Definition of DIODE
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 the passage of the current in a single direction .
To
understand what a diode is, therefore, we must know what the electrodes
are.
This is what is called the end of an electrical conductorthat is
linked to a medium, from which it receives or to which it transmits a current . The diodes
are electronic pieces
that have two electrodes and that
allow the advance of the electric current in only one direction. Up to a
certain potential difference, the diodes function as an open circuit that does
not conduct electricity ; on the difference, however, act as a
closed circuit whose resistance is very low.
The first
diodes were known as vacuum diodes , since they were glass tubes
formed by two electrodes that were surrounded by vacuum . These
diodes were designed by the English engineer John Ambrose Fleming (1848-1945)
at the beginning of the 20th century. Over time,
the vacuum diodes became obsolete and were replaced by
semiconductor
diodes . In this case, the valves have a semiconductormaterial that
is linked to the electrodes.
The types of semiconductor diodes shown silicon
diodes , the crystal diodes , the light - emitting
diodes , the 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 energy consumption ,
low heat emission, long service life and small size, light-emitting diodes are
an increasingly popular source of illumination.
As mentioned
in previous paragraphs, the diode conducts current in only one direction , and this represents its most characteristic feature. As it happens with
many other creations that were revolutionary in their time, it is not necessary
to understand thoroughly how it works from a physical point of view or how the
diode is manufactured to be able to use it, even in very complex circuits.
The nonlinear 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 at least 12
amps), qrepresents the charge of the electron, k is the Boltzmann
constant and T , the temperature in Kelvin. One of
the
fundamental concepts in this context is the current of advance ,
which occurs if by means of a silicon diode a positive voltage is
set, placing us to the right of the curveiv.
For a low value, such
as +0.2 volts, there is almost no advance current, while when we reach +0.6
volts it is already possible to make a measurement. After 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 polarization is
direct when the voltage between its two terminals is positive, as in
the previous example.
To represent
a diode it is necessary to express the sense in which the current and the
voltage advance (which must also present the + and - signs to
indicate the orientation, the positive end being the one receiving the forward
current). You should also draw an orange curve to highlight the polarity of
the voltage. All this can be seen in the second image.
