/ News & Press / Video / EEVblog #33 2of2 - Capacitor Tutorial (Ceramics and impedance)

EEVblog #33 2of2 - Capacitor Tutorial (Ceramics and impedance)

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00:00:09.810
now the next type of cap is ceramic now
00:00:13.410 00:00:13.420 that this so tiny I'm not even going to
00:00:15.270 00:00:15.280 show you but the move to ceramics is
00:00:17.580 00:00:17.590 almost completely the advances in
00:00:19.890 00:00:19.900 ceramic technology over the years is
00:00:21.660 00:00:21.670 just amazing this keeps getting better
00:00:23.640 00:00:23.650 they use they're probably the most
00:00:25.439 00:00:25.449 popular capacitor by far on the planet
00:00:28.679 00:00:28.689 and they use for all sorts of things now
00:00:31.380 00:00:31.390 when talking about ceramic capacitors
00:00:33.120 00:00:33.130 there are two basic classes defined by
00:00:35.580 00:00:35.590 the EIA class 1 and class 2 class 1
00:00:38.400 00:00:38.410 ceramic capacitors are the NPO and CAG
00:00:41.279 00:00:41.289 types they do come in other types but
00:00:43.229 00:00:43.239 they're the two main ones and the
00:00:45.180 00:00:45.190 advantage of class 1 ceramic caps is
00:00:47.970 00:00:47.980 that they do not change with temperature
00:00:49.290 00:00:49.300 they're very very stable but they only
00:00:52.110 00:00:52.120 come in low values that's a major
00:00:53.880 00:00:53.890 disadvantage now the second type is
00:00:56.099 00:00:56.109 class 2 tire capacitors and there's more
00:00:58.200 00:00:58.210 varieties that you can poke a damn
00:00:59.880 00:00:59.890 sticker but some of the more common ones
00:01:02.189 00:01:02.199 you'll hear terms like X 7 or X 5 are y
00:01:05.460 00:01:05.470 5v z 5u and this is a code the first
00:01:09.420 00:01:09.430 character means it's the minimum
00:01:11.700 00:01:11.710 temperature in this case X is better
00:01:13.800 00:01:13.810 than Z the second character defines the
00:01:16.920 00:01:16.930 maximum temperature of the capacitor and
00:01:18.990 00:01:19.000 in this case a high numbers better 7s
00:01:20.940 00:01:20.950 better than 5 and the third digit is the
00:01:23.760 00:01:23.770 temperature coefficient how much change
00:01:26.039 00:01:26.049 in capacitance you get with that
00:01:27.810 00:01:27.820 temperature range and in this case R is
00:01:30.359 00:01:30.369 better than you are might be plus minus
00:01:32.990 00:01:33.000 15% but once you get down into V and you
00:01:36.749 00:01:36.759 the absolutely horrible minus 82 percent
00:01:39.179 00:01:39.189 minus 56 percent these things absolutely
00:01:41.940 00:01:41.950 shocking atrocious now generally ceramic
00:01:45.960 00:01:45.970 capacitors are known as multi-layer
00:01:47.940 00:01:47.950 capacitors due to their construction of
00:01:50.249 00:01:50.259 multi layers between the two end caps
00:01:52.709 00:01:52.719 and that's their more common term now
00:01:55.289 00:01:55.299 multi-layer chip capacitors ceramic
00:01:58.139 00:01:58.149 capacitors are used by their zillions
00:02:00.179 00:02:00.189 you can't count these things and they're
00:02:02.819 00:02:02.829 used for general purpose stuff like our
00:02:05.249 00:02:05.259 bypassing and filtering and things like
00:02:07.830 00:02:07.840 that because there's a whole grade and
00:02:09.359 00:02:09.369 whole variety of ceramic capacitors for
00:02:11.280 00:02:11.290 all these different purposes I'm a very
00:02:13.320 00:02:13.330 stable some are just absolutely
00:02:14.790 00:02:14.800 atrocious that you only use for you know
00:02:17.280 00:02:17.290 rough decoupling applications and things
00:02:19.380 00:02:19.390 like that
00:02:20.309 00:02:20.319 so it's very important to choose the
00:02:21.539 00:02:21.549 right type of ceramic capacity Cantor's
00:02:24.330 00:02:24.340 WAC any ceramic capacitor in there it
00:02:26.339 00:02:26.349 probably won't work now one weird thing
00:02:29.489 00:02:29.499 about class two ceramic capacitors
00:02:31.860 00:02:31.870 because of their because their ceramic
00:02:33.479 00:02:33.489 and the multi-layer construction they
00:02:36.300 00:02:36.310 are absent they are actually what's
00:02:38.369 00:02:38.379 called our microphonic due to the
00:02:41.670 00:02:41.680 piezoelectric effect any sound or
00:02:44.819 00:02:44.829 vibration in either directly into the
00:02:47.729 00:02:47.739 capital via the board can actually flex
00:02:50.429 00:02:50.439 it and it can generate a voltage just
00:02:52.860 00:02:52.870 like a microphone these things will
00:02:54.899 00:02:54.909 actually pick up and translate sound and
00:02:58.890 00:02:58.900 this phenomenon also works backwards so
00:03:02.550 00:03:02.560 if you drive this with a voltage add
00:03:05.280 00:03:05.290 some audio frequency or something like
00:03:07.530 00:03:07.540 that you can actually these things will
00:03:09.750 00:03:09.760 actually flex and they'll actually
00:03:11.520 00:03:11.530 generate sound and the PCB can be used
00:03:14.369 00:03:14.379 the PCB substrate can actually act as an
00:03:16.860 00:03:16.870 amplifier and these things can you can
00:03:18.750 00:03:18.760 actually hear these things it's it's
00:03:20.610 00:03:20.620 it's not fairly common but if you're
00:03:23.159 00:03:23.169 working on precision audio stuff this
00:03:26.490 00:03:26.500 can actually be quite important Oh micro
00:03:29.969 00:03:29.979 phonics watch out for it now this are
00:03:32.580 00:03:32.590 same microphonic phenomenon can also
00:03:35.219 00:03:35.229 happen in other caps like film caps as
00:03:37.259 00:03:37.269 well but not as much and it can also
00:03:39.059 00:03:39.069 happen in cables and other thinkers
00:03:41.550 00:03:41.560 because to remember cables or capacitors
00:03:43.979 00:03:43.989 to and they can have our micro phonics
00:03:47.759 00:03:47.769 and drive our electric effects as well
00:03:49.770 00:03:49.780 go and google that one a ceramic
00:03:51.929 00:03:51.939 capacitors are can fail short circuit
00:03:54.360 00:03:54.370 but they usually the main problem with
00:03:56.490 00:03:56.500 them is that they are very very brittle
00:03:58.830 00:03:58.840 very very fragile you can damage them
00:04:01.619 00:04:01.629 solder in on the board with excess
00:04:03.149 00:04:03.159 temperature handling and flex on the PCB
00:04:06.390 00:04:06.400 as well if you mount them in one
00:04:08.610 00:04:08.620 direction and you flex the board like
00:04:10.469 00:04:10.479 this you can actually crack they can get
00:04:11.999 00:04:12.009 micro cracks in them and that can be a
00:04:13.979 00:04:13.989 real problem for long term reliability
00:04:16.409 00:04:16.419 and things like that so just be very
00:04:18.569 00:04:18.579 very careful with how you mount and
00:04:20.849 00:04:20.859 handle multi-layer ceramic capacitors
00:04:23.490 00:04:23.500 right so that's the end of the
00:04:25.140 00:04:25.150 capacitors but I think we've got a
00:04:26.580 00:04:26.590 couple of seconds to explain an
00:04:28.230 00:04:28.240 important characteristic of capacitors
00:04:30.870 00:04:30.880 which is pretty neat and a lot of people
00:04:32.339 00:04:32.349 don't understand
00:04:33.270 00:04:33.280 now it's the impedance versus frequency
00:04:36.350 00:04:36.360 characteristic of a capacitor it's going
00:04:38.310 00:04:38.320 to look something like this
00:04:40.500 00:04:40.510 now the model of a capacitor is the ESR
00:04:43.560 00:04:43.570 in series with the capacitive reactance
00:04:45.750 00:04:45.760 which changes with frequency and the
00:04:48.360 00:04:48.370 inductive reactance as well which also
00:04:50.970 00:04:50.980 changes with frequency and this is the
00:04:52.410 00:04:52.420 total impedance so the graph is the
00:04:54.480 00:04:54.490 impedance versus the frequency and looks
00:04:57.330 00:04:57.340 like this now at low frequencies the the
00:05:00.660 00:05:00.670 actual capacitive reactance is going to
00:05:03.450 00:05:03.460 dominate and then at higher frequencies
00:05:06.360 00:05:06.370 the inductive reactance is going to take
00:05:09.540 00:05:09.550 over and that's going to dominate the
00:05:11.730 00:05:11.740 total impedance of the capacitor and
00:05:13.740 00:05:13.750 there's going to be a resonant point
00:05:15.360 00:05:15.370 here where these two things are equal
00:05:17.490 00:05:17.500 and you know and that's the best place
00:05:20.310 00:05:20.320 to operate the capacitor at in terms of
00:05:22.590 00:05:22.600 impedance now the important thing about
00:05:24.840 00:05:24.850 this is that it comes into play you've
00:05:27.240 00:05:27.250 probably seen multiple capacitors in
00:05:29.310 00:05:29.320 parallel all these different values
00:05:30.900 00:05:30.910 across a chip for decoupling and what
00:05:33.300 00:05:33.310 the reason they do this is because each
00:05:35.610 00:05:35.620 capacitor will have a different
00:05:37.740 00:05:37.750 characteristic like this each value so
00:05:40.890 00:05:40.900 your total will look something like that
00:05:44.910 00:05:44.920 and you get a much lower capacitance
00:05:47.040 00:05:47.050 over the entire frequency range and
00:05:49.560 00:05:49.570 that's why you put them in parallel it's
00:05:51.840 00:05:51.850 not as silly as it sounds it's actually
00:05:53.610 00:05:53.620 quite a valid technique that can gain
00:05:56.070 00:05:56.080 you quite a considerable performance in
00:05:58.800 00:05:58.810 terms of decoupling and EMI and things
00:06:01.110 00:06:01.120 like that so there you go ha that's it
00:06:05.070 00:06:05.080 there you go that's the end of
00:06:06.810 00:06:06.820 capacitors how do you choose a capacitor
00:06:09.120 00:06:09.130 I don't know don't ask me it's too
00:06:11.460 00:06:11.470 complicated Oh

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