Drives (VFDs), Cathode Ray Tube (CRT) Displays

Sustain circuits in plasma display panels (PDPs), power factor correction (PFC) circuits, and radio signal detectors

Signal Diode HF rectification, detection     
Zener Diode Voltage reference, regulation     
Light-emitting 
Diode [LED]
     
Photodiode       
Optocoupler      
Schottky Diode      
Varactor Diode       
 Varistor      
 Current 
Regulator
     
 Step-recovery 
Diode
     
 Back Diode       
Laser Diode       
 Tunnel Diode      
 PIN Diode      

Applications of Diodes:

  • Rectification: Diodes are used to convert alternating current (AC) to direct current (DC) by allowing current flow in one direction.
  • Regulation: Diodes help regulate voltage levels in power supplies and voltage stabilizers.
  • Signal Modulation: Diodes play a role in signal modulation circuits.
  • Signal Isolation: They isolate signals from a supply, such as removing negative signals from AC current (signal demodulation).
  • Logic Gates: Millions of diodes are used in modern processors for digital logic.
  • Light-Emitting Diodes (LEDs): These are p-n junctions that emit light when a current flows through them.
  • Zener Diodes: Maintain a constant voltage despite fluctuations in voltage or current.
  • Varactor (Varicap) Diodes: Varying the bias voltage changes the diode’s capacitance, useful for signal transmission in radio and television industries