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Transformers
Linear Circuit Theory
Naehyuck Chang
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Mutual inductance Electrical isolation Mutual inductance, L
M
Coefficient of coupling, k The ratio of lines of force (flux) produced by coil 1 liking coil
2 to the total flux produced by coil 1
1
21
=k
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Mutual inductance Formula for mutual inductance
1
,
21
21
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The basic transformer Transformer
Primary winding Secondary winding Core: air, ferrite and iron
Air-core and ferrite-coretransformers High-frequency
applications
Iron-core transformers Audio frequency
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The basic transformer
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The basic transformer Turn ratio
Direction of winding
priN
Nn sec=
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Step-up/step-downtransformers
The ratio of secondaryvoltage to primary voltageis equal to the ratio of thenumber of turns in thesecondary winding to the
number of turns in theprimary winding
pripri N
N
V
Vsecsec
=
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Loading the secondarywinding
Primary power equals loadpower
Reflected load Reflected resistance
pripri I
I
I
Isecsec =
pripripri
pripripri
PIVP
IVP
IVP
==
=
=
sec
secsecsec
L
pri
pri RN
NR
2
sec
=
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Loading the secondarywinding
Transformer-coupled loadresistor of 100 Reflected resistance? Reflected resistance with
600 RL?
The primary winding is 40turns and the secondarywinding is 1000 turns.Reflected resistance?
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Matching the load and sourceresistance
Power transfer from anominal voltage source toa load
Impedance matching withreflected resistance
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Matching the load and sourceresistance
Load matched to a source by transformer coupling formaximum power transfer 75 source and 300 load An amplifier with 800 internal resistance is going to be
connected to an 8 speaker. Turn ratio?
pri
L
pri RR
NNn == sec
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As an isolation device DC isolation
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As an isolation device Power line isolation
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Nonideal transformercharacteristics
Winding resistance Flux leakage
Reduced secondaryvoltage
Winding capacitance
Power rating Apparent power rating
Efficiency %100
=
in
out
P
P
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Other types of transformers Center-tapped
transformer
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Other types of transformers Tapped transformers
Impedance matchingtransformers
Multi-winding
transformers
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Other types of transformers Voltages of the
secondary windings?
Autotransformers
One winding servesboth the primary andthe secondary
Stepping up anddown
No electricalisolation
Smaller and lighter
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DC power supply Basic
transformer-coupled DCpowersupply
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DC power supply Use of center-tapped transformer Regulated DC power supply
Design project Regulated DC power supply
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