Instruct: Given a question, retrieve documents that answer the question.
Query: What is the most common use for capacitors?
A capacitor can store electric energy when it is connected to its charging circuit. And when it is disconnected from its charging circuit, it can dissipate that stored energy, so it can be used like a temporary battery. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents loss of information in volatile memory.)
Ceramic capacitors come in various shapes and styles. Some of the most common are:
Filter capacitors are capacitors used for filtering of undesirable frequencies. They are common in electrical and electronic equipment, and cover a number of applications, such as:
The early style of the ceramic disc capacitor could be more cheaply produced than the common ceramic tube capacitors in the 1950s and 1970s. An American company in the midst of the Apollo program, launched in 1961, pioneered the stacking of multiple discs to create a monolithic block. This "multi-layer ceramic capacitor" (MLCC) was compact and offered high-capacitance capacitors. The production of these capacitors using the tape casting and ceramic-electrode cofiring processes was a great manufacturing challenge. MLCCs expanded the range of applications to those requiring larger capacitance values in smaller cases. These ceramic chip capacitors were the driving force behind the conversion of electronic devices from through-hole mounting to surface-mount technology in the 1980s. Polarized electrolytic capacitors could be replaced by non-polarized ceramic capacitors, simplifying the mounting.
As of 2012, only five plastic materials continued to be widely used in the capacitor industry as films for capacitors: PET, PEN, PP, PPS and PTFE. Other plastic materials are no longer in common use, either because they are no longer manufactured, or they have been replaced with better materials. Even the long-time manufactured polystyrene (PS) and polycarbonate (PC) film capacitors have been largely replaced by the previously-mentioned film types, though at least one PC capacitor manufacturer retains the ability to make its own films from raw polycarbonate feedstock. The less-common plastic films are described briefly here, since they are still encountered in older designs, and are still available from some suppliers.
Film capacitors for use in electronic equipment are packaged in the common and usual industry styles: axial, radial, and SMD. Traditional axial type packages are less used today, but are still specified for point-to-point wiring and some traditional through-hole printed circuit boards. The most common form factor is the radial type (single ended), with both terminals on one side of the capacitor body. To facilitate automated insertion, radial plastic film capacitors are commonly constructed with terminal spacings at standardized distances, starting with 2.5 mm pitch and increasing in 2.5 mm steps. Radial capacitors are available potted in plastic cases, or dipped in an epoxy resin to protect the capacitor body against environmental influences. Although the transient heat of reflow soldering induces high stress in the plastic film materials, film capacitors able to withstand such temperatures are available in Surface Mounted Device“ (SMD) packages.
One of the great advantages of plastic films for capacitor fabrication is that plastic films have considerably fewer defects than paper sheets used in paper capacitors. This allows the manufacture of plastic film capacitors with only a single layer of plastic film, whereas paper capacitors need a double layer of paper. Plastic film capacitors were significantly smaller in physical size (better volumetric efficiency), with the same capacitance value and the same dielectric strength as comparable paper capacitors. Then-new plastic materials also showed further advantages compared with paper. Plastic is much less hygroscopic than paper, reducing the deleterious effects of imperfect sealing. Additionally, most plastics are subject to fewer chemical changes over long periods, providing long-term stability of their electrical parameters. Since around 1980, paper and metallized paper capacitors (MP capacitors) have almost completely been replaced by PET film capacitors for most low-power DC electronic applications. Paper is now used only in RFI suppression or motor run capacitors, or as a mixed dielectric combined with polypropylene films in large AC and DC capacitors for high-power applications.
The physical form and construction of practical capacitors vary widely and many capacitor types are in common use. Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy.
The use of rotating synchronous condensers was common through the 1950s. They remain an alternative (or a supplement) to capacitors for power factor correction because of problems that have been experienced with harmonics causing capacitor overheating and catastrophic failures. Synchronous condensers are also useful for supporting voltage levels. The reactive power produced by a capacitor bank is in direct proportion to the square of its terminal voltage, and if the system voltage decreases, the capacitors produce less reactive power, when it is most needed, while if the system voltage increases the capacitors produce more reactive power, which exacerbates the problem. In contrast, with a constant field, a synchronous condenser naturally supplies more reactive power to a low voltage and absorbs more reactive power from a high voltage, plus the field can be controlled. This reactive power improves voltage regulation in situations such as when starting large motors, or where power must travel long distances from where it is generated to where it is used, as is the case with "power wheeling", the transmission of electric power from one geographic region to another within a set of interconnected electric power systems.
The most common kinds of capacitors are:In addition to the above shown capacitor types, which derived their name from historical development, there are many individual capacitors that have been named based on their application. They include:Often, more than one capacitor family is employed for these applications, e.g. interference suppression can use ceramic capacitors or film capacitors.
Capacitors, together with resistors, and inductors, belong to the group of "passive components" used in electronic equipment. Although, in absolute figures, the most common capacitors are integrated capacitors (e.g. in DRAMs or flash memory structures), this article is concentrated on the various styles of capacitors as discrete components.
A vacuum variable capacitor is a variable capacitor which uses a high vacuum as the dielectric instead of air or other insulating material. This allows for a higher voltage rating than an air dielectric using a smaller total volume. However, many dielectrics have higher breakdown field strengths than vacuum: 60-170 MV/m for teflon, 470-670 MV/m for fused silica and 2000 MV/m for diamond, compared with 20-40 MV/m for vacuum. There are several different designs in vacuum variables. The most common form is inter-meshed concentric cylinders, which are contained within a glass or ceramic vacuum envelope, similar to an electron tube. A metal bellows is used to maintain a vacuum seal while allowing positional control for the moving parts of the capacitor.
Solid tantalum capacitors can also withstand reverse voltages for short periods. The most common guidelines for tantalum reverse voltage are:
These guidelines apply for short excursion and should never be used to determine the maximum reverse voltage under which a capacitor can be used permanently.
The most important group is the fixed capacitors. Many got their names from the dielectric. For a systematic classification these characteristics can't be used, because one of the oldest, the electrolytic capacitor, is named instead by its cathode construction. So the most-used names are simply historical.
The dielectric films, depending on the desired dielectric strength, are drawn in a special process to an extremely thin thickness, and are then provided with electrodes. The electrodes of film capacitors may be metallized aluminum or zinc applied directly to the surface of the plastic film, or a separate metallic foil. Two of these conductive layers are wound into a cylinder shaped winding, usually flattened to reduce mounting space requirements on a printed circuit board, or layered as multiple single layers stacked together, to form a capacitor body. Film capacitors, together with ceramic capacitors and electrolytic capacitors, are the most common capacitor types for use in electronic equipment, and are used in many AC and DC microelectronics and electronics circuits.
Porcelain was used in the first ceramic capacitors. In the early years of Marconi's wireless transmitting apparatus porcelain capacitors were used for high voltage and high frequency application in the transmitters. On the receiver side smaller mica capacitors were used for resonant circuits. Mica dielectric capacitors were invented in 1909 by William Dubilier. Prior to World War II, mica was the most common dielectric for capacitors in the United States.[14]
Capacitors (often referred to as "caps") have several uses in electric guitars, the most common of which is in the tone control, where it combines with the potentiometer to form a low-pass filter, shorting all frequencies above the adjustable cut-off frequency to ground. Another common use is a small capacitor in parallel with the volume control, to prevent the loss of higher frequencies as the volume pot is turned down. This capacitor is commonly known as "treble bleed cap" and is sometimes accompanied by a series or parallel resistor to limit the amount of treble being retained and match it to the pot's taper.
Since capacitors differ in their high-frequency characteristics (and capacitors with good high-frequency properties are often types with small capacity, while large capacitors usually have worse high-frequency response), decoupling often involves the use of a combination of capacitors. For example in logic circuits, a common arrangement is ~100 nF ceramic per logic IC (multiple ones for complex ICs), combined with electrolytic or tantalum capacitor(s) up to a few hundred μF per board or board section.
Even in the early years of Marconi's wireless transmitting apparatus, porcelain capacitors were used for high voltage and high frequency application in the transmitters. On the receiver side, the smaller mica capacitors were used for resonant circuits. Mica dielectric capacitors were invented in 1909 by William Dubilier. Prior to World War II, mica was the most common dielectric for capacitors in the United States.
Most capacitors have numbers printed on their bodies to indicate their electrical characteristics. Larger capacitors like electrolytics usually display the actual capacitance together with the unit, for example, 220 μF. Smaller capacitors like ceramics, however, use a shorthand-notation consisting of three digits and a letter, where the digits indicate the capacitance in pF, calculated as XY × 10Z for digits XYZ, and the letter indicates the tolerance. Common tolerance indications are J, K, and M for ±5%, ±10%, and ±20%, respectively.
Most power capacitors, the largest capacitors made, generally use polypropylene film as the dielectric. PP film capacitors are used for high-frequency high-power applications such as induction heating, for pulsed power energy discharge applications, and as AC capacitors for electrical distribution. The AC voltage ratings of these capacitors can range up to 400 kV.
A decoupling capacitor is a capacitor used to protect one part of a circuit from the effect of another, for instance to suppress noise or transients. Noise caused by other circuit elements is shunted through the capacitor, reducing the effect they have on the rest of the circuit. It is most commonly used between the power supply and ground. An alternative name is bypass capacitor as it is used to bypass the power supply or other high impedance component of a circuit.
Last but not least the electric double-layer capacitor (now Supercapacitors) were invented. In 1957 H. Becker developed a "Low voltage electrolytic capacitor with porous carbon electrodes".[14][15][16] He believed that the energy was stored as a charge in the carbon pores used in his capacitor as in the pores of the etched foils of electrolytic capacitors. Because the double layer mechanism was not known by him at the time, he wrote in the patent: "It is not known exactly what is taking place in the component if it is used for energy storage, but it leads to an extremely high capacity."
Tantalum electrolytic capacitors with solid manganese dioxide electrolyte are limited by ripple current and generally have the highest ESR ratings in the capacitor family. Exceeding their ripple limits can lead to shorts and burning parts. Aluminum electrolytic capacitors, the most common type of electrolytic, suffer a shortening of life expectancy at higher ripple currents. If ripple current exceeds the rated value of the capacitor, it tends to result in explosive failure. Ceramic capacitors generally have no ripple current limitation and have some of the lowest ESR ratings. Film capacitors have very low ESR ratings but exceeding rated ripple current may cause degradation failures.
Ceramic capacitors, especially multilayer ceramic capacitors (MLCCs), are the most produced and used capacitors in electronic equipment that incorporate approximately one trillion (10) pieces per year.