How a Capacitor Works - Capacitor Physics and Applications

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Language: en

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