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About Capacitors

Word Origin and Invention Origin David Hazel:
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The first recorded capacitor originated in October 1745. Ewald von Kleist of Pomerania, Germany discovered that a glass jar plated inside and out with conductive metal and filled with water could be made to store an electric charge. Such a device is now called a Leyden Jar, after a Dutch physicist at the university of Leyden who made a similar discovery at the same time. Profile Picture David Hazel:
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A few years later, Benjamin Franklin discovered that by plating window panes on either side with conductive metal he could store an even stronger charge. These window panes were dubbed “Franklin Panes” and were the first flat capacitors. Benjamin also found that by connecting a large number of these panes in parallel he could store a quite significant static electric charge, which he theorized would be capable of killing small animals. Profile Picture David Hazel:
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Benjamin Franklin once tried to kill a turkey with his invention; releasing the turkey into a room, he then loaded a large panel of panes with charge and went after the bird; however, the turkey proved too hard to catch and Ben, accidentally touching the charge off on himself, blew himself across the small room. A word to the wise: be careful with large charges Profile Picture David Hazel:
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Capacitors were for some time called “condensers,” a term coined by Alessandro Volta in 1782, due to their ability to “condense” a charge in one place and store it. Profile Picture David Hazel:
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Synonyms: Condenser. Profile Picture David Hazel:
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Simple Explanation David Hazel:
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Capacitors are extremely simple devices. To illustrate, let's study a Franklin Pane, also called a parallel plate capacitor, the simplest type of capacitor. Profile Picture David Hazel:
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The pane looks like a sandwich & Profile Picture David Hazel:
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The charge difference between the plates is called electric potential, or voltage. Profile Picture David Hazel:
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Value Explained David Hazel:
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Capacitance is measured in units of farads. A farad describes the amount of charge a capacitor is capable of holding, and is defined by the surface area of a capacitor's charged plates, the distance between those plates, and a mathematical constant, called permittivity, describing the electrical qualities of the particular dielectric separating the plates. Profile Picture David Hazel:
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C David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.	= David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.	ε David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.	A David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
			d David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Where: David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.	C = capacitance (in farads) David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	ε = the absolute permittivity of the dielectric (in farads per meter; F/m) David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	A = surface area of each plate (in square meters) David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	d = distance between the plates (in meters) David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

And: Profile Picture David Hazel:
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David Hazel:
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ε_r

ε_o

Where: David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.	ε_o = 8.85 x 10^-12 = the absolute permittivity of free space (air) (units: F/m) David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	ε_r = the dielectric constant = the relative permittivity of the dielectric (unitless). David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

How large does a simple parallel plate capacitor have to be to reach a value of 1 farad? If our dielectric is air and we separate the plates by the thickness of a sheet of paper, we get an equation like this: Profile Picture David Hazel:
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1 David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.	= David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.	1(8.85 x 10^-12) David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.	A David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
			(1.016 x 10^-4) David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Solve that equation for A, and we get 11480226 square meters, or approximately 4.4 square miles! Profile Picture David Hazel:
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Most capacitors used in circuit boards are much smaller than one farad, and are often measured in micro, nano, and pico farads. It takes one million micro farads, or one billion nano farads, or one trillion pico farads to make one farad. Profile Picture David Hazel:
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Units David Hazel:
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Capacitance is measured in units of farads, designated by the Arabic letter, “F”. A farad describes the amount of charge a capacitor is capable of holding. But you already knew that if you browsed the “Value Explained” section above. Profile Picture David Hazel:
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Here is a breakdown of the farad unit of measure: Profile Picture David Hazel:
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(A x s)

C²

(s² x C²)

(s⁴ x A²)

(N x m)

(m² x kg)

Where: David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.	F = Farads David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	A = Amps David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	s = Seconds David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	V = Volts David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	C = Coulombs David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	J = Joules David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	N = Newtons David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	m = Meters David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.
	kg = Kilograms David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Kinds of Capacitors and their Uses David Hazel:
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Electrolytic - Made of electrolyte, basically conductive salt in solvent. Aluminum electrodes are used by using a thin oxidation membrane. Most common type, polarized capacitor. Applications: Ripple filters, timing circuits. Cheap, readily available, good for storage of charge (energy). Not very accurate, marginal electrical properties, leakage, drifting, not suitable for use in hf circuits, available in very small or very large values in uF. They WILL explode if the rated working voltage is exceeded or polarity is reversed, so be careful. When you use this type capacitor in one of your projects, the rule-of-thumb is to choose one which is twice the supply voltage. Example, if your supply power is 12 volt you would choose a 24volt (25V) type. This type has come a long way and characteristics have constantly improved over the years. It is and always will be an all-time favorite; unless something better comes along to replace it. But I don't think so for this decade; polarized capacitors are heavily used in almost every kind of equipment and consumer electronics. Tony Van Roon:
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Tantalum - Made of Tantalum Pentoxide. They are electrolytic capacitors but used with a material called tantalum for the electrodes. Superior to electrolytic capacitors, excellent temperature and frequency characteristics. When tantalum powder is baked in order to solidify it, a crack forms inside. An electric charge can be stored on this crack. Like electrolytics, tantalums are polarized so watch the '+' and '-' indicators. Mostly used in analog signal systems because of the lack of current-spike-noise. Small size fits anywhere, reliable, most common values readily available. Expensive, easily damaged by spikes, large values exists but may be hard to obtain. Largest in my own collection is 220uF/35V, beige color. Tony Van Roon:
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Super Tony Van Roon:
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Tony Van Roon really knows his stuff. He's been teaching this stuff (profesionally and as a hobby) for longer than some of us have been alive. He has earned our respect, and we don't hesitate to show it. These capacitors achieve extremely high capacitance values for their size by using (often) nanotechnology and have extremely porous, high surface-area electrodes. For example, David Hazel:
David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again. the Electric Double Layer capacitor is a real miracle piece of work. Capacitance is 0.47 Farad (470,000 uF). Despite the large capacitance value, its physical dimensions are relatively small. It has a diameter of 21 mm (almost an inch) and a height of 11 mm (1/2 inch). Like other electrolytics the super capacitor is also polarized so exercise caution in regards to the break-down voltage. Care must be taken when using this capacitor. It has such large capacitance that, without precautions, it would destroy part of a powersupply such as the bridge rectifier, volt regulators, or whatever because of the huge inrush current at charge. For a brief moment, this capacitor acts like a short circuit when the capacitor is charged. Protection circuitry is a must for this type. Tony Van Roon:
Tony Van Roon really knows his stuff. He's been teaching this stuff (profesionally and as a hobby) for longer than some of us have been alive. He has earned our respect, and we don't hesitate to show it. These capacitors can in some cases be used in place of rechargeable batteries. David Hazel:
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Polyester Film - This capacitor uses a thin polyester film as a dielectric. Not as high a tolerance as polypropylene, but cheap, temperature stable, readily available, widely used. Tolerance is approx 5% to 10%. Can be quite large depending on capacity or rated voltage and so may not be suitable for all applications. Tony Van Roon:
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Polypropylene - Mainly used when a higher tolerance is needed then polyester caps can offer. Polypropylene film is the dielectric. Very little change in capacitance when these capacitors are used in applications within frequency range 100KHz. Tolerance is about 1%. Very small values are available. Tony Van Roon:
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Polystyrene - Is used as a dielectric. Constructed like a coil inside so not suitable for high frequency applications. Well used in filter circuits or timing applications using a couple hundred KHz or less. Electrodes may be reddish of color because of copper leaf used or silver when aluminum foil is used for electrodes. Tony Van Roon:
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Metalized Polyester Film - Dielectric made of Polyester or DuPont trade name "Mylar". Good quality, low drift, temperature stable. Because the electrodes are thin they can be made very very small. Good all-round capacitor. Tony Van Roon:
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Epoxy - Manufactured using an epoxy dipped polymers as a protective coating. Widely available, stable, cheap. Can be quite large depending on capacity or rated voltage and so may not be suitable for all applications. Tony Van Roon:
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Ceramic - Constructed with materials such as titanium acid barium for dielectric. Internally these capacitors are not constructed as a coil, so they are well suited for use in high frequency applications. Typically used to by-pass high frequency signals to ground. They are shaped like a disk, available in very small capacitance values and very small sizes. Together with the electrolytics the most widely available and used capacitor around. Comes in very small size and value, very cheap, reliable. Subject to drifting depending on ambient temperature. NPO types are the temperature stable types. They are identified by a black stripe on top. Tony Van Roon:
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Multilayer Ceramic - Dielectric is made up of many layers. Small in size, very good temperature stability, excellent frequency stable characteristics. Used in applications to filter or bypass the high frequency to ground. They don't have a polarity. *Multilayer caps suffer from high-Q internal (parallel) resonances - generally in the VHF range. The CK05 style 0.1uF/50V caps for example resonate around 30MHz. The effect of this resonance is effectively no apparent capacitance near the resonant frequency.
As with all ceramic capacitors, be careful bending the legs or spreading them apart to close to the disc body or they may get damaged. Tony Van Roon:
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Silver-Mica - Mica is used as a dielectric. Used in resonance circuits, frequency filters, and military RF applications.
Highly stable, good temperature coefficient, excellent for endurance because of their frequency characteristics, no large values, high voltage types available, can be expensive but worth the extra dimes. Tony Van Roon:
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Adjustable Capacitors - Also called trimmer capacitors or variable capacitors. It uses ceramic or plastic as a dielectric. Most of them are color coded to easily recognize their tunable size. The ceramic type has the value printed on them. Colors are: yellow (5pF), blue (7pF), white (10pF), green (30pF), brown (60pf). There are a couple more colors like red, beige, and purple which are not listed here Tony Van Roon:
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Tuning or 'air-core' capacitors - These use the surrounding air as a dielectric. I have seen these variable capacitor types of incredible dimensions, especially the older ones. Amazing it all worked. Mostly used in radio and radar equipment. This type usually have more (air) capacitors combined (ganged) and so when the adjustment axel is turned, the capacitance of all of them changes simultaneously. The one on the right has a polyester film as a dielectric constant and combines two independent capacitors plus included is a trimmer cap, one for each side. Tony Van Roon:
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Paper - was used extensively in older devices and offers relatively high voltage performance. However, it is susceptible to water absorption, and has been largely replaced by plastic film capacitors. Wikipedia:
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Glass - extremely reliable, stable and tolerant to high temperatures and voltages, but highly expensive. Wikipedia:
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Varicap or Varactor Diodes - These Wikipedia:
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Dielectrics David Hazel:
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Dielectrics are electrical insulators, they stop the flow of electrons. After reading the simple explanation of a capacitor, above, you now know that a dielectric layer is at the center of every capacitor. Dielectrics of various types all have different electrical and chemical properties. If the voltage across the conductive plates in a capacitor reaches a certain level, called the dielectric breakdown voltage, it will literally rip the atoms of the dielectric apart, the dielectric will start conducting, and the capacitor will fail, sometimes catastrophically (explosion or general destruction of the part) depending on the dielectric in question. Profile Picture David Hazel:
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Dielectric properties can also be affected by temperature, and they can age and change over time. Profile Picture David Hazel:
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Dielectric Codes David Hazel:
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this content Profile Picture Mehile "Mo" Orloff:
Mehile Orloff is one of the founding members of VCI, and has been an integral part of our growth from the beginning.

is under Profile Picture Mehile "Mo" Orloff:
Mehile Orloff is one of the founding members of VCI, and has been an integral part of our growth from the beginning.

development Profile Picture Mehile "Mo" Orloff:
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"NPO" is standard for temperature stability and 'low-noise', it does *not* mean non-polarized even though you might think so because the abbreviation looks similar. Polarized ceramic capacitors do not exist. The abbreviation "NPO" stands for "Negative-Positive-Zero" (what is read as an 'O' is actually zero), and means that the negative and positive temperature coefficients of the device are zero--that is the capacitance does not vary with temperature. ONLY the black top indicates NPO qualification and the values are in the range from 1.8pF to 120pF, unless manufactured with different values for Military and/or industrial purposes on special request. They feature 2% tolerance which comes down to about 0.25pF variation, and all are 100V types. You may sometimes find NPO-type caps marked with the EIA (Electronic Industrial Association) code "COG". The EIA has an established set of specifications for capacitor temperature characteristics (EIC 384/class 1B). Thus, a capacitor labeled "Y5P" would exhibit a plus/minus tolerance of 10% variation in capacitance over a temperature range of -30°C. to +85°C. Or it may say N12 which translates to 120pF. Or 2P2 (2.2pF). I'm sure you get the idea & Profile Picture Tony Van Roon:
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But the average hobbyist uses only a couple types like the common electrolytic and general purpose ceramic capacitors and depending on the application, a more temperature stable type like metal-film or polypropylene. Profile Picture Tony Van Roon:
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The larger the plate area and the smaller the separation between the plates, the larger the capacitance. Which also depends on the type of insulating material between the plates, which is the smallest with air. (You see this type of capacitor sometimes in high-voltage circuits and are called 'spark-caps'.) Replacing the air space with an insulator will increase the capacitance many times over. The capacitance ratio using an insulator material is called Dielectric Constant while the insulator material itself is called just Dielectric. Using the table in Fig. 4, if a Polystyrene dielectric is used instead of air, the capacitance will be increased 2.60 times. Profile Picture Tony Van Roon:
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Fig.4 Dielectric Constant of Materials Tony Van Roon: Tony Van Roon really knows his stuff. He's been teaching this stuff (profesionally and as a hobby) for longer than some of us have been alive. He has earned our respect, and we don't hesitate to show it.
Air Tony Van Roon: Tony Van Roon really knows his stuff. He's been teaching this stuff (profesionally and as a hobby) for longer than some of us have been alive. He has earned our respect, and we don't hesitate to show it.	1.00 Tony Van Roon: Tony Van Roon really knows his stuff. He's been teaching this stuff (profesionally and as a hobby) for longer than some of us have been alive. He has earned our respect, and we don't hesitate to show it.	Glass Tony Van Roon: Tony Van Roon really knows his stuff. He's been teaching this stuff (profesionally and as a hobby) for longer than some of us have been alive. He has earned our respect, and we don't hesitate to show it.	7.75 Tony Van Roon: Tony Van Roon really knows his stuff. He's been teaching this stuff (profesionally and as a hobby) for longer than some of us have been alive. He has earned our respect, and we don't hesitate to show it.	Polystyrene Tony Van Roon: Tony Van Roon really knows his stuff. He's been teaching this stuff (profesionally and as a hobby) for longer than some of us have been alive. He has earned our respect, and we don't hesitate to show it.	2.6 Tony Van Roon: Tony Van Roon really knows his stuff. He's been teaching this stuff (profesionally and as a hobby) for longer than some of us have been alive. He has earned our respect, and we don't hesitate to show it.
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Dielectric Aging Wikipedia:
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The capacitance of certain capacitors decreases as the component ages. In ceramic capacitors, this is caused by degradation of the dielectric. The type of dielectric and the ambient operating and storage temperatures are the most significant aging factors, while the operating voltage has a smaller effect. The aging process may be reversed by heating the component above the Curie point. For many capacitors, aging is fastest near the beginning of life of the component, and the device stabilizes over time. Electrolytic capacitors age as the electrolyte evaporates. In contrast with ceramic capacitors, this occurs towards the end of life of the component. Wikipedia:
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In addition to baking, soldering is often an effective de-aging process. Profile Picture David Hazel:
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Voltage Explained David Hazel:
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Electric potential, or voltage, is similar to any other form of potential energy. Let's compare it to a water tower; in a water tower, you pump water high up into the air and store it in an elevated reservoir. The water then has a long distance that it can fall; and if released, by the time the water reaches the ground it has the potential to generate a high amount of force, enough force to pressurize all of the water faucets in town, this is a form of mechanical potential energy. Electrical potential energy is no different, except we call it voltage, and the “water” in this case is electrons. To release and use that potential energy, all we have to do is give electrons the opportunity to flow “down hill” from a place of higher charge to a place of lower charge. Profile Picture David Hazel:
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Tolerances Explained David Hazel:
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Capacitors, like other passive electronic components, come in different tolerances. What is a tolerance? Manufacturing processes are never perfect, so the manufacturers will guarantee that the capacitors they sell fall within a certain range of the expected value, this range is called the part's tolerance, and is often expressed in a percentage. Profile Picture David Hazel:
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Value tolerances used to be marked on the capacitor in percentage. An older cap might be marked as ".05 10%", meaning 0.05fF, 10%. Newer caps use a letter for the tolerance, and that will seem confusing right at first. A common value might be ".1M" which means 0.1fF, 20%. A little newer cap might be marked as "332K" and that drives some folks nuts. After all, "K" is a standard metric prefix multiplier and they automatically think they have a 332,000fF cap on their hands. In reality, they have a 3300pF (33 + 2 zeros, in pF) with a ±10% tolerance. The letters on these caps correspond to the following list. I've marked the tolerances that you'll find to be the most common with an asterisk. Profile Picture Tony Van Roon:
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B = ±0.1pF C = ±0.25pF D = ±0.5pF E = ±0.25% F = ±1.0% G = ±2% H = ±2.5% J = ±5% * K = ±10% *

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L	=	±15%
M	=	±20%	*
N	=	±30%
P	=	-0, +100%
S	=	-20, +50%
W	=	-0, +200%
X	=	-20, +40%
Z	=	-20, +80%	*

You'll find that the "Z" tolerance of -20, +80% to be common for aluminum electrolytic caps and for disc ceramic caps that are used for what is known as "bulk capacitance" in applications such as power supply bypassing or filtering. These kinds of capacitors are used where it's OK for the value to be a lot larger than nominal, but they don't want it to go very far below that value. Profile Picture Tony Van Roon:
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If you do a lot of analog circuit design and building where you attempt to get frequency-dependent circuits to be as accurate as possible, you'll see or want to find Mylar caps with a "G" or "F" tolerances of ±2% or ±1% respectively. They're harder to find in catalogs, but if you watch the electronics surplus catalogs, you can find then on a sporadic basis. The tolerances of "B" through "E" are in pF vs. percent and are normally used on small caps of around 10pF or less. Profile Picture Tony Van Roon:
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Capacitor Markings David Hazel:
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I guess you would really like to know how to read all those different codes. Not to worry, it is not as difficult as it appears to be. Except for the electrolytic and large types of capacitors, which usually have the value printed on them like 470uF 25V or something, most of the smaller caps have two or three numbers printed on them, some with one or two letters added to that value. Check out the little table below. Profile Picture David Hazel:
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Fig.2 Capacitor Value Codes
3rd Digit	Multiplier
0	1
1	10
2	100
3	1,000
4	10,000
5	100,000
6 & 7	Not Used
8	.01
9	.1

Fig.3 Capacitor Value Codes
Letter	Tolerance
D	0.5pF
F	1%
G	2%
H	3%
J	5%
K	10%
M	20%
P	+100%, -0%
Z	+80%, -20%

So, for example, it you have a ceramic capacitor with 474J printed on it it means: 47+4zeros = 470000 = 470,000pF, J=5% tolerance. (470,000pF = 470nF = 0.47uF) Pretty simple, huh? The only major thing to get used to is to recognize if the code is uF nF, or pF. Profile Picture David Hazel:
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Other capacitors may just have 0.1 or 0.01 printed on them. If so, this means a value in uF. Thus 0.1 means just 0.1 uF. If you want this value in nanoFarads just move the comma three places to the right which makes it 100nF. Easy huh? Profile Picture David Hazel:
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Capacitor Circuit Symbols David Hazel:
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Capacitors in schematics are represented as a pair of plates. Sometimes the plates are drawn as straight lines (a), sometimes as curved ones (d), and sometimes as a combination of the two. Past electronic magazines such as Radio Electronics, Hands-on Electronics, and Popular Electronics used the symbols in fig. (a), (d), (c), and (g). While european magazines such as the Dutch Elektuur (Elektor) uses symbols as depicted in (a), (e), and (f). Profile Picture Tony Van Roon:
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Symbol in (c) is a variable capacitor like a trimmer cap, and (g) is a ganged variable capacitor such as a air-plate capacitor as used in radios. Profile Picture Tony Van Roon:
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Electrolytic capacitors are frequently indicated by a symbol with one straight and one curved line (d) or the european way of drawing this symbol in (e). A '+' sign is placed at the straight line to indicate the anode. Occasionally an electrolytic is drawn as two straight lines, but the plus sign is always included to indicate its polarity. Profile Picture Tony Van Roon:
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When a capacitor is shown as one straight line and one curved one, the curved line, which represents the outer case or electrode of the device, is assumed to be at a lesser potential than the straight one. Thus, since signal flow in a schematic diagram is usually from left to right, capacitors are drawn with their curved ends facing left or, if that is not possible, facing down, which is the direction usually used to represent ground. Electrolytics, especially, are depicted with the curved place facing downward.
Variable capacitors are usually depicted as shown in (c) and (f). The arrow is the conventional symbol used to indicate that a device may be adjusted over a range of values. A multi-section variable device may be shown with one symbol for each section, with dashed lines (g) to show that both of the sections are ganged together. Profile Picture Tony Van Roon:
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In schematics, capacitor values are usually indicated in microFarads unles a note specifies that things are otherwise. Voltage ratings, if they are given, are usually indicated in microFarads (uF) unless a note specifies that things are otherwise. Voltage ratings, if they are given, are usually presented as part of a "fraction." A label of "4.7uF/35V" or "4.7/35" would indicate a capacitor with a value of 4.7uF with a a working voltage of 35 volts. Profile Picture Tony Van Roon:
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MicroFarads are indicated with the greek letter 'u' (µ). Don't make the mistake of writing uF as mF. 'm' Stands for 'milli' and is definately not the same. Profile Picture Tony Van Roon:
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Capacitors and Frequency David Hazel:
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Up until this point we have only talked about how capacitors behave in simple direct current (DC) situations. When the circuit they are in contains an electronic frequency capacitors have many very useful characteristics; in particular, if the frequency is high enough, a capacitor will conduct it and let that frequency pass right through, while preventing the rest of the current from escaping; in this way, capacitors are useful for filtering noise (high frequency garbage) off of digital circuit boards, this is called “bypassing,” or “decoupling.” Profile Picture David Hazel:
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The phrase "bypass" or "decoupling" is referred to filtering noise off the power rails caused by switching of TTL IC's, MosFets, Transistors, etc. Especially TTL (Transistor-Transistor-Logic) IC's create a lot of noise and so this has to be cleaned up. Mounting a 100nF (0.1uF) ceramic bypass capacitor over the power rails and as close to the IC as possible and keeping the capacitor leads as short as you can, will clean up noise nicely. This has to be done on all IC's and power rails on a printed circuit board with this kind of digital logic. Noise can cause all sorts of problems such as false triggering, cross-talk, change to an undesirable logic state, etc. Decoupling is used where the supply voltage cannot be lowered, i.e., if one needed a noise free +12V on a PC bus, for example. You could get a "clean" +12 volts with a voltage regulator... if only there was +15 volts or higher to start with. But such is not the case. So you use a high "Q" inductor or RFC choke along with the proper bypass capacitor to effectively lowpass filter the +12 volt supply rail. For a real noisy supply you can use more than one inductor: a "pie" network for example. Profile Picture Tony Van Roon:
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As digital becomes faster and faster, it looks more like analog than digital. It would be an asset to have a good understanding of the analog/rf properties of high speed digital. Careful layout of a groundplane and proper decoupling and bypass requires close attention of a circuit design to maintain the integrity of the power distribution. Profile Picture Tony Van Roon:
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Decoupling / Bypassing Suggestions David Hazel:
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Excessive lead length will void the purpose of a bypass capacitor so keep the leads short. Profile Picture Tony Van Roon:
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If needed, attempt the following as stated below. Profile Picture Tony Van Roon:
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Tony Van Roon:
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Use 0.1uF (=100nanoF) or greater, ceramic capacitor, surface mount technology or SMT preferred.
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One capacitor per SSI, MSI TTL, device.
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The capacitors should be connected over the Vcc and Gnd with the shortest path possible.
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Ceramic disc capacitors have the best high frequency characteristics and the least self inductance.
Tony Van Roon:
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Only in RF applications it is appropriate to mix different type caps together to filter at different freq's.
Tony Van Roon:
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Substituting a tantalum for a ceramic type will not work, but they can work together very well.

Equations and Formulas David Hazel:
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Is it possible to combine capacitors to get to a certain value like we do with resistors?
Certainly! Check below how go about it. Profile Picture David Hazel:
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Capacitors in Parallel Profile Picture Tony Van Roon:
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Capacitors connected in parallel, which is the most desirable, have their capacitance added together, which is just the opposite of parallel resistors. It is an excellent way of increasing the total storage capacity of an electric charge: Profile Picture David Hazel:
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C_total = C₁ + C₂ + C₃

Keep in mind that only the total capacitance changes, not the supplied voltage. Every single capacitor will see the same voltage, no matter what. Be careful not to exceed the specified voltage on the capacitors when combining them all with different voltage ratings, or they may explode. Example: say you have three capacitors with voltages of 16V, 25V, and 50V. The voltage must not exceed the lowest voltage, in this case the 16V one. As a matter of fact, and a rule-of-thumb, always choose a capacitor which is twice the supplied input voltage. Example: If the input voltage is 12V you would select a 24V type (in real life 25V). Profile Picture David Hazel:
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Capacitors in Series Profile Picture Tony Van Roon:
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Again, just the opposite way of calculating resistors. Multiple capacitors connected in series with each other will have the total capacitance lower than the lowest single value capacitor in that circuit. Not the preferred method but acceptable. Profile Picture Tony Van Roon:
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For the capacitors connected in series above, use the following formula: Profile Picture David Hazel:
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1	=	1	+	1	+	1
C_total	=	C₁	+	C₂	+	C₃

Direct Current (DC) David Hazel:
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Electrons flowing in one direction is called direct current. Direct current in a wire is very similar to water flowing through a pipe, electrons enter at one end, flow down the wire, and exit at the other end. Profile Picture David Hazel:
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In the early days of electric power people tried to transmit electricity via direct current, but they soon discovered that the electricity wouldn't travel very far. No matter how good they are, wires all resist the flow of electrons to some degree, so the farther you get from the power source the less electricity will come out of the wire. Profile Picture David Hazel:
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Direct current becomes dangerous as the current (flow of electrons) increases. Try turning a water hose on all the way and squirt the water at some dirt. The water will blast a hole into the dirt. Electrons are the same way; if you have enough of them flowing at once, they will blast holes through molecules, this often takes the form of a burn. Be careful with large charges and high voltages! Profile Picture David Hazel:
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Alternating Current (AC) David Hazel:
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When electrons move back and forth this is called alternating current because the flow (current) of electrons regularly alternates direction. In an AC circuit, most of the electrons never leave the wire, they move back and forth in the same way that you move your hand when you scrub the floor. Profile Picture David Hazel:
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Today, all of our house wiring and power lines run on alternating current. If you watch a light bulb, it continuously has the same electrons scrubbing back and forth across it to produce light. AC current can transmit much much farther than DC current because it travels down the wire via an electro-magnetic wave. Profile Picture David Hazel:
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Alternating Current is more dangerous than Direct Current. Thomas Edison tried to get high voltage alternating current outlawed, making his point in several demonstrations where he killed large animals, including an elephant at Luna Park Zoo in 1903. AC is dangerous precisely because it alternates and at high enough voltages can overpower the electrical signals that control heart beat, literally stopping the heart. Profile Picture David Hazel:
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About Capacitors

Word Origin and Invention Origin David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Simple Explanation David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Value Explained David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Units David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Kinds of Capacitors and their Uses David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Dielectrics David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Dielectric Codes David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Dielectric Aging Wikipedia: Undoubtedly, you already know how usefull wikipedia can be.

Voltage Explained David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Tolerances Explained David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Capacitor Markings David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Capacitor Circuit Symbols David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Capacitors and Frequency David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Decoupling / Bypassing Suggestions David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Equations and Formulas David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Direct Current (DC) David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

Alternating Current (AC) David Hazel: David Hazel has been a key player for VCI since April of 2008. Not only is he a blast to have around the shop, but as our inhouse engineer, his knowledge and skill-sets have proven invaluable time and time again.

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Components, Inc.