Practical considerations
Inductors, like all electrical components,
have limitations which must be respected for the sake of
reliability and proper circuit operation.
Rated current: Since inductors are
constructed of coiled wire, and any wire will be limited in
its current-carrying capacity by its resistance and ability
to dissipate heat, you must pay attention to the maximum
current allowed through an inductor.
Equivalent circuit: Since inductor
wire has some resistance, and circuit design constraints
typically demand the inductor be built to the smallest
possible dimensions, there is not such thing as a "perfect"
inductor. Inductor coil wire usually presents a substantial
amount of series resistance, and the close spacing of wire
from one coil turn to another (separated by insulation) may
present measurable amounts of stray capacitance to interact
with its purely inductive characteristics. Unlike
capacitors, which are relatively easy to manufacture with
negligible stray effects, inductors are difficult to find in
"pure" form. In certain applications, these undesirable
characteristics may present significant engineering
problems.
Inductor size: Inductors tend to be
much larger, physically, than capacitors are for storing
equivalent amounts of energy. This is especially true
considering the recent advances in electrolytic capacitor
technology, allowing incredibly large capacitance values to
be packed into a small package. If a circuit designer needs
to store a large amount of energy in a small volume and has
the freedom to choose either capacitors or inductors for the
task, he or she will most likely choose a capacitor. A
notable exception to this rule is in applications requiring
huge amounts of either capacitance or inductance to
store electrical energy: inductors made of superconducting
wire (zero resistance) are more practical to build and
safely operate than capacitors of equivalent value, and are
probably smaller too.
Interference: Inductors may affect
nearby components on a circuit board with their magnetic
fields, which can extend significant distances beyond the
inductor. This is especially true if there are other
inductors nearby on the circuit board. If the magnetic
fields of two or more inductors are able to "link" with each
others' turns of wire, there will be mutual inductance
present in the circuit as well as self-inductance, which
could very well cause unwanted effects. This is another
reason why circuit designers tend to choose capacitors over
inductors to perform similar tasks: capacitors inherently
contain their respective electric fields neatly within the
component package and therefore do not typically generate
any "mutual" effects with other components. |