Handbook for Sound Engineers

Resistors, Capacitors, and Inductors 265

levels of magnetic flux. This allows a high level of dc to
flow through the core before saturation.
Powdered iron cores are close to 100% iron whose
particles are insulated and mixed with a binder such as
epoxy or phenolic. They are pressed into a final shape
and cured by baking.

10.3.1.13 Radial Inductor

A radial inductor is constructed on a core with leads on
the same side, Fig. 10-24C. This allows for easy
mounting on circuit boards, etc.

10.3.1.14 Shielded Inductor

A shielded inductor has its core designed to contain the
majority of the magnetic field. Some are self shielding
such as toroids, e-cores, and pot cores. Bobbin and slug
cores require a magnetic sleeve for shielding.

10.3.1.15 Slug Core

Slug cores have the shape of a cylindrical rod and come
with or without leads, Fig.10-24D. They have higher
flux density characteristics than other core shapes as
most of the magnetic energy is stored in the air around
the core.

10.3.1.16 Tape Wound Core

Tape wound cores are made by rolling insulated and
precisely controlled thickness strips of alloy iron into a
toroidal shape. The finished cores have an outside
coating for protection.

Tape wound cores are capable of storing high
amounts of energy and contain a high permeability.

10.3.1.17 Toroidal Inductor

Toroidals are constructed by placing the winding on a
donut-shaped core, Fig. 10-24E. Toroidal cores may be
ferrite, powdered iron, tape wound, or alloy and high
flux.

Toroidals are self shielding andhave efficient energy
transfer, high coupling between windings, and early
saturation.

10.3.2 Impedance Characteristics

Impedance. The impedance or inductive reactance

(XL) of an inductor to an ac signal is found with the

equation

(10-25)

where,

f is the frequency in hertz,

L is the inductance in henrys.

The inductance of a coil is only slightly affected by

the type of wire used for its construction. The Q of the

coil will be governed by the ohmic resistance of the

wire. Coils wound with silver or gold wire have the

highest Q for a given design.

To increase the inductance, inductors can be

connected in series. The total inductance will always be

greater than the largest inductor

(10-26)

To reduce the total inductance, place the inductors in

parallel. The total inductance will always be less than

the value of the lowest inductor

(10-27)

To determine the impedance of circuits with resis-

tance, capacitance, and inductance, see Section 10.4.

Mutual Inductance. Mutual inductance is the property

that exists between two conductors that are carrying

current when the magnetic lines of force from one

conductor link with the magnetic lines of force of the

other. The mutual inductance of two coils with fields

interacting can be determined by

(10-28)

where,

M is the mutual inductance of LA and LB in henrys,

LA is the total inductance of coils L 1 and L 2 with fields

aiding in henrys,

LB is the total inductance of coils L 1 and L 2 with fields

opposing in henrys.

The coupled inductance can be determined by the

following equations.

In parallel with fields aiding

XL= 2 SfL

LT=L 1 ++L 2 } Ln

LT^1

1

L 1

-----

1

L 2

----- }^1

Ln

++-----

=---------------------------------------

M

LA–LB

4

=------------------