How Capacitor works?
Animation and Analogy
The simplest capacitors
are big plates of metal close to each other but not touching. When connected to
a potential difference (e.g. a battery), the battery tries to push electrons
through the wire away from its negative terminal. Although there isn't a complete
circuit, you can imagine that you can shove a few extra electrons onto a big
sheet of metal . Let's face it, given the choice between being stuck at a
negative terminal or going to a neutral metal plate, electrons will get up and
move! So you get a flow of electrons to the plate i.e. you get a current
without a complete circuit, but only for a short period of time.
(Image: Capacitor works)
At the start the
capacitor is fully discharged.
When the switch is
closed, the capacitor is charged up from the energy stored in the battery until
the capacitor has the
same voltage as the battery. At first it charges up rapidly and then gradually
slows.
Open switch. The capacitor
remains fully charged.
Pushing the RESET button
short circuits the capacitor and the energy stored in the capacitor is now
discharged, slowly
at first. With small capacitors the energy discharge is very fast, almost
immediate.
With large capacitors,
this can take a long time.
This is why capacitors
are used in timing circuits.
Capacitor Analogy
Think of water flowing
through a pipe. If we imagine a capacitor as being a storage tank with an inlet
and an outlet
pipe, it is possible to show approximately how an electronic capacitor works.
First, let's consider
the case of a "coupling capacitor" where the capacitor is used to
connect
a signal from one part
of a circuit to another but without allowing any direct current to flow.
(Image: Capacitor passes AC
in coupling circuits)
If the current flow is
alternating between zero and a maximum, our "storage tank" capacitor
will
allow the current waves
to pass through.
(Image: Capacitor blocks DC
in coupling circuits)
However, if there is a
steady current, only the initial short burst will flow until
the "floating
ball valve" closes and stops further flow.
So a coupling capacitor
allows "alternating current" to pass through because the ball valve
doesn't
get a chance to close as
the waves go up and down. However, a steady current quickly fills the tank
so that all flow stops.
Now, lets think about
the De-coupling Capacitor
(Image: Capacitor bypassing
the AC in de-coupling circuits)
Where a capacitor is
used to decouple a circuit, the effect is to "smooth out ripples".
Any ripples, waves
or pulses of current are passed to ground while d.c. flows smoothly.