Transistors - Choquettetech.org

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2 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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Transistors



The Transistor was invented in
1948


and


The New York Herald Tribune announced the
invention of the transistor as the …

“Electronic device that will change our very life's
existence".


The reason for this life changing label is because
these small components are only controlled by
other small components. This is known as
micro
-
electronics.


Three scientist John Bardeen, Walter
Brattain and William Shockly at Bell
Laboratories in New York City worked with
materials such as silicon or germanium to
produce crystalline materials (aka chips)
that would function as
semiconductors.



Semiconductors are chips that, in their natural
state, are solidly insulators, but when salted with
impurities such as boron or phosphorus they
become excellent conductors.


By using semiconductor chips, scientists could
duplicate electronics processes that the vacuum
tubes were doing yet without
warm
-
up

time, less
cost
, less,
power
,
faster
,
smaller
, longer
life
, and
less
weight
.


Also a Semiconductive transistor is able to
work as anyone of three fundamental
processes. A
switch
, it could
amplify
current, and able to convert DC and
AC
.


The first Transistor emerged on the market
as a
bipolar

transistor. It worked with the
idea of junction voids and bridges. Lets
look at this concept.


Remember
, that a Semiconductors can be
formed to have a negative charge and
allow current to flow by electrons or can be
formed to have a positive charge and
allow current to flow by solid
-
state holes.
These are known as
N
-
type

or
P
-
type

materials.


Transistors are basically a configuration of
two solid
-
state diodes back to back and
combines
three

layers of N
-
type and P
-
Type materials alternately so they form
both types of transistors;



negative, positive, negative (
NPN
)


positive, negative, positive. (
PNP
)


NPN and PNP transistor configurations
work just the same except that they allow
current to flow in
opposite

directions.


The term that defines the polarity
connection of the transistor is
bias
. If it is
connected in forward
-
bias then the
component will function correctly, if in
reverse
-
bias the transistor will restrict
current flow.


In order to define the bias of a transistor
you must know the names of the leads.
There are three:

base, emitter
, and
collector


When a N
-
type chip and a P
-
type chip
come in contact with each other a
junction

is created and depending on the bias of
the transistor the junction can either be a
bridge

or a
void

.



The base is a very thin center layer (only about
.001

inches thick) of material and is the
saturation

region were electrons or holes are fed
into the transistor to allow it to
pass
current.


The emitter is the
sending

lead that (if in
forward
-
bias) will receive current from the
battery and send it through the base region then
onto the
receiving

lead, the collector.


Only
5%

of the current flowing in a
transistor is through E/B junction, the other
95%

flows through the E/C junction. So
when a slight change occurs in the E/B a
larger change occurs in the EC.



If the transistor is in reverse
-
bias a void is
induced around one of the junctions and
cause current to slow or stop.


The process of controlling a large current
by a small current is called
amplification.


Transistors are packaged in several styles
of casings and it is necessary to always
verify

which lead is which because they
are not always in the same location on all
casing styles.


And finally, the
rating

of a transistor tells
us how many times the E/C current will be
higher than the
E/B

current.