15 Transformers

8/14/2019 15 Transformers

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Transformers

Linear Circuit Theory

Naehyuck Chang

[email protected]
mailto:[email protected]:[email protected]


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SNU [email protected]

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

15 Transformers

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