Encyclopedia Capacitor

A capacitor is an electrical component that can store energy in the form of an electric field. For this purpose, two electrically conductive bodies (electrodes) are brought into a position in which they are opposite each other without any electrical contact. The electric field can build up between them, the electrically insulating material in which the field is located is called dielectric. A prerequisite for the electric field is a potential difference between the two conducting bodies, i.e. an electric Voltage between them.

The characteristic quantity for a capacitor is its capacitance. The capacitance is a measure of how much energy must be expended to reach a certain voltage (e.g. 1 volt). It is said that the capacitor is charged to a voltage. The capacitance of a capacitor depends on the mechanical construction, namely the spacing of the electrodes and their area, and the properties of the dielectric are also essential.

Apart from being used as short-term energy storage devices, capacitors are mainly used as frequency-dependent devices. This allows one to build filters that have a frequency-dependent passband curve, which is used, for example, in Crossovers.

Depending on the application, one uses capacitors with different designs and technologies, which have their respective advantages and disadvantages. In the hi-fi sector, the following types are found above all (there are other, but less significant types):

Aluminum electrolytic capacitors

Here, one electrode is formed by an aluminum foil, the other electrode consists of a conductive liquid, the electrolyte (hence the name "electrolytic capacitor" - short Elko). In between is a dielectric of aluminium oxide, which forms a thin layer on the aluminium foil. The aluminium foil is often chemically roughened to increase the surface area. This design results in large electrode area and very small electrode spacing, which provides a large capacitance with a fairly small mechanical size of the component. Elkos are suitable therefore if it depends on as large a capacity as possible. A disadvantage is that they are polarized, i.e. the voltage may only be applied in one direction, because if the voltage is reversed, the dielectric would decompose under the influence of the electrolyte, rendering the capacitor useless. Elcaps also tend to dry out slowly over a long period of time, especially when operated at high temperature. Their service life is therefore limited.

Elcaps are found in virtually all devices, especially for filtering (smoothing) the operating voltage in the power supply, and often in the signal path as coupling capacitors - here the filtering effect is used to separate DC voltage.

Ceramic capacitors

Here the dielectric consists of a ceramic, which carries the electrodes as metallizations. A large number of different types of ceramics exist, giving the capacitors very different properties. Ceramics with a high dielectric constant allow a large capacitance in a small space, although not to the order of electrolytic capacitors, but these ceramics are highly nonlinear, meaning their properties change significantly with temperature and applied voltage. Other ceramics are very linear but have relatively low dielectric constant and are only suitable for relatively small capacitances.

This type is used for interference suppression, where high frequencies have to be dissipated, or for suppression of oscillation tendencies. In the signal path, only the linear types come into question, and there the achievable capacitance is often too low.

Foil capacitors

Here the capacitor consists of a plastic or paper foil as dielectric. The electrodes are either metal vapor deposited on the foil, or they are separate metal foils wound together with the dielectric foil. The properties of these types depend greatly on the dielectric material. Linearity is typically very good, so the capacitors are well suited for signal path applications. However, for large capacitances, the capacitor quickly becomes relatively large and expensive.

These types are used in filters, and generally all applications where they are in the signal path.

See also:

• Wikipedia article: capacitor