Download tcom 308-3-Inductors

Inductors
Inductance
• Electrons in motion create electromagnetic
fields
– Recall from previous section that electrons in
motion also create an electrostatic field
• The electromagnetic field can be intensified
by making a loop in the wire
• A device which creates an electromagnetic
field is called an inductor
Inductors
Schematic symbol for inductor or coil
Inductance
• The unit of measure of inductance is henry
• The inductor is an electromagnet
• One use of the inductor is in relays to operate
a switch
• Another use is in the construction of electric
motors
Relays
Contacts
Relays
12 volts
760 volts
M
Relays
M
Relays
M
Inductors
Inductors
Inductors
• Three factors affecting inductance
– Nature of the coil
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•
•
•
Size
Diameter of conductor
Number of turns
Length
– Current flow
– Presence of materials within the magnetic field
Variable Inductor
Inductors
• When current is turned off from
electromagnet, the electromagnetic field
collapses back to the coil
• There is a charge or current present on the
inductor
• Electromagnetic energy is stored in inductors
• Inductors are used to convert AC to DC
Inductors
Inductor
Capacitor
10 volts
0 volts
“on”
“on”
“off”
Time
“off”
Inductors
• Energy is expended in forming
electromagnetic field
• Inductors resist current flow – electrons resist
flow
• Impedance is reluctance in a coil
• Three factors affecting inductance also affect
impedance
Transformers
• Transformers are constructed from two
inductors or coils in close proximity to one
another
• Just like capacitors, current can be induced to
flow in the secondary coil if enough current
flows through the primary
• Transformers are used to increase or decrease
current flow and/or voltage
Transformers
Primary
Secondary
Transformers
• Step up transformers have more turns in the
secondary coil and increase output
• Step down transformers have fewer turns in
the secondary and decrease output
• Isolating transformers have same number of
turns in both coils and neither decrease nor
increase output – but isolate two segments of
a circuit
Transformers