Lexikon Kondensator specifications

Category : Lexicon

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 lie opposite each other without there being 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, that is, an electric voltage between them.

The characteristic quantity for a capacitor is its capacitance. Capacitance is a measure of how much energy must be expended to reach a certain voltage (e.g. 1 volt). This is referred to as charging the capacitor to a voltage. The capacitance of a capacitor depends on the mechanical design, namely on the distance of the electrodes and their area, and the properties of the dielectric are also essential.

In addition to being used as short-term energy storage devices, capacitors are mainly used as a frequency-dependent component. As a result, it is possible to build filters that have a frequency-dependent transmission curve, which is used, for example, in crossovers.

Depending on the application, capacitors with different designs and technologies are used, which have their respective advantages and disadvantages. In the Hi-fi sector, you will find the following types in particular (there are other, but less significant types):

Here, one electrode is formed by an aluminum foil, the other electrode consists of a conductive liquid, the electrolyte (hence the name "electrolytic capacitor" - Elko for short). Between them there is a dielectric of aluminum oxide, which forms as a thin layer on the aluminum foil. The aluminum foil is often chemically roughened to increase the surface area. This design results in a large electrode area and very small electrode spacings, which offers a large capacitance with a rather small mechanical size of the component. Electrolytic capacitors are therefore suitable when it comes to the largest possible capacity. It can be considered as a disadvantage that they are polarized, so the voltage may only be applied in one direction, because if the voltage is reversed, the dielectric would decompose under the action of the electrolyte, as a result of which the capacitor becomes unusable. Electrolytic capacitors also tend to dry out slowly over a long period of time, especially if they are operated at high temperature. Their service life is therefore limited.

Electrolytic capacitors can be found in practically all devices, especially for screening (smoothing) the operating voltage in the power supply, and often also in the signal path as coupling capacitors - here the filtering effect is used to separate DC voltage.

Here, the dielectric consists of a ceramic that carries the electrodes as metallizations. There are a large number of different types of ceramics, which give 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 magnitude of electrolytic capacitors, but these ceramics are highly nonlinear, that is, their properties change significantly with temperature and the applied voltage. Other ceramics are very linear, but have a relatively low dielectric constant and are only suitable for relatively small capacitances.

This type is used for interference suppression, where it is about the dissipation of high frequencies, or for the suppression of oscillatory inclinations. In the signal path, only the linear types are suitable, and the achievable capacitance is often too low there.

The capacitor here consists of a plastic or paper film as a dielectric. The electrodes are either made of metal vapor-deposited on the foil or they are separate metal foils which are wound together with the dielectric foil. The properties of these types are highly dependent on the dielectric material. The linearity is typically very good, the capacitors are therefore well suited for applications in the signal path. However, with large capacities, the capacitor quickly becomes relatively large and expensive.

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