The term diode derives from a Greek word that can be translated as “narrow passage”. The concept is used in the field of electricity to name the valve that has a pair of electrodes and only allows current to pass in one direction.
To understand what a diode is, therefore, we must know what electrodes are. This is the name given to the end of an electrical conductor that is linked to a medium, from which it receives or to which it transmits a current.
Diodes are electronic parts that have two electrodes and that allow the advance of electric current in only one direction. Up to a certain potential difference, the diodes work as an open circuit that do not conduct electricity; On this difference, instead, they act as a closed circuit whose resistance is very low.
The first diodes were known as vacuum diodes, since they were glass tubes made up of two electrodes that were surrounded by a vacuum. These diodes were devised by the English engineer John Ambrose Fleming (1848-1945) at the beginning of the 20th century.
Over time, vacuum diodes fell into disuse and were replaced by semiconductor diodes. In this case, the valves have a semiconductor material that is linked to the electrodes. Types of semiconductor diodes include silicon diodes, crystal diodes, light- emitting diodes, avalanche diodes, and thermal diodes.
Light-emitting diodes, known by the English acronym LED, are characterized by the possibility of emitting light, producing a wavelength that varies from infrared to almost ultraviolet. Due to low power consumption, low heat emission, long lifespan and small size, light-emitting diodes are an increasingly popular lighting source. According to Abbreviationfinder, LED stands for Light Emitting Diode.
As mentioned in previous paragraphs, the diode conducts current in only one direction, and this represents its most characteristic feature. As with many other creations that were revolutionary in their time, it is not necessary to fully understand how it works from a physical point of view or how the diode is made to be able to use it, even in highly complex circuits.
The non-linear equation that can be seen in the second image shows us how to model the so-called iv curve of a diode, where i is the diode, Is is the reverse saturation current (in the case of silicon, it is usually 10 high at least 12 amps), q represents the charge on the electron, k is Boltzmann ‘s constant, and T is the temperature in kelvins.
One of the fundamental concepts in this context is the forward current, which occurs if a positive voltage is fixed by means of a silicon diode, locating us to the right of the iv curve. For a low value, such as +0.2 volts, there is almost no forward current, while when we reach +0.6 volts, a measurement is already possible. Past that value, the current increases rapidly, making the curve practically vertical.
This allows us to understand that the iv curve of the diode is not linear. The bias is forward when the voltage across its two terminals is positive, as in the example above.
To represent a diode, it is necessary to express the direction in which the current and the voltage flow (which must also have the + and – signs to indicate the orientation, the positive end being the one that receives the forward current). An orange curve should also be drawn to highlight the polarity of the voltage. All this can be seen in the second image.