EEVblog #33 1of2 - Capacitor Tutorial (Electrolytic, Tantalum, & Plastic Film)

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hi this blog is going to be all about
00:00:13.030 00:00:13.040 capacitors the what why how and where of
00:00:16.540 00:00:16.550 using capacitors I've got ten minutes
00:00:19.750 00:00:19.760 let's start now okay the first type of
00:00:24.170 00:00:24.180 capacitor is the electrolytic capacitor
00:00:26.990 00:00:27.000 you've seen them before these things in
00:00:28.730 00:00:28.740 the metal cans they've basically got an
00:00:31.100 00:00:31.110 aluminium foil in them filled with a
00:00:33.139 00:00:33.149 liquid electrolyte and these things are
00:00:36.560 00:00:36.570 absolutely horrible they are all full
00:00:39.439 00:00:39.449 capacities in in almost every respect
00:00:42.400 00:00:42.410 try and avoid using them if you can but
00:00:45.680 00:00:45.690 the problem is the advantage of them is
00:00:48.049 00:00:48.059 that they come in massive capacitance
00:00:51.139 00:00:51.149 values for their size so really yeah you
00:00:54.559 00:00:54.569 really can't avoid using them for things
00:00:56.899 00:00:56.909 like power supply filtering and large
00:01:00.380 00:01:00.390 bypassing and things like that and in
00:01:02.689 00:01:02.699 power storage and some AC coupling
00:01:05.840 00:01:05.850 applications for very low frequencies
00:01:07.820 00:01:07.830 it's hard to avoid these things so
00:01:09.649 00:01:09.659 unfortunately there are necessary evil
00:01:11.840 00:01:11.850 you've almost certainly noticed this
00:01:14.209 00:01:14.219 little vent mark on the top this is
00:01:16.580 00:01:16.590 actually a pressure vent that in the
00:01:18.679 00:01:18.689 case of these things overheating and
00:01:20.389 00:01:20.399 overloading
00:01:22.100 00:01:22.110 the vent is supposed to break and
00:01:23.630 00:01:23.640 release the energy so that they don't
00:01:25.219 00:01:25.229 explode and our foil goes everywhere
00:01:27.469 00:01:27.479 well they don't always work these
00:01:29.630 00:01:29.640 suckers can explode they're dangerous be
00:01:31.880 00:01:31.890 careful one of the hugest problems with
00:01:34.550 00:01:34.560 these things is that they dry out over
00:01:37.190 00:01:37.200 time heat can kill these things the
00:01:39.620 00:01:39.630 liquid in there dries out and this
00:01:41.330 00:01:41.340 increases the equivalent series
00:01:43.069 00:01:43.079 resistance the ESR and really to measure
00:01:46.969 00:01:46.979 this you've got to have an ESR meter not
00:01:49.760 00:01:49.770 a capacitance meter an ESR meter I use
00:01:52.039 00:01:52.049 this Bob Parker one thumbs up you've got
00:01:54.529 00:01:54.539 to have something like this if you want
00:01:56.270 00:01:56.280 to test electrolytic because the life of
00:01:58.580 00:01:58.590 these things is inversely proportional
00:02:00.520 00:02:00.530 to the temperature they use that so the
00:02:03.349 00:02:03.359 higher the temperature the shorter the
00:02:05.270 00:02:05.280 life now these will have a rated life on
00:02:08.690 00:02:08.700 the datasheet at a certain temperature
00:02:10.669 00:02:10.679 but you can easily shorten that life if
00:02:13.430 00:02:13.440 you mount this thing near a heat sink or
00:02:16.220 00:02:16.230 something like that inside your product
00:02:17.839 00:02:17.849 these things need to be kept
00:02:19.870 00:02:19.880 cool but don't make them too cool
00:02:21.760 00:02:21.770 because then their their ESR just shoots
00:02:23.860 00:02:23.870 through the roof of cold temperatures
00:02:25.210 00:02:25.220 they're horrible high ESR on these
00:02:27.820 00:02:27.830 things is probably the number one
00:02:29.710 00:02:29.720 failure mode in consumer products if
00:02:32.410 00:02:32.420 you're plasma TV fails or your digital
00:02:35.590 00:02:35.600 set-top box or DVD player fails it's
00:02:37.990 00:02:38.000 probably because one of these has dried
00:02:40.330 00:02:40.340 out in the power supply odds-on now if
00:02:43.780 00:02:43.790 you want the best reliability for
00:02:45.340 00:02:45.350 electrolytic capacitors you need to
00:02:47.290 00:02:47.300 stick to the name-brand ones and check
00:02:49.930 00:02:49.940 the data sheets and use the high quality
00:02:52.720 00:02:52.730 ones
00:02:53.080 00:02:53.090 there's tons of fake ones and dodgy ones
00:02:55.900 00:02:55.910 on the market and you can get duped into
00:02:58.510 00:02:58.520 it another major problem with these
00:03:00.760 00:03:00.770 things is that they have a maximum ah
00:03:03.270 00:03:03.280 charge and discharge or ripple current
00:03:05.980 00:03:05.990 they can handle so make sure you read
00:03:08.410 00:03:08.420 the data sheets and you don't exceed
00:03:10.390 00:03:10.400 that ripple current because if you do
00:03:12.760 00:03:12.770 they can heat up internally and like I
00:03:15.580 00:03:15.590 said shorten the life if you want really
00:03:17.710 00:03:17.720 reliable designs using these things you
00:03:20.020 00:03:20.030 put two or more in parallel that way
00:03:22.540 00:03:22.550 they share the ripple current they share
00:03:24.310 00:03:24.320 the heat and they lower the ESR and it
00:03:27.700 00:03:27.710 increases your liability and system so
00:03:30.360 00:03:30.370 parallel is a really good way to go and
00:03:32.890 00:03:32.900 you can also get low ESR versions of
00:03:35.860 00:03:35.870 these things and they're good for use in
00:03:38.500 00:03:38.510 switch mode power suppliers and low
00:03:40.840 00:03:40.850 dropout voltage regulators and things
00:03:42.760 00:03:42.770 like that now the temperature variation
00:03:45.370 00:03:45.380 of electrodes is pretty horrible can be
00:03:47.200 00:03:47.210 anywhere from plus 5 to minus 40% minus
00:03:50.680 00:03:50.690 50% so just watch out for it and of
00:03:53.800 00:03:53.810 course they're polarized you have to put
00:03:55.780 00:03:55.790 them in your circuit the right way
00:03:57.160 00:03:57.170 that's a major disadvantage now they
00:04:00.790 00:04:00.800 have a maximum reverse voltage of about
00:04:02.830 00:04:02.840 1.5 volts anything over that continuous
00:04:05.980 00:04:05.990 and you're going to damage these things
00:04:07.540 00:04:07.550 permanently sometimes you're going to
00:04:09.250 00:04:09.260 need a non polarized electrolytic
00:04:11.740 00:04:11.750 capacitor and you can't actually buy
00:04:14.230 00:04:14.240 them but if you haven't got one you can
00:04:16.510 00:04:16.520 do it by putting two in series
00:04:19.120 00:04:19.130 back-to-back like this with the two
00:04:21.520 00:04:21.530 negatives together or the two positives
00:04:23.800 00:04:23.810 together it doesn't matter which way
00:04:24.970 00:04:24.980 around sometimes in high voltage
00:04:26.740 00:04:26.750 applications you need to put two
00:04:30.700 00:04:30.710 electrolytic capacitors in
00:04:32.159 00:04:32.169 Cirie's it's not recommended but if you
00:04:34.200 00:04:34.210 have to you can do it got to capacitors
00:04:37.170 00:04:37.180 like this one of them could leak very
00:04:39.179 00:04:39.189 badly and that will change the voltage
00:04:41.580 00:04:41.590 division ratio and you'll get excess
00:04:43.860 00:04:43.870 voltage across one of the capacitors and
00:04:45.779 00:04:45.789 that can quickly destroy it so what you
00:04:48.269 00:04:48.279 do is you put ballast resistors
00:04:50.159 00:04:50.169 across the two caps and you calculate
00:04:52.739 00:04:52.749 these values based on the worst-case
00:04:54.649 00:04:54.659 leakage current of one of the capacitors
00:04:57.209 00:04:57.219 and the maximum voltage that that
00:04:59.339 00:04:59.349 capacitor can handle the other thing
00:05:01.890 00:05:01.900 about electrolytic capacitors is a
00:05:03.989 00:05:03.999 phenomenon called dielectric absorption
00:05:05.959 00:05:05.969 and this means that the capacitor can
00:05:09.059 00:05:09.069 actually rebuild its charge after you've
00:05:11.610 00:05:11.620 shorted it you know 1020 percent
00:05:13.619 00:05:13.629 recovery something like that so in high
00:05:15.989 00:05:15.999 voltage applications that can actually
00:05:17.369 00:05:17.379 be dangerous so be wary of it next up we
00:05:20.640 00:05:20.650 have tantalum capacitors these things
00:05:23.249 00:05:23.259 these little resin dipped ones or the
00:05:25.529 00:05:25.539 surface mount tantalum caps and these
00:05:28.140 00:05:28.150 are another necessary evil in a lot of
00:05:31.409 00:05:31.419 cases you avoid using them if you can
00:05:33.809 00:05:33.819 the first problem with tandems is that
00:05:35.730 00:05:35.740 the tantalum material itself is actually
00:05:37.679 00:05:37.689 a fairly rare metal it requires lots of
00:05:40.350 00:05:40.360 mining and this can lead to very high
00:05:43.110 00:05:43.120 prices and shortage of tantalum ah if
00:05:46.950 00:05:46.960 you use quite a few years back there's a
00:05:48.629 00:05:48.639 huge tantalum shortage in the market
00:05:50.909 00:05:50.919 simply marketing to complete and utter
00:05:52.950 00:05:52.960 chaos and they're talking about it
00:05:54.570 00:05:54.580 happening again soon the other major
00:05:56.730 00:05:56.740 problem with tandems is that they're
00:05:58.230 00:05:58.240 famous for blowing up and bursting into
00:06:01.260 00:06:01.270 flames the damn things are flammable and
00:06:03.239 00:06:03.249 this is generally considered a bad thing
00:06:06.350 00:06:06.360 tantalum is also just like Electro's
00:06:08.969 00:06:08.979 they hate high pulse and ripple currents
00:06:11.760 00:06:11.770 so watch the datasheet and don't go
00:06:13.829 00:06:13.839 anywhere near those limits but it's not
00:06:16.559 00:06:16.569 all doom and gloom with Tanna lumps they
00:06:18.119 00:06:18.129 do have some good aspects if you use
00:06:20.279 00:06:20.289 them with inside their specs they're
00:06:21.869 00:06:21.879 actually very reliable much more
00:06:24.209 00:06:24.219 reliable than Electro's in some cases
00:06:26.010 00:06:26.020 but just like Electro's they're they're
00:06:27.959 00:06:27.969 pretty horrible caps generally all right
00:06:30.570 00:06:30.580 they're they're very low leakage though
00:06:31.860 00:06:31.870 that's another good thing about them but
00:06:33.450 00:06:33.460 you'll generally find them in just
00:06:34.950 00:06:34.960 pretty much power supply decoupling and
00:06:37.110 00:06:37.120 large value uh energy reserves things
00:06:40.499 00:06:40.509 like that
00:06:41.279 00:06:41.289 you're very common for FPGA decoupling
00:06:44.070 00:06:44.080 these days that now there are
00:06:45.870 00:06:45.880 different types of tan limbs these days
00:06:48.540 00:06:48.550 as the technology gets better organic
00:06:50.640 00:06:50.650 and polymer tatum's and look at using
00:06:53.400 00:06:53.410 those as substitutes but they're rarer
00:06:55.260 00:06:55.270 and more expensive now thankfully the
00:06:57.930 00:06:57.940 ceramic technology these days is eating
00:07:00.450 00:07:00.460 away the need to have tantalum
00:07:02.850 00:07:02.860 capacitors now another type of main
00:07:04.950 00:07:04.960 capacitor are these film capacitors
00:07:07.320 00:07:07.330 plastic film capacitors and they come in
00:07:10.050 00:07:10.060 two major types one of the main types of
00:07:12.450 00:07:12.460 plastic film capacitors are the
00:07:14.280 00:07:14.290 polyester type there are general-purpose
00:07:16.110 00:07:16.120 ones you use for bypassing AC coupling
00:07:18.960 00:07:18.970 filtering applications things like that
00:07:21.000 00:07:21.010 you can get quite stable ones their main
00:07:22.980 00:07:22.990 advantages that they have a high
00:07:24.900 00:07:24.910 capacitance per unit volume due to their
00:07:28.380 00:07:28.390 high dissipation factor you wouldn't use
00:07:30.300 00:07:30.310 polyester in high poles high current or
00:07:33.480 00:07:33.490 high frequency applications at the other
00:07:35.730 00:07:35.740 major type of cap is polypropylene now
00:07:38.460 00:07:38.470 these have much higher performance due
00:07:40.440 00:07:40.450 to their lower dissipation factor and
00:07:42.180 00:07:42.190 their higher dielectric strength you use
00:07:44.520 00:07:44.530 them for high voltage high frequency
00:07:46.710 00:07:46.720 high current pulse applications and
00:07:49.410 00:07:49.420 things like that so really grunty
00:07:51.150 00:07:51.160 capacitors but their major disadvantages
00:07:53.580 00:07:53.590 you can only get them in small values
00:07:55.860 00:07:55.870 here's a good tip polypropylene and
00:07:58.260 00:07:58.270 polyester capacitors have roughly
00:08:00.590 00:08:00.600 opposite temperature characteristics so
00:08:03.870 00:08:03.880 if you actually put the two in two types
00:08:06.000 00:08:06.010 in parallel you can get a reasonably
00:08:08.010 00:08:08.020 stable or a much more stable temperature
00:08:11.340 00:08:11.350 characteristic the other major type of
00:08:13.740 00:08:13.750 film capacitor is the polyethylene
00:08:15.750 00:08:15.760 sulfide and these are mainly used in SMD
00:08:18.930 00:08:18.940 caps because the other ones are mainly
00:08:20.310 00:08:20.320 through-hole and these are very stable
00:08:22.680 00:08:22.690 and close tolerance caps now the other
00:08:25.890 00:08:25.900 type of capacitor out there is a mica
00:08:28.680 00:08:28.690 and these are very exotic kind of things
00:08:31.530 00:08:31.540 that are used really for only ultra high
00:08:33.719 00:08:33.729 stability ultra close tolerance
00:08:36.330 00:08:36.340 applications so if you need a mica
00:08:39.330 00:08:39.340 you're going to know it I can't do this
00:08:41.279 00:08:41.289 blog without mentioning mains rated
00:08:44.120 00:08:44.130 capacitors now you can't just use any
00:08:47.280 00:08:47.290 old capacitor when you're hooking these
00:08:49.440 00:08:49.450 things directly on the mains for like
00:08:51.270 00:08:51.280 suppression these special mains Raider
00:08:53.010 00:08:53.020 ones come in two different types two
00:08:54.870 00:08:54.880 different classes Class X and class Y
00:08:57.360 00:08:57.370 now Class X
00:08:59.110 00:08:59.120 comes in two types x1 and x2 x1 are
00:09:02.560 00:09:02.570 rated for higher voltage higher pulse
00:09:05.880 00:09:05.890 applications but either can be used
00:09:07.930 00:09:07.940 generally and they are designed x-class
00:09:10.900 00:09:10.910 are designed to go directly across the
00:09:13.030 00:09:13.040 mains they're not designed for anywhere
00:09:16.150 00:09:16.160 that can be accessed by people something
00:09:18.940 00:09:18.950 for safety and things like that
00:09:20.590 00:09:20.600 that's where class y comes in class Y
00:09:23.320 00:09:23.330 capacitors are used between either of
00:09:26.140 00:09:26.150 the mains lines and protective earth and
00:09:28.690 00:09:28.700 you've got to make sure you use the
00:09:30.160 00:09:30.170 right type and these the advantage of
00:09:33.010 00:09:33.020 these capacitors is that they're
00:09:34.300 00:09:34.310 self-healing what it means is that if
00:09:36.610 00:09:36.620 you get a tiny little overload and spark
00:09:38.769 00:09:38.779 inside the capacitor basically what it
00:09:41.320 00:09:41.330 does is itself extinguishes itself and
00:09:44.050 00:09:44.060 just breaks it and you lose a tiny
00:09:45.940 00:09:45.950 amount of capacitance miniscule but it
00:09:48.310 00:09:48.320 means the thing doesn't overload or
00:09:50.019 00:09:50.029 short or explode or something like that
00:09:52.360 00:09:52.370 and you've got to make sure you use
00:09:54.310 00:09:54.320 these right type of capacitors if you
00:09:56.410 00:09:56.420 don't your products won't get approved
00:09:58.480 00:09:58.490 and they can kill someone
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