now the next type of cap is ceramic now
that this so tiny I'm not even going to
show you but the move to ceramics is
almost completely the advances in
ceramic technology over the years is
just amazing this keeps getting better
they use they're probably the most
popular capacitor by far on the planet
and they use for all sorts of things now
when talking about ceramic capacitors
there are two basic classes defined by
the EIA class 1 and class 2 class 1
ceramic capacitors are the NPO and CAG
types they do come in other types but
they're the two main ones and the
advantage of class 1 ceramic caps is
that they do not change with temperature
they're very very stable but they only
come in low values that's a major
disadvantage now the second type is
class 2 tire capacitors and there's more
varieties that you can poke a damn
sticker but some of the more common ones
you'll hear terms like X 7 or X 5 are y
5v z 5u and this is a code the first
character means it's the minimum
temperature in this case X is better
than Z the second character defines the
maximum temperature of the capacitor and
in this case a high numbers better 7s
better than 5 and the third digit is the
temperature coefficient how much change
in capacitance you get with that
temperature range and in this case R is
better than you are might be plus minus
15% but once you get down into V and you
the absolutely horrible minus 82 percent
minus 56 percent these things absolutely
shocking atrocious now generally ceramic
capacitors are known as multi-layer
capacitors due to their construction of
multi layers between the two end caps
and that's their more common term now
multi-layer chip capacitors ceramic
capacitors are used by their zillions
you can't count these things and they're
used for general purpose stuff like our
bypassing and filtering and things like
that because there's a whole grade and
whole variety of ceramic capacitors for
all these different purposes I'm a very
stable some are just absolutely
atrocious that you only use for you know
rough decoupling applications and things
like that
so it's very important to choose the
right type of ceramic capacity Cantor's
WAC any ceramic capacitor in there it
probably won't work now one weird thing
about class two ceramic capacitors
because of their because their ceramic
and the multi-layer construction they
are absent they are actually what's
called our microphonic due to the
piezoelectric effect any sound or
vibration in either directly into the
capital via the board can actually flex
it and it can generate a voltage just
like a microphone these things will
actually pick up and translate sound and
this phenomenon also works backwards so
if you drive this with a voltage add
some audio frequency or something like
that you can actually these things will
actually flex and they'll actually
generate sound and the PCB can be used
the PCB substrate can actually act as an
amplifier and these things can you can
actually hear these things it's it's
it's not fairly common but if you're
working on precision audio stuff this
can actually be quite important Oh micro
phonics watch out for it now this are
same microphonic phenomenon can also
happen in other caps like film caps as
well but not as much and it can also
happen in cables and other thinkers
because to remember cables or capacitors
to and they can have our micro phonics
and drive our electric effects as well
go and google that one a ceramic
capacitors are can fail short circuit
but they usually the main problem with
them is that they are very very brittle
very very fragile you can damage them
solder in on the board with excess
temperature handling and flex on the PCB
as well if you mount them in one
direction and you flex the board like
this you can actually crack they can get
micro cracks in them and that can be a
real problem for long term reliability
and things like that so just be very
very careful with how you mount and
handle multi-layer ceramic capacitors
right so that's the end of the
capacitors but I think we've got a
couple of seconds to explain an
important characteristic of capacitors
which is pretty neat and a lot of people
don't understand
now it's the impedance versus frequency
characteristic of a capacitor it's going
to look something like this
now the model of a capacitor is the ESR
in series with the capacitive reactance
which changes with frequency and the
inductive reactance as well which also
changes with frequency and this is the
total impedance so the graph is the
impedance versus the frequency and looks
like this now at low frequencies the the
actual capacitive reactance is going to
dominate and then at higher frequencies
the inductive reactance is going to take
over and that's going to dominate the
total impedance of the capacitor and
there's going to be a resonant point
here where these two things are equal
and you know and that's the best place
to operate the capacitor at in terms of
impedance now the important thing about
this is that it comes into play you've
probably seen multiple capacitors in
parallel all these different values
across a chip for decoupling and what
the reason they do this is because each
capacitor will have a different
characteristic like this each value so
your total will look something like that
and you get a much lower capacitance
over the entire frequency range and
that's why you put them in parallel it's
not as silly as it sounds it's actually
quite a valid technique that can gain
you quite a considerable performance in
terms of decoupling and EMI and things
like that so there you go ha that's it
there you go that's the end of
capacitors how do you choose a capacitor
I don't know don't ask me it's too
complicated Oh