Ray Wilson authored this content while he was actively running MFOS as the founder and resident genius.
We retain the content because it reflects a valuable point of view representing that time and place.

Article by Ray Wilson

Capacitors are passive electronic components that store electrical energy in the form of an electrostatic field. A capacitor consists of two conducting plates separated by an insulating material called the dielectric. Capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the separation between the plates. Capacitance also depends on the dielectric constant of the substance separating the plates. Capacitors are usually measured in microfarads abbreviated uF (1 uF = .000001 Farad) and picofarads, abbreviated pF (1 pF = .000000000001 F). Capacitors (or caps) are used in timers, filters, interstage coupling, power supplies, motors, etc. The working voltage of a capacitor is the voltage that can safely be applied without breaking down the dielectric material and causing the capacitor to short and be destroyed. When building a circuit be sure to buy caps that have a working voltage that is at least equal to or preferably somewhat above the highest voltage you plan to apply. Using caps with higher working voltage than you plan to apply is fine and is normally the case. Using caps with a lower voltage rating than you plan to apply is asking for trouble and can cause real damage if say you are using low working voltage caps in a power supply and one side of a supply becomes shorted due to a capacitor failure. In other cases capacitor shorts can result in complete loss of circuit function or degradation of circuit function. Caps come with ratings like 16V, 25V, 35V 50V etc. Size is another factor that comes into play as higher working voltage caps can be larger than their lower voltage counterparts. Most MFOS PC boards use a 0.2" lead spacing for the ceramic caps (which usually come in 25V to 100V working voltage). The electrolytic caps can vary and you should look at the PC board to see what will fit comfortably. Part leads are easy to form and as long as the board has room for them you can use whatever caps you can fit on the PC board. In other words when you find a super deal on a cap you want/need don't pass it up just because you may have to form the leads a bit to get it to fit on the board. The value of a cap can usually be changed by 10% or more and the circuit will still work perfectly. When a schematic calls for 0.002uF cap and all you can find is 0.0022uF cap don't panic it will work just fine (other examples: 0.02 specified 0.022 will again work fine, 0.03 specified 0.033 will work fine... etc.) Caps normally come with a tolerance of 10% to 20% so using a value very close to that specified in the schematic will normally not even be noticed in the final circuit's function. Of course if the circuit is some critical timing circuit then try to find the specified cap but ALL of the circuits shown on MFOS will be fine with cap changes in the 10% to 20% range with very little if any noticeable functional changes. A notable exception to the cap tolerance comments made above is when you are selecting caps for a two or four pole voltage controlled filter. Use caps that are as close to the values specified as possible in those cases because the function of the filter is improved by having matched caps in the filter's pole circuits. The closer the caps are to one another in value (typically the case in two or four pole filters) the better the filter will work. Use of a capacitance meter to measure and match your caps when making a VCF is definitely warranted. Use of temperature stable film caps is a good idea for VCFs and VCOs (polycarbonate or polystyrene). Always observe polarity markings when using polarized capacitors. In most cases the negative lead is marked with minus symbols but in others (tantalum caps for instance) there is a + symbol denoting the positive side. Another convention is that the positive lead is usually longer when you buy brand new caps but this may not be the case with surplus caps that have already had the leads trimmed or have been removed from equipment. Electrolytic polarized caps do not take kindly to having the voltage applied in the wrong polarity. Tantalum caps for instance will become leaky and useless if polarity is applied incorrectly. Tantalums can also go off like a firecracker (no exaggeration) sending shards flying. Aluminum electolytic caps will act like low value resistors and can burn out diodes in power supplies by drawing excessive current. Bipolar (or non-polarized) capacitors use aluminum electrolytic chemistry to get high capacitance but their plates are arranged so as to avoid polarization. They look very much like aluminum electrolytic caps but they will not have a plus symbol (+) or negative symbol (-) on the case. They may have the letters: BP or NP. When you are just starting out to buy your own components (weaning yourself from kits) I suggest you find caps at surplus houses like All Electronics at first so you get an inexpensive chance to see various caps and start to form a preference on the type and size you find most useful. Keep a notebook with parts and suppliers so that each time you order it becomes easier and takes less time. Many sites (Jameco, Mouser, etc) remember your previous orders and after a while ordering is simply re-ordering with the click of the mouse. Sometimes you need a capacitance value that you don't have on hand. You can put capacitors in series and/or parallel to produce different values. This image shows the formulas for obtaining values from capacitors by placing them in parallel (adding mode) or series (dividing mode). Placing caps in parallel essentially adds the plate areas together and voila higher capacitance. Placing caps in series essentially puts more space between the plates and voila lower capacitance (note it is always lower than the lowest value cap in series). A trick to remember for simulating "bipolar" or "non-polarized" caps is to use two polarized caps in series with the negative poles tied together. The values of course divide according to the series capacitance formula show below. When you use two capacitors with the same value the capacitance is simply divided in two.
The following chart may help you to convert capacitor values in one unit to a different unit. For example to convert from micro Farads to nano Farads you multiply the micro Farad value by one thousand (.001 micro Farad = 1 nano Farad). To convert micro Farads to pico Farads you multiply by one million. To convert nano Farads to pico Farads you multiply by one thousand. Capacitor value prefixes fall here in decimal representation. milli micro nano pico .000 000 000 000 .000 000 000 000 .000 000 000 000 .000 000 000 000 Some examples 1 Farad = 1,000,000 micro Farads or 1,000,000,000 nano Farads or 1,000,000,000,000 pico Farads. .001 Farad = 1,000 micro Farads or 1,000,000 nano Farads or 1,000,000,000 pico Farads. 1 micro Farad = 1,000 nano Farads or 1,000,000 pico Farads. .1 micro Farad = 100 nano Farads or 100,000 pico Farads. .01 micro Farad = 10 nano Farads or 10,000 pico Farads. .001 micro Farad = 1 nano Farad or 1,000 pico Farads. .0047 micro Farad = 4.7 nano Farad or 4,700 pico Farads. 47 nano Farads = 47,000 pico Farads. 4.7 nano Farads = 4,700 pico Farads. 2.2 nano Farads = 2,200 pico Farads.
	This is the schematic symbol for a non-polarized capacitor. You will also see them with one side as a curved line instead of being straight on both sides. These include ceramic, film and chip types. These types of caps may be inserted into a circuit without regard to orientation of the leads. They work the same in either direction. Typically the capacitance of these types ranges from a few picofarads to a couple of microfarads.
	These are all schematic symbols for polarized capacitors. You will also see them with one side as a curved line instead of being straight on both sides. These include aluminum electrolytic and tantalum caps. These types of caps must be inserted into a circuit with the proper lead orientation or bad things will happen. They DO NOT work the same in either direction. The capacitance of these types ranges from a few microfarads up to a farad (or larger). There is a type of aluminum cap that looks very much like a polarized aluminum cap that is known as a "non-polarized" or "bipolar" aluminum cap. These types do not have polarity markings and provide a lot of capacitance in a reasonably sized package where you need non-polarization.

Aluminum Electrolytic Capacitors As explained above these must be oriented properly when inserted into a circuit. They come in radial (both leads on the same end) and axial (leads on both ends) configurations. The lead configuration (axial or radial) makes no difference to the operation of the cap. They are clearly marked as to their capacitance, working voltage, and lead orientation. These types have higher leakage than tantalum caps. These are good for power supply filtering (10s of thousands of uFs) and power supply bypass caps (10 of uFs).

Aluminum Bipolar (Non-Polarized) Capacitors Bipolar (or non-polarized) capacitors use aluminum electrolytic chemistry to get high capacitance but their plates are arranged so as to avoid polarization. These capacitors do not need to be oriented in a particular way because of their non-polarization. They come in far higher values than are practical with ceramic or film type capacitors. They are excellent for passing AC signals while isolating DC. They will be marked as: BP or NP or Non-Polar and will not have polarity markings.

Polystyrene Capacitors Polystyrene capacitors are film capacitors and are the best choice for low leakage and good temperature stability. Be careful when soldering them and don't linger with your iron when installing them. They are excellent in VCOs, VCFs, and Sample and Hold circuits. They don't come in a wide range of values with 100pF to .01uF being about it.

Tantalum Capacitors Tantalum caps pack a lot of capacitance into a small space but beware to get the correct working voltage and to orient them properly. They will go off like fire crackers if reverse biased. As a matter of fact exposing a tantalum to reverse voltage as low as 1V can damage the cap over time leading to leakage and eventual short circuit. They are made of sintered tantalum, which provides a lot of nooks and crannies for surface area (thus the high capacitance in the small package). The dielectric is formed over the sintered pellet and then a conductive layer is applied. To be safe always use a bit higher working voltage then you intend to apply to the cap (x1.5 to x2.0 is a good safety factor). These types have relatively low leakage. They're good for ADSR timing caps (1 - 10 uF) and power supply bypass caps (10 of uFs). The longer lead is the positive lead (and/or the cap's + is marked).

Ceramic Disc Capacitors General-purpose non-polarized caps useful for power supply bypassing and for passing AC signals in interstage coupling. These range in value from a few pico-farads to several micro-farads. These can be conformally coated with many colors and can even appear to be a film capacitor.

Metallized Film Capacitors General-purpose non-polarized caps useful for power supply bypassing, passing AC signals in interstage coupling, filters, timers, oscillators, etc. Depending on the type you get these caps have very low leakage and good temperature stability. Types include: metallized film, polyester, polystyrene, mylar and polypropylene. These range in value from a few pico-farads to several micro-farads.

Reading Capacitor Values Sometimes the cap will plainly state its value like .01uF or .01M (meaning .01uF) but most of the time you will need to translate the value from something like 101 to 100pF using the accompanying chart. Remember that 1uF = .000001 farad or 1,000,000 picofarads. So to get the value for a cap remember this: 103 for example means 10 (and three zeroes) 000 or 10,000 pF or .01uF. 102 for example means 10 (and two zeroes) 00 or 1,000 pF or .001uF. 104 for example means 10 (and four zeroes) 0000 or 100,000 pF or .1uF.

For the number:	Multiply by:	LETTER	TOLERANCE 10pF or LESS	TOLERANCE OVER 10pF
0	1	B	+/- 0.1pF
1	10	C	+/-0.25pF
2	100	D	+/- 0.5pF
3	1000	F	+/- 1.0pF	+/- 1%
4	10,000	G	+/- 2.0pF	+/- 2%
5	100,000	H		+/- 3%
		J		+/- 5%
8	0.01	K		+/- 10%
9	0.1	M		+/- 20%