CHAPTER 6

INDUCTORS

& INDUCTANCE

End of the lessons, students

should be able to ;

• Understand inductors and

inductance

• types of inductors

• Describe the construction of an

inductor.

• Understand inductance

equivalent circuits for series

and parallel connections

INTRODUCTION • GO TO INDUCTOR VIDEO

4

Inductors

An Inductor are passive components that stores energy in the form of the magnetic field.

What is an Inductor?

A coil of wire that can

carry current

Energy is stored in the inductor

Current produces a magnetic field

Flux

i Current

Basic Inductor

Electromagnetic Field - DC

• In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. • To add inductance to a circuit, electronic components called inductors are used, typically consisting of coils of wire to concentrate the magnetic field and to collect the induced voltage.

Inductance

•The unit : henry (H), which is defined as the production of one volt of counter-emf in a coil when current has a change of one ampere per second. • The symbol : L • Inductance can be increased by looping the conductor into a coil which creates a larger magnetic field.

FIXED INDUCTOR

An inductor whose coils are wound in such a manner that the turns remain fixed in position with respect to each other.

TYPES OF INDUCTORS :

SYMBOL :

a) Air core inductors Inductance value is micro henry or less and usually used in

high frequency. For example, this inductor used as radio

frequency choke to prevent the current radio frequency

(high frequency) of a particular route in the circuit.

b) Iron core-coils The iron core is laminated iron core coated with a thin

insulator. Inductance value of the iron core is a few

millimeter to several henry. It is used as a low-frequency

filter in the voltage supply circuit. It is also used as a choke in the circuit of “lampu pendaflour”

(c)Powder iron core inductors and ferrite core inductors

Powder iron core is produced with the appearance of

iron powder covered by insulation. Ferrite core is made

of non-conductive magnetic material. By using powder

iron core or ferrite iron core, the inductance will be

higher and the size can be reduced.

They have three forms, namely a solenoid, toroid and

pot core. Solenoid type 1micro henry inductance value

or less while the pot core and toroid have the

inductance values between a few to a few milli

microhenry.

Normally used in radio tuning circuits.

VARIABLE INDUCTOR

- A coil whose effective inductance can be changed. - can be constructed by making one of the terminals of the device a sliding spring contact that can move along the surface of the coil, increasing or decreasing the number of turns of the coil included in the circuit. -An alternative construction method is to use a moveable magnetic core, which can be slid in or out of the coil. - Moving the core farther into the coil increases the permeability, increasing the inductance.

- Many inductors used in radio applications (usually less than100 MHz) use adjustable cores in order to tune such inductors to their desired value, since manufacturing processes have certain tolerances (inaccuracy). - Sometimes such cores for frequencies above 100 MHz are made from highly conductive non- magnetic material such as aluminum. - They decrease the inductance because the magnetic field must bypass them.

L = N2µA / l L=inductance, N= number of turns

l = core length in meters (m), µ= permeability (H/m)

Basic Construction -It is basically constructed using a copper wire wrapped around a core make of ferromagnetic material or just around the air. - Using ferromagnetic material help to confine the magnetic flux within the coil and hence increasing the inductance of the coil. -The copper wire must have good insulation to prevent shorting of the wires to one another. - In some circuitry, there is a need to change or tune the value of the inductance hence an adjustable core type is used. - An inductor is usually constructed as a coil of conducting material, typically copper wire, wrapped around a core either of air or of ferrous material. - Core materials with a higher permeability than air confine the magnetic field closely to the inductor, thereby increasing the inductance.

A typical toroidal coil that is wrapped around an iron core

TYPES OF INDUCTANCE

EQUIVALENT CIRCUIT CONNECTION

1.SERIES CONNECTION

2.PARALLEL CONNECTION

3.SERIES-PARALLEL CONNECTION

Solution..

Series-parallel inductances