LED Diode Tutorial – Construction, Characteristic

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Light-emitting diode (LED, LED diode) – a type of semiconductor diode, also one of the optoelectronic components. The simplest LEDs are implemented as ordinary p-n semiconductor junctions. After LED diode polarity is forward-biased with enough voltage it starts emiting electromagnetic radiation in the visible and infrared light.

led diodeLED diode symbol

LED diode construction:

Color and wavelength of radiation emitted by LEDs are closely connected with the semiconductor material from which it was made.  Usually they are manufactured from compounds (bicomponents and multicomponents) of elements from III and V group of the Mendeleev’s Periodic Table (for example, GaAs – gallium arsenide, GaP – gallium phosphide, GaAsP – arseno-phosphide gallium with right-doping). Elemental composition of the diode is assorted in a way that semiconductor structure obtained in the process will allow the emission of light in the desired spectral range. “p-n junctions” of LEDs with GaAs are mostly produced with a diffusion technique. It ensures a high quantum efficiency. Group of interconnected diodes are used in various types of displays for example in seven-segment displays.

led diode

The division of LEDs based on the color of light radiation:

Color Wavelenght λ [nm]
Ultraviolet (UV) < 380
Violet 380 – 435
Blue 435 – 500
Blue-Green 500 – 520
Green 520 -565
Yellow 565 – 590
Orange 590 – 625
Red 625 – 700
Infrared (IR) > 700

Smooth change of wavelength is accompanied by analogous change in colour. In the table above we’ve put ranges of  wavelength values in length-order to improve envision of the relation between wavelength and diode colour.

 

led diode characteristic

The group of current-voltage characteristics of LED

Working principle of LEDs:

The principle of light-emitting diode operation is based on the electroluminescence phenomenon (producing light under the influence of the electric field). Electroluminescence occurs as a result of recombination (annihilation) pair of carriers (electrons and hole) in the area of the “p-n junction”. While electrons flow from higher to a lower energy-level, power dissipation occurs as a heat (non-radiative recombination – at semiconductors with n-oblique energy gap) or light (radiative recombination – semiconductors with a simple energy gap). During this flow, electron energy is converted into a quantum of electromagnetic radiation.

Advantages of Light-Emitting Diodes:

  • ability to choose light colors,
  • low working voltage (single LEDs need from 2 to 4V),
  • low power consumption,
  • small sized component (compared to a standard bulb even very small),
  • high efficient,
  • low energy losses,
  • durable.

Examples of LEDs varieties:

  • RGB LED (Red Green Blue LED) – has three colors in “one box”, which allows to generate any color,
  • IR (Infrared) – it emits infrared radiation that is used for example in data transmission, also in older models of mobile phones (some of you may not remember this!),
  • HB LED (High Brightness LED) – diodes with high brightness. They are used in automotive, traffic lights, streetlights or in frontal bicycle lights.

 

 

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I'm Michael. Me and my friend John are students of electronics. We are creating this site to help students and any interested people understand electronics.

3 thoughts on “LED Diode Tutorial – Construction, Characteristic

  1. Vf is quite inaccurate for modern LEDs
    e.g. Blue Vf = 3V at 20mA or 2.9 @0.35A for high power ( same for white.)
    ESR ~= 16 Ohms for 65mW and 0.5 to 1 Ohm for 1 Watt diodes.

    All diodes have a threshold voltage and a rated Vf at some rated current which includes the ESR of the bulk resistance. The ESR is inversely proportional to the rated power of any diode including LEDs and the product term of ESR at rated current * Watts at some temperature like 25’C or 85’C is equal from 1 to 2 Watt-Ohms.

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