Hello Dejan Nedelkovski here from
HowToMechatronics.com. In this tutorial we
will learn what capacitor is, how it
works and take a look at some basic
application examples. There is almost no
circuit which doesn't have a capacitor
on it and along with resistors and
inductors there the basic passive
components that we used in electronics.
A capacitor is a device capable of storing
energy in a form of electric charge.
Compared to a same sized battery a
capacitor can store much smaller amount
of energy, around ten thousand times
smaller but useful enough for so many
circuit design. A capacitor is
constructed out of two metal plates
separated by an insulating material
called dielectric. The plates are
conductive and they are usually made of
aluminum or other metals, while the
dielectric can be made of any kind of
insulating material such as paper, glass,
ceramic or anything that obstructs the
flow of the current. The capacitance of a
capacitor measured in Farads,
is directly proportional to the surface
area of the two plates, as well as the
permittivity of the dielectric. While the
smaller the distance between the plates
the greater the capacitance. That being
said now let's take a look how a
capacitor works. First we can note that a
metal typically has an equal amount of
positively and negatively charged
particles which means it's electrically
neutral. If we connect a power source or
a battery to the metal plates of the
capacitors a current will try to flow or
the electrons from the plate connected
to the positive lead of the battery
will start moving to the plate connected
to the negative lead of the battery.
However, because of the dielectric
between the plates the electrons won't
be able to pass through the capacitor so
they will start accumulating on the
plate. After a certain number of
electrons accumulated on the plate
the battery will have insufficient energy
to push any new electronics 
to enter the plate because of
the repulsion of those electrons which
are already there. At this point the
capacitor is actually fully charged. The
first plate has developed a net negative
charge and the second plate has
developed an equal net positive charge
creating an electric field with an
attractive force between them which
holds the charge of the capacitor.
Let's take a look how the dielectric can
increase the capacitance of a capacitor.
A dielectric contains molecules that are
polar which means that they can change
their orientation based on the charges
of the two plates. So the molecules align
themselves with the electric field in
such a way enabling more electrons to be
attracted to the negative plate while
repelling more electrons out of the
positive plate. So once the capacitor is
fully charged if we remove the battery
it will hold the electric charge for a
long time acting as energy storage.
Now if we shorten the two ends of the
capacitor through a load a current
will start flowing through the load the
accumulated electrons from the first
plate will start moving to the second
plate until both place become back again
electrically neutral. So that's the
basic working principle of a capacitor
and now let's take a look at some
application examples. Decoupling
capacitors or bypass capacitors are
typical example. Decoupling capacitors
are often used along with integrated
circuits and they are placed between the
power source and the ground of the IC.
Their job is to filter any noise in the
power supply like voltage ripples which
occur when the power supply for a very
short period of time drops its voltage
or when a portion of a circle is switch
causing fluctuations in the power supply.
At that moment when the voltage drop
occurs the capacitor will temporarily
act as a power supply bypassing the main
power supply. Another typical examples
are capacitors used in DC adapters.
For converting the AC voltage into a DC
voltage a diode rectifier is usually
used, but
without the help of capacitors it won't
be able to do the job. The output of a
rectifier is a waveform so while the
output of the rectifier rises the
capacitor charges and while the output
of the rectifier declines the capacitor
discharges and in that way smooth the DC
output. Signal filtering is another
application example of capacitors.
Because of their specific response time
they are able to block low frequency
signals while allowing higher frequency
to pass through. This is used in radio
receivers for tuning out undesired
frequencies and in crossover circuits
inside speakers for separating the low
frequencies for the sub-woofer and the
higher frequencies for the twitter.
Another rather obvious use of capacitors
is for energy storage and supply.
Although they can store considerably
lower energy compared to the same sized
battery their lifespan is much better
and they are capable of delivering
energy much faster which makes them more
suitable for applications where high
burst of power is needed. So that would
be all for this tutorial but you can
always find more details and tutorials
on my website HowToMechatronics.com.
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