PPT: Magnetically Coupled Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE) PDF Download

 Page 1


1
Magnetically Coupled 
Circuits
Page 2


1
Magnetically Coupled 
Circuits
Magnetically Coupled Circuits
INTRODUCTION
• The circuits we have considered may be regarded as 
conductively coupled, because one loop affects the 
neighboring loop through current conduction. When two 
loops with or without contacts between them affect each 
other through the magnetic field generated by one of them, 
they are said to be magnetically coupled.
• The transformer is an electrical device designed on the basis 
of the concept of magnetic coupling. It uses magnetically 
coupled coils to transfer energy from one circuit to another. 
• Transformers are used in power systems for 
• stepping up or stepping down ac voltages or currents. 
• They are used in electronic circuits such as radio and 
television receivers for such purposes as impedance 
matching, isolating one part of a circuit from another
2
? 
Page 3


1
Magnetically Coupled 
Circuits
Magnetically Coupled Circuits
INTRODUCTION
• The circuits we have considered may be regarded as 
conductively coupled, because one loop affects the 
neighboring loop through current conduction. When two 
loops with or without contacts between them affect each 
other through the magnetic field generated by one of them, 
they are said to be magnetically coupled.
• The transformer is an electrical device designed on the basis 
of the concept of magnetic coupling. It uses magnetically 
coupled coils to transfer energy from one circuit to another. 
• Transformers are used in power systems for 
• stepping up or stepping down ac voltages or currents. 
• They are used in electronic circuits such as radio and 
television receivers for such purposes as impedance 
matching, isolating one part of a circuit from another
2
? 
INTRODUCTION
• Whenever current flows through a conductor, a magnetic field 
is generated about that conductor. In circuits, we often refer 
to the magnetic flux through a loop of wire. When a time-
varying magnetic field generated by one loop penetrates a 
second loop, a voltage is induced between the ends of the 
second wire. In order to distinguish this phenomenon from 
the “indu c tance ’ ’ we will define a new term, mutual 
inductance.
• A transformer consists of two coils of wire separated by a 
small distance, and is commonly used to convert ac voltages 
to higher or lower values depending on the application. 
• Electrical appliance that requires dc current to operate but 
plugs into an ac wall outlet makes use of a transformer to 
adjust voltage levels prior to rectification, a function typically 
performed by diodes.
3
? 
Page 4


1
Magnetically Coupled 
Circuits
Magnetically Coupled Circuits
INTRODUCTION
• The circuits we have considered may be regarded as 
conductively coupled, because one loop affects the 
neighboring loop through current conduction. When two 
loops with or without contacts between them affect each 
other through the magnetic field generated by one of them, 
they are said to be magnetically coupled.
• The transformer is an electrical device designed on the basis 
of the concept of magnetic coupling. It uses magnetically 
coupled coils to transfer energy from one circuit to another. 
• Transformers are used in power systems for 
• stepping up or stepping down ac voltages or currents. 
• They are used in electronic circuits such as radio and 
television receivers for such purposes as impedance 
matching, isolating one part of a circuit from another
2
? 
INTRODUCTION
• Whenever current flows through a conductor, a magnetic field 
is generated about that conductor. In circuits, we often refer 
to the magnetic flux through a loop of wire. When a time-
varying magnetic field generated by one loop penetrates a 
second loop, a voltage is induced between the ends of the 
second wire. In order to distinguish this phenomenon from 
the “indu c tance ’ ’ we will define a new term, mutual 
inductance.
• A transformer consists of two coils of wire separated by a 
small distance, and is commonly used to convert ac voltages 
to higher or lower values depending on the application. 
• Electrical appliance that requires dc current to operate but 
plugs into an ac wall outlet makes use of a transformer to 
adjust voltage levels prior to rectification, a function typically 
performed by diodes.
3
? 
13.1 MUTUAL INDUCTANCE
• When we defined inductance in previous course, we did so 
by specifying the relationship between the terminal voltage 
and current, 
• The physical basis for such a current-voltage characteristic 
rests upon two things:
 1. The production of a magnetic flux by a current, the 
flux being proportional to the current in linear inductors.
 2. The production of a voltage by the time-varying magnetic 
field, the voltage being proportional to the time rate of change 
of the magnetic field or the magnetic flux.
4
? 
Page 5


1
Magnetically Coupled 
Circuits
Magnetically Coupled Circuits
INTRODUCTION
• The circuits we have considered may be regarded as 
conductively coupled, because one loop affects the 
neighboring loop through current conduction. When two 
loops with or without contacts between them affect each 
other through the magnetic field generated by one of them, 
they are said to be magnetically coupled.
• The transformer is an electrical device designed on the basis 
of the concept of magnetic coupling. It uses magnetically 
coupled coils to transfer energy from one circuit to another. 
• Transformers are used in power systems for 
• stepping up or stepping down ac voltages or currents. 
• They are used in electronic circuits such as radio and 
television receivers for such purposes as impedance 
matching, isolating one part of a circuit from another
2
? 
INTRODUCTION
• Whenever current flows through a conductor, a magnetic field 
is generated about that conductor. In circuits, we often refer 
to the magnetic flux through a loop of wire. When a time-
varying magnetic field generated by one loop penetrates a 
second loop, a voltage is induced between the ends of the 
second wire. In order to distinguish this phenomenon from 
the “indu c tance ’ ’ we will define a new term, mutual 
inductance.
• A transformer consists of two coils of wire separated by a 
small distance, and is commonly used to convert ac voltages 
to higher or lower values depending on the application. 
• Electrical appliance that requires dc current to operate but 
plugs into an ac wall outlet makes use of a transformer to 
adjust voltage levels prior to rectification, a function typically 
performed by diodes.
3
? 
13.1 MUTUAL INDUCTANCE
• When we defined inductance in previous course, we did so 
by specifying the relationship between the terminal voltage 
and current, 
• The physical basis for such a current-voltage characteristic 
rests upon two things:
 1. The production of a magnetic flux by a current, the 
flux being proportional to the current in linear inductors.
 2. The production of a voltage by the time-varying magnetic 
field, the voltage being proportional to the time rate of change 
of the magnetic field or the magnetic flux.
4
? 
13.1 MUTUAL INDUCTANCE
Coefficient of Mutual Inductance
• A current flowing in one coil establishes a magnetic flux 
about that coil and also about a second coil nearby. The 
time-varying flux surrounding the second coil produces a 
voltage across the terminals of the second coil; this voltage is 
proportional to the time rate of change of the current flowing 
through the first coil. Fig a shows a simple model of two coils 
L
1
 and L
2
, sufficiently close together that the flux produced by 
a current i
1
(t) flowing through L
1
 establishes an open-circuit 
voltage v
2
(t) across the terminals of L
2
. We define the 
coefficient of mutual inductance, or simply mutual 
inductance, M
21
 , as
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