LED Series Resistance
• The series resistor value RS
is calculated by simply using Ohm´s Law,
by knowing the required forward current IF of the LED, the supply
voltage VS
across the combination and the expected forward voltage
drop of the LED, VF
at the required current level, the current limiting resistor is calculated as:
Light Emitting Diode The “Light Emitting Diode” or LED as it is more commonly called, is basically just a specialised type of diode as they have very similar electrical characteristics to a PN junction diode. This means that an LED will pass current in its forward direction but block the flow of current in the reverse direction. • Light emitting diodes are made from a very thin layer of fairly heavily doped semiconductor material and depending on the semiconductor material used and the amount of doping, when forward biased an LED will emit a coloured light at a particular spectral wavelength. • When the diode is forward biased, electrons from the semiconductors conduction band recombine with holes from the valence band releasing sufficient energy to produce photons which emit a monochromatic (single colour) of light. Because of this thin layer a reasonable number of these photons can leave the junction and radiate away producing a coloured light output. • Also, nearly al...
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