Download Introduction to Inductance and Inductors

Introduction to
Inductance and Inductors
Online Resource for ETCH 213
Faculty: B. Allen
Self-inductance
Self-Inductance – The property that causes a counterelectromotive force to be produced in a conductor
when a magnetic field expands or collapses with a
change in current.
Counter Electromotive Force (emf) – The voltage
generated in an inductor due to alternating or pulsating
current. It is always of opposite polarity to that of the
applied voltage.
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Inductance
Inductance - The property of a circuit or component
to oppose any change in current as the magnetic field
produced by the change in current causes an induced
countercurrent to oppose the original change.
Henry – The unit of inductance.
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Inductor
Inductor – A coil of conductor used to introduce
inductance into a circuit.
Factors determining Inductance:
1. Number of turns
2. Area of the coil
3. Length of the coil
4. Core material used within the coil
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Inductance is proportional to the number of turns.
Inductance is proportional to the area of the coil.
Inductance is inversely proportional to the length of
the coil.
Inductance in proportional to the permeability of the
core.
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N Aµ
L=
l
2
L = Inductance in Henrys
N = Number of turns
A = Cross-sectional area of the coil in square meters
µ = Permeability of the core material
l = Length of the coil in meters
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Inductors in series
LT = L1 + L2 + L3 + …
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Inductors in parallel
LT =
1
1 1
1
+ + + ...
L1 L2 L3
For two inductors in parallel:
L1 × L2
LT =
L1 + L2
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Inductors in parallel
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Types of inductors
Fixed-Value Inductors
Air Core
Iron Core
Ferrite Core
Variable-Value Inductors
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Fixed-value inductors
Fixed-Value Inductor – An inductor whose value is fixed.
Air-Core Inductor – An inductor that has no metal core.
Iron-Core Inductor or Choke – An inductor used to impede the
flow of alternating or pulsating current.
Ferrous – Composed of or containing iron. A ferrous metal
exhibits magnetic characteristics as opposed to nonferrous
metals.
Ferrite – A powered, compressed and sintered magnetic
material having high resistivity. The high resistance makes
eddy-current losses low at high frequencies.
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Variable-value inductor
An inductor whose value can be varied
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Inductive time constant
L
τ=
R
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DC current fall
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AC current rise and fall
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Inductive reactance (XL)
Inductive Reactance (XL) – Measured in ohms, it is
the opposition to alternating or pulsating current flow
without the dissipation of energy.
XL = 2 π f L
f = frequency in hertz
L = inductance in henrys
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Voltage in series RL circuits
VR = I × R
VL = I × XL
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Impedance in series RL circuits
Z = V/I
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Phase shift in series RL circuits
XL
θ = arctan
R
VL
θ = arctan
VR
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Power in series RL circuits
Purely inductive circuit
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Quality Factor
Quality Factor – The quality factor of an inductor or a
capacitor is the ratio of a component’s reactance (energy
stored) to its effective series resistance (energy dissipated).
Quality
Factor
(Q ) =
Energy
Energy
XL
Q=
R
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Stored
Dissipated
Power in an RL circuit
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Power Factor
PF =
True
(PR )
Power (PA )
Power
Apparent
or
PF = R/Z
or
PF = cos
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Current in parallel RL circuits
VS
IR =
R
VS
IL =
XL
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Phase angle in parallel RL
circuit
IL
θ = arctan
IR
θ = arctan
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R
XL
Impedance in a parallel RL
circuit
VS
Z=
IT
Z=
R× XL
R +X
2
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2
L
Applications of inductors
RL Filter – A selective
circuit of resistors and
inductors that offers little
or no opposition to certain
frequencies while blocking
or attenuating other
frequencies.
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RL Integrator – An RL circuit with an output proportional to
the integral of the input signal.
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RL Differentiator
– An RL circuit
whose output
voltage is
proportional to
the rate of change
of the input
voltage.
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End of
Inductance and Inductors
Online Resource for ETCH 213
Faculty: B. Allen