Tài liệu Malvino-EP-01-Introduction pdf

An ideal voltage source maintains a constant output voltage, regardless of the value of R,.. The ideal model can be called the first approximation... This model is called the the second

MALVINO Electronic

PRINCIPLES

SIXTH EDITIC

Introduction

Three kinds of formulas

The definition: Invented for a new concept

{does not require verification } The law: Summarizes a relationship that exists in nature

Q,Q

The derivation: Obtained by manipulating other

formulas using mathematics

“Sa 9 = cv

An ideal voltage source maintains a constant

output voltage, regardless of the value of R,

The ideal model can be called

the first approximation

A real voltage source has

a series resistance

This model is called the the second approximation

When R, is equal to or greater than 100 times Rg, a real voltage source is stiff and the first approximation can be used.

An ideal current source maintains a constant

output current, regardless of the value of R,

1A (t) Ry lạ, = 1 Ampere

The ideal model can be called

the first approximation

A real current source has

a shunt resistance

1A (t) Rg R, Iz, < 1 Ampere

This model is called the the second approximation

When R, is equal to or greater than 100 times R,, a real current source is stiff and the first approximation can be used.

Thevenin’s theorem can be used to replace any linear circuit with an equivalent voltage source

called V,,, and an equivalent resistance called Ry

Calculate or measure Ràn.

When working with actual circuits, please remember this guideline:

The input impedance of

a voltmeter should be at least 100 times

ereater than the Thevenin resistance to

avoid loading error

DMMs are usually not a problem since they typically have an impedance of 10 MQ

The original

circuit

The Thevenin

equivalent circuit

6kO 4 kO

——€VNXN"

6 kQ (Ryy) -— 24V(V„,)

Norton’s theorem can be used to replace any linear circuit with an equivalent current source

called I, and an equivalent resistance called Ry

Ry 1s the same as Ry.

The original

circuit

The Norton

equivalent circuit

— 72V 3 kQ

Ry

—WW

6 k© (Rm)

equivalent circuit ——— 24V (Vm)

V nh

Ry — Rory In = R,

The Norton

dual Ct 4m (Iy) 6 kQ (Ry)

Troubleshooting

¢ A solder bridge between two lines

effectively shorts them together

¢ A cold solder joint is effectively an open circuit

e An intermittent trouble is one that

appears and disappears (could be a cold solder joint or a loose connection).

An open device

¢ The current through It Is zero

¢ The voltage across it is unknown

e V =zero x infinity {indeterminate}

A shorted device

¢ The voltage across it Is zero

e¢ The current through it is unknown

¢ I[=0/0 {indeterminate}

A troubleshooting example:

Do the two 10 Q resistors form

a stiff voltage divider?

100 kQ

Why?

A troubleshooting example:

What are the expected

voltages in this circuit?

100 kQ

A troubleshooting example:

What are some causes for

this voltage being too high?

100kQ V

A troubleshooting example:

What are some causes for

this voltage being too low?

100kQ V