Parasitic element (electrical networks)

In

electrical component but which it is not desirable for it to have for its intended purpose. For instance, a resistor is designed to possess resistance, but will also possess unwanted parasitic capacitance

.

Parasitic elements are unavoidable. All conductors possess resistance and inductance and the principles of duality ensure that where there is inductance, there will also be capacitance. Component designers will strive to minimise parasitic elements but are unable to eliminate them. Discrete components will often have some parasitic values detailed on their datasheets to aid circuit designers in compensating for unwanted effects.

The most commonly seen manifestations of parasitic elements in components are in the parasitic inductance and resistance of the component leads and the parasitic capacitance of the component packaging. For wound components such as

windings. This winding parasitic capacitance will cause the inductor to act as a resonant circuit

at some frequency, known as the self-resonant frequency, at which point (and all frequencies above) the component is useless as an inductor.

Parasitic elements are often modelled as

distributed element along the whole length of the winding and not a capacitor in one particular place. Designers sometimes take advantage of parasitic effects to achieve a desired function in a component, see for instance helical resonator or analog delay line

.

Nonlinear parasitic elements can also arise. The term is commonly used to describe

non-linear effects

that vary with frequency or voltage and cannot be adequately modelled by linear lumped or distributed components.

References

John L. Semmlow, Circuits, signals, and systems for bioengineers, pp. 134–135, Academic Press, 2005
ISBN 0-12-088493-3
.

Steven H. Voldman, ESD: Failure Mechanisms and Models, pp. 13–14, John Wiley and Sons, 2009
ISBN 0-470-51137-0
.