Stores energy in the form of magnetic field and delivers it as and when required. Whenever current passes through a conductor, lines of magnetic flux are generated around it. This magnetic flux opposes any change in current due to the induced e.m.f. This opposition to the current is known as inductance and the component producing inductance is known as inductor.
Unit Henry (H).Induced e.m.f (electromotive force):L= inductance in Henrydi/dt = rate of change of current.
FACTORS THAT AFFECT INDUCTANCE OF A COIL. Number of turns in the coil Permeability of the core material. Size of core.Inductance is given by,
Permeability is the measure of the ability of a material to support the formation of a magnetic field within itself.
An inductor consist of copper wire wound around a core made up of a ferromagnetic material.
FERRO MAGNETIC MATERIAL
TYPES Fixed inductors Air core inductors Iron core inductors Ferrite core inductors Variable inductors.
FIXED INDUCTORSAIR CORE INDUCTORS Former made up of ceramic plastic or cardboard.
Air will be there inside former. It has the least inductance, since in air all magnetic lines produced by changing current do not link with every turn of coil, many of them lost in space.
HIGH FREQUENCY AIR CORE INDUCTORS
IRON – CORE INDUCTOR. Copper wire wound on hallow former Core material passes through the former it forms closed magnetic path for the magnetic flux. So, it donot leak outside of coil. Flux line iron + total flux Former paper or plastic Core silicon steel or ferromagnetic material in the form of sheets. Laminated Sheets to reduce hysteresis and eddy current losses.
Iron – core inductors called choke Useful at low frequencies. Value few henries. Applications: Filter circuit in power supplies. Chokes in fluorescent tubes
Eddy current electric currents induced in conductors when exposed to a changing magnetic field. Disadvantages: enormous increase in hysteresis and eddy current loss Cannot be used for high frequencies.
FERRITE CORE INDUCTORS ForHigh frequency applications. Core ferrite an insulator having high permeability. Ferrite hard, dense ceramics made of ferric oxide +metal oxides
Ferrite core solid and not in laminated sheets Because of their high resistivity. Value few μH to few mH.
APPLICATIONS R.f chokes for supply decoupling purposes. Switching regulated type d.c power supplies Various types of filters in communication equipment.