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Basic Electronic ==>

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JFET The Junction Field Effect Transistor

Vacuum Tubes

Permanent Magnet Motor Control

The Schottky Diode

Zener Diodes

Optical Components

Regulators

Multimeters

Capacitor Colour Code

Introduction

Transformers Equivalent Circuits

Nonideal Transformers

Transformer Operation

Inductance And Magnetic Energy

Magnetic Circuits

Optocouplers

7 SEGMENT DISPLAY

DIAC

TRIAC

THYRISTOR

LEDS

Semiconductor DIODES

Types Of Capacitors

CAPACITORS

INDUCTORS

Resistor Color Code

THERMISTOR

Types Of Resistors

Variable Resistors

Metal Film Resistors

Carbon Film Resistors

RESISTORS

Switching With Transistor

How Does Transistor Work?

Transistors - BJT Introduction

Transistor Specifications

36 topics total

Vacuum Tubes

Permanent Magnet Motor Control

The Schottky Diode

Zener Diodes

Optical Components

Regulators

Multimeters

Capacitor Colour Code

Introduction

Transformers Equivalent Circuits

Nonideal Transformers

Transformer Operation

Inductance And Magnetic Energy

Magnetic Circuits

Optocouplers

7 SEGMENT DISPLAY

DIAC

TRIAC

THYRISTOR

LEDS

Semiconductor DIODES

Types Of Capacitors

CAPACITORS

INDUCTORS

Resistor Color Code

THERMISTOR

Types Of Resistors

Variable Resistors

Metal Film Resistors

Carbon Film Resistors

RESISTORS

Switching With Transistor

How Does Transistor Work?

Transistors - BJT Introduction

Transistor Specifications

36 topics total

Transformers

MAGNETIC CIRCUITS

A *magnetic circuit *is a path for magnetic flux, just as an electric circuit provides a path for the flow of electric current. Transformers, electric machines, and numerous other electromechanical devices utilize magnetic circuits. *Magnetic induction *or *magnetic flux density, B, *is defined by the force equation

*F *= *B l *I * *(Formula 1)

where *F *(N) is the force experienced by a straight conductor oflength *t(m) *which carries a current *i *(A) and is oriented at right angles to a uniform magnetic field of flux density *B *(T). In other words, if a conductor is 1 meter long, carries 1 ampere of current, and experiences 1 newton force when located at right angles to parallel magnetic flux lines, then the magnetic flux density is 1 tesla. Actually, the magnetic induction is a vectar, B, of magnitude *B *and tangential to the flux lines. If B is uniform over a surface of area *A *and is everywhere perpendicular to the surface, *magnetic flux, Φ, *is determined by

* *(Formula2)

The unit of magnetic flux is the weber (Wb), and (2) shows that

1 T = 1 Wb/m2.

The source of magnetic flux is either a permanent magnet or an electric current. To measure the

effectiveness of electric current in producing a magnetic field (or flux), the concept of magnetomotive force (mmf), F, defined as

*F *= *NI** *(Formula 3)

is introduced where *I *is the current flowing in an *N-turn *coil. The unit of *F *is the *ampere turn *(At). Schematically, a magnetic circuit with an mmf and magnetic flux is shown in below.

The core material of a magnetic circuit (constituting a transformer or an electric machine) is generally ferromagnetic, and the variation of *B *with *H (magnetic field intensity *measured in units of A/m or At/m) is depicted by *asaturation curve, *as shown in Fig. 2. For region II, where the slope of the curve is nearly constant, we may write

*B *= μ*H ** *(Formula 4)

where μ, (H/m) is defined as the *permeability *of the material. For free space (or air), μ = μo = 4 л x 10^{-7} H/m.

Figure 2

Magnetic circuits obey the analog of Ohm´s law; the complete analogy between magnetic and dc resistive circuits is displayed in Table 13-1 ,where *t *is the length and *A *is the cross-sectional area of the path for the current in the electric circuit, or for the flux in the magnetic circuit. By the analogy, the laws of resistances in series or parallel also hold for reluctances.

DC Resistive Circuit | Magnetic Circuit |

current, I |
flux,Φ |

voltage, V |
mmf, F |

conductivity, σ |
permeability,μ |

Ohm´s law, I = V / R |
Φ = F / R |

resistance, R =l / σ A |
reluctance, R = l /μ A |

conductance, G = 1/ R |
permeance, P = 1 / R |

Table 1 |

The *dijferences *between a dc resistive circuit and a magnetic circuit are:

(1) there is an*I2R-loss *in a resistance but no *Φ*2R-loss in a reluctance;

(2) magnetic fluxes take*leakage *paths, as *Φ**l*in Fig. 2, whereas electric currents (flowing through resistances) do not;

(3) Magnetic circuits are non-linear through the*B-H *characteristic of Fig. 2;

(4) in magnetic circuits with air gaps we encounter*fringing *(Fig. 2) of flux lines, but we do not have fringing of currents in electric circuits. Fringing increases with the length of the air gap, and increases the effective cross-sectional area of the air gap.

(1) there is an

(2) magnetic fluxes take

(3) Magnetic circuits are non-linear through the

(4) in magnetic circuits with air gaps we encounter

Keywords : Magnetic, Induction, Transformer, Transformation, Electrical, Electronic

16 Mar 2006 Thr

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