electrical network An electrical network is an interconnection of electrical components (e.g., batteries, resistors, inductors, capacitors, switches, transistors) or a model of such an interconnection, consisting of electrical elements (e.g., voltage sources ...

s, a parasitic element is a circuit element ( resistance, inductance or

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized ar ...

) that is possessed by an

electrical component An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not ...

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

inductor An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a c ...

s and

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

s, there is additionally the important effect of parasitic capacitance that exists between the individual turns of the

winding An electromagnetic coil is an electrical conductor such as a wire in the shape of a coil (spiral or helix). Electromagnetic coils are used in electrical engineering, in applications where electric currents interact with magnetic fields, in de ...

s. This winding parasitic capacitance will cause the inductor to act as a

resonant circuit An LC circuit, also called a resonant circuit, tank circuit, or tuned circuit, is an electric circuit consisting of an inductor, represented by the letter L, and a capacitor, represented by the letter C, connected together. The circuit can ac ...

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 lumped components in equivalent circuits, but this is not always adequate. For instance, the inter-winding capacitance mentioned above is really a distributed element along the whole length of the winding and not a

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

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 An analog delay line is a network of electrical components connected in cascade, where each individual element creates a time difference between its input and output. It operates on analog signals whose amplitude varies continuously. In the c ...

. Nonlinear parasitic elements can also arise. The term is commonly used to describe parasitic structures formed on an integrated circuit whereby an unwanted semiconductor device is formed from p-n junctions which belong to two or more intended devices or functions. The parasitic effects in the

dielectric In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...

of capacitors and parasitic magnetic effects in inductors also include 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 . *Steven H. Voldman, ''ESD: Failure Mechanisms and Models'', pp. 13–14, John Wiley and Sons, 2009 {{ISBN, 0-470-51137-0. Electronic design Distributed element circuits