Information

23
1 Basic Principles
1.8 Capacitor
The area A is determined from the length L and width W of the electrodes:
A = L * W (1.12)
The capacitance C is calculated from the field constant ε
0
, the relative permittivity ε
r
of the dielectric used, the effective area A (the overlapping area of the electrodes) and
the thickness d of the dielectric or the separation produced between the electrodes.
The field pattern within an ideal plate capacitor is homogeneous, so that the electric
field prevailing in the plate capacitor is of the same magnitude at every point of the
field and is uniform throughout. The capacitor types used in modern electronics largely
correspond with the principle structure of a plate capacitor.
A capacitor, as an electronic component, is able to store electrical energy and to
release it again. The energy release takes place at a defined rate over a certain period
depending on its design characteristics.
A capacitor is an energy reservoir, which blocks the direct flow of current with DC
voltage and allows the flow of current with AC or pulsating voltage depending on its
capacitance and the given frequency. So the capacitor can assume a different role
depending on the circuit:
• in a DC circuit it is a charge storage device
• in an AC circuit it is a frequency-dependent resistor
How much energy a capacitor has stored can be determined from the following
formula:
E
==
C * V
2
2
C * U
2
2
(1.13)
On account of its above properties, the capacitor is an indispensable component in to-
day’s electronics. Approximately two-thirds of the passive component market volume is
attributable to capacitors. The market for capacitors in relation to sales encompassed
a total volume of approximately 13 bn. € in 2012.
Energy