Monday, October 14, 2013
Introduction
All the methods developed so far for the analysis of linear resistive circuits are applicable to circuits that contain capacitors and inductors.
Unlike the resistor which dissipates energy, ideal capacitors and inductors store energy rather than dissipating it.
Capacitor
A capacitor is formed from two conducting plates separated by a thin
insulating layer.
If a current i flows, positive change, q, willaccumulate on the upper plate. To preserve
charge neutrality, a balancing negative charge
will be present on the lower plate.
Types of Capacitor
Capacitor symbol represents the two separatedplates. Capacitor types are distinguished by
the material used as the insulator.
Polystyrene: Two sheets of foil separated by a
thin plastic film and rolled up to save space.
Values: 10 pF to 1 nF.
Ceramic: Alternate layers of metal and ceramic
(a few μm thick). Values: 1 nF to 1 μF.
Electrolytic: Two sheets of aluminium foil
separated by paper soaked in conducting
electrolyte. The insulator is a thin oxide layer
on one of the foils. Values: 1 μF to 10mF.
Electrolytic capacitors are polarised: the foil with the oxide layer must
always be at a positive voltage relative to the other (else explosion).
Negative terminal indicated by a curved plate in symbol.
Inductors
Inductors are formed from coils of wire, often
around a steel or ferrite core.
Types of Inductors
As with many electrical devices, different models exist for
specific applications. Couples multilayer, ceramic core, and molded inductors
are all common types found in commercial and industrial applications:
Coupled Inductors
Coupled inductors exhibit magnetic flux that is dependent on
other to which they are linked. When mutual inductance is needed, coupled
inductors are often used. A transformer is a kind of coupled inductor.
Multi-Layer Inductors
This particular type of inductor consists of a layered coil,
wound multiple times around the core. As a result of the multiple layers and
the insulation between them, multi-layer inductors have a high inductance level.
Ceramic Core Inductors
Although there are numerous kinds of cores, a ceramic core
inductor is unique in having a dielectric ceramic core, meaning it cannot store
a lot of energy but has very low distortion and hysteresis.
Molded Inductors
These inductors are molded using plastic or ceramic
insulation. Often used in circuit boards, they can assume either a cylindrical
or bar formation, with windings featuring terminations at each end.
Formula
Capacitors
Parallel Capacitors
CT = C1 + C2 + C3 + … + Cn
Series Capacitors
CT = 1 / (1/C1 + 1/C2 + 1/C3 ... + 1/Cn)
Inductors
Series Inductance
LT = L1 + L2 + L3 + … + Ln
Parallel Inductance
LT = 1 / (1/L1 + 1/L2 + 1/L3 ... + 1/Ln)
