Diodes
A diode is an electronic device or component composed of a silicon
or Germanic semiconductor material in a crystalline film whose opposite faces
are doped by different
gases during their formation (electrons and holes).
There are two types of diodes, the Rectifier and the Zener, where
both have polarity in their application on the board so that they do their
functions.
Rectifier Diode
Rectifier diode is a unidirectional electronic component, that is,
it conducts electrical current in only one direction. The main function is to
rectify the signal. It is the simplest type of semiconductor electronic
component, used as an electrical current rectifier in transformers and others.
We have two situations where we can polarize the diode DIRECT POLARIZATION
and REVERSE
How to Test a Diode?
Internally the diode has a barrier (depletion zone) that separates the
two elements, this barrier causes a voltage drop when the diode is directly
biased (as the image above), this voltage drop can vary from diode to diode,
and also the material that is made (silicon or germanium). Generally speaking,
when we go to test the component, the ideal measure is that the value is
between 0.2v to 0.8v (using the multimeter in the semiconductor scale).
Test: Place the multimeter on the semiconductor scale then place the red
tip of the multimeter on the positive terminal of the diode, and the black tip
on the negative terminal.
Note: that the value on the multimeter will be from 0.2v to 0.8v.
If a different value appears, the component or if no value appears, the
component is defective.
Note: Always the side that has the range will indicate the negative
terminal (Cathode).
Zener Diode
Zener diodes have unique characteristics that make them suitable
for maintaining a fixed voltage in a circuit. We know that the voltages found
in household outlets tend to vary. On the other hand, electronic devices need
constant voltages to work properly. To keep the voltage constant in electronic
circuits, there are some devices, the most common being the Zeners diodes.
Together with other components they can receive voltages that vary and
transform them into constant voltages.
Operation
When directly polarized, a Zener diode conducts like a rectifier
diode, that is, from approximately 0.6V of voltage between its terminals, a
current starts to circulate. In this situation the voltage stabilizes at
approximately 0.7V. The big difference between rectifier diodes and Zener
diodes is in the negative bias region. Conventional diodes withstand the
reverse voltage up to a certain limit. Remember that when reverse-biased, a
diode does not conduct. However, when it reaches the limit of the reverse
voltage that the diode supports, it conducts very intensely and soon ends up
burning when it reaches the avalanche region.
SMD Diodes
They follow the same logic as the SMD resistors, where, as the electronic
equipment got smaller, the internal components too and consequently the diodes
followed the same line getting small and to save space were soldered directly
to the surface of the board. But the test and values are the same as PTH Diodes
(conventional).