Electrical Principals Chapter 4

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Nov 2, 2013 (3 years and 11 months ago)

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Electrical Principals

Chapter 4

Conductors, Conductance, Insulators,
Resistivity, Temperature on Conductors,
Resistors, Resistor Types, Resistor Values,
Variable Resistors, Capacitors, Diodes,
Transistors, Digital Logic Gates,

Conductors,

Temperature
Effects on Conductors, and
Insulators

Conductors


A
Conductor

is a material that has
very little resistance and permits
electrons to move through it easily.


Conductors

include wire, cable, and
cord.


Electrical circuits and components are
connected using
Conductors.

Conductors


Conductor

material include copper,
aluminum, copper
-
clad aluminum, steel, and
bronze.


Copper and Aluminum are the most
commonly used materials.


Copper is most common.


Copper is preferred because it has a lower
resistance than aluminum for any given wire
size.

Conductors


Conductance
is the measure of how
good a conductor is at carrying
current.


Conductance

is inversely proportional
to resistance.


A good
Conductor

has a high
Conductance

value and a very small
resistance to current flow.

Conductors


Conductors
are not meant to offer
any resistance or opposition to current
flow.


Conductance

is the measure of how
good a
Conductor

is, and even the
best
Conductors

have some value of
resistance.


We can calculate a

Conductor’s
resistance with the formula
R=V/I

Temperature Effects on
Conductors


When heat is applied to a
Conductor
,
the atoms within the
Conductor

convert this thermal energy into
mechanical energy or movement.


These random moving atoms cause
collisions between the directed
electrons (current flow) and the
adjacent atoms, resulting in an
opposition to current flow (resistance
).

Temperature Effects on
Conductors


This means the greater the heat
applied to the conductor (more current
flowing), the greater the atom
movement, causing more collisions of
atoms to occur and consequently,
greater conductor resistance.


More current more heat. More heat
more resistance.

Insulators


Insulators

is any material that offers
high resistance or opposition to current
flow.


Remember
Conductors

permit the
easy flow of current.


Insulators

can, with sufficient
pressure or voltage applied across
them, “break down” and conduct
current.

Resistors, Resistance,

and

Resistivity

Resistivity


Resistivity

is the resistance (in Ohms)
that a certain length of conductive
material (in feet) will offer to the flow of
current.

Resistors, Resistance, and
Resistivity


Electrical Resistance

is opposition to
the flow of electrons through any
material.


A
Resistor

is a device that limits the
current flowing in an electronic circuit.


Resistors

are classified by their
resistance value (in
Ώ
) and their power
dissipation (in Watts).

Resistors, Resistance, and
Resistivity


Resistors

are used for dividing
voltage, reducing voltage, developing
heat, and limiting current.


Resistors

may be fixed, variable or
tapped.


A
Fixed Resistor

is a
Resistor

with a
set value, such as 100
Ώ
.

Resistors, Resistance, and
Resistivity


A
Variable

(adjustable)

Resistor

is a
resistor with a set range of values,
such as 0
Ώ

to 1000
Ώ
.


A
Tapped Resistor

is a resistor that
contains fixed tap points of different
resistances.


A
Thermistor

is a device that changes
resistance with a change in
temperature.
Thermistors

are
semiconductor devices.

Resistors, Resistance, and
Resistivity


There are two types of
Thermistors


positive temperature coefficient (
PTC
) and
the negative temperature coefficient (
NTC
).


A
PTC Thermistor

has an increasing
resistance value with an increase in
temperature.


A
NTC Thermistor

has a decreasing
resistance value with an increasing in
temperature. The
NTC Thermistor

is the
most common type.



Resistors, Resistance, and
Resistivity

Capacitance, Capacitors,


Diodes and Transistors


Capacitance, Capacitors,
and Diodes


Capacitance

is the ability to store
energy in the form of an electrical
charge.


Capacitance

is the property of an
electric device that permits the storage
of electrically separated charges when
potential differences exist between the
conductors.

Capacitance, Capacitors,
and Diodes


A
Capacitor

is an electric device
designed to store electrical energy by
means of an electrostatic field.


Capacitors

are used as filters in AC
circuits to block DC voltages in
electronic circuits, and to improve
torque in motors.

Capacitance, Capacitors,
and Diodes


Capacitors

include fixed, variable, and
electrolytic polarized.


Once
Capacitors

are discharged, the
must be recharged.


Tolerance of some
Capacitors

is
indicated by a letter code following the
number.

Capacitance, Capacitors,
and Diodes


A
Diode

is a semiconductor device
that offers very high opposition to
current flow in one direction and very
low opposition to current flow in in the
opposite direction.


Diodes

are also know as
Rectifiers

because they change AC into
pulsating DC.

Capacitance, Capacitors,
and Diodes


Diodes

are rated according to their
type, voltage, and current capacity.


The most common types of diodes
include zener, tunnel,
photoconductive, and light
-
emitting
diodes (
LED
).


Diodes

are a available in current
ranges of a few milliamps to over
1000A.

Capacitance, Capacitors,
and Diodes


A
Zener Diode

is a silicon PN junction that
differs from a standard diode in that it
operates in the reverse breakdown region.


A
Zener Diode
operates as a voltage
regulator in an electronic circuit.


Zener Diodes

allow varying amounts of
reverse current flow through them and
continue to maintain a relatively constant
voltage drop when reverse biased.


Capacitance, Capacitors,
and Diodes


A
Tunnel Diode

is a diode designed so that
the current flowing through the diode
decreases with an increase in applied
voltage for a specific range of forward
voltage.


Tunnel Diodes

operate as an amplifier or
oscillator in an electronic circuit.


Tunnel Diodes

exhibit negative resistance
when operated within a specific range of
forward voltage.


Tunnel Diodes

are used in logic circuits
and for level sensing.

Capacitance, Capacitors,
and Diodes


A
Photoconductive Diode

is a diode
that conducts current when energized
by light.


Photoconductive Diodes

decrease
resistance as light increases.


The
Diode

is made of photosensitive
material that decreases in resistance
with an increase in light.

Capacitance, Capacitors,
and Diodes


A
Light Emitting Diode

(
LED
) is a
Diode

that emits light when forward
current is applied.


In an
LED

is produced when current is
passed through the diode.


LEDs

are commonly used as visual
indicators because they have a very
long life.

Capacitance, Capacitors,
and Diodes

Transistors


A
Transistor

is a three
-
terminal device that
controls current through the device
depending on the amount of voltage applied
to the base.


Transistors

are made of semiconductor
material.


Transistors

are used to start and stop
(switch) current flow or to increase (amplify)
current flow in DC circuits.

Transistors


Transistors

can be
NPN

or
PNP
,
Unijunction
, and
Junction Field
-
Effect Transistors (JFET)
, and
Phototransistors
.


An
NPN Transistor

is a transistor that
is formed by sandwiching a thin layer
of P
-
type material between two layers
of N
-
type material.

Transistors


An
PNP Transistor

is a transistor that is
formed by sandwiching a thin layer of N
-
type material between two layers of P
-
type
material.


NPN

and
PNP

transistors function as a
switch. They start, stop, or increase the
flow of current in a DC circuit.


Transistors

also function as amplifiers in
allowing a very small current to control a
much larger current.


Transistors


A
Unijunction Transistor (UJT)

is a
transistor consisting of N
-
type material with
a region of P
-
type material doped within the
N
-
type material.


A
UJT

is used in timer circuits.


A
Junction Field
-
Effect Transistor (JFET)

is a device in which output current is
controlled by the voltage on the input.


Transistors


A
Phototransistor

is a transistor that
controls the amount of current flowing
through the emitter/base junction based on
the amount of light.


Phototransistors

include
NPN

and
PNP

transistors.


There is an increase of current flow with an
increase in light. A
Phototransistor

is a
combination of a
Photodiode

and a
Transistor.

Transistors

Digital Logic Gates

Digital Logic Gates


A
Digital Logic Gate

is a circuit that
performs a special logic operation such as
AND, OR, NOT, NOR, NAND,

and
exclusive
OR
.


Digital Logic Gates

are used in most
electronic devices.


Digital circuits operation on binary signals.
Binary signals have two states


the signal
is high (1) or low (0) … on (1) or off (0).

Digital Logic Gates

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