Equivalent Series Inductance (ESL)

The equivalent series inductance is the parasitic longitudinal inductance of a capacitor, caused by the design (inductance of the foil windings).

Real capacitors do not only show a capacitance C, but also still parasitic effects. These undesirable parasitic properties are indicated by the equivalent series inductance (ESL) and the equivalent series resistance (ESR).

For capacitors, the ESL is particularly noticeable at high frequencies, e.g. with switched mode power supplies. This is due to the fact that the capacitive resistance drops by 10 dB/decade with increasing frequency, while the inductive resistance rises by 10 dB/decade.
In the higher frequency range, the inductive resistance can be greater than the capacitive resistance of an electrolytic capacitor: The capacitor then becomes the inductance.

To reduce these undesired effects at higher frequencies, the ESL must be minimized. Back