Information

28
2 Capacitor Characteristics
2.1 Capacitance of a capacitor
2.1.1 Dependence on voltage
By applying a voltage, some insulators used in capacitors as dielectric experience a
change in permittivity ε
r
and consequently a reduction in capacitance. This can be
explained in the case of the dielectrics mentioned here in that once a specific voltage
is applied to the electrodes, a defined polarization of the molecules occurs. This
reduces the permittivity ε
r
of the material or dielectric.
Fig. 2.1: Voltage-dependent capacitance change, example: ceramic capacitors
2.1.2 Dependence on frequency
Capacitor types exist for which a frequency-dependent change in permittivity ε
r
occurs.
Generally the capacitance of a capacitor drops when the voltage applied increases.
This can be illustrated with the example of an X2 film capacitor in which polypropylene
is used as the dielectric. The graph in Figure 2.2 shows the percentage change in
capacitance over the frequency band from 1 kHz to 100 kHz.
–100
–60
–70
–80
–90
–50
–40
10
–30
–20
–10
0
0101520253035
54
0
DC voltage (V)
Capacitance change ∆C/C
0
(%)
NP0
X7R
X5R
Y5V