Transcript Transistors

Transistors
After the World War 2 (1948) the
Transistor was invented in the Bell
Laboratories in the USA (by Bardeen,
Brattain and Shockley)
The First Transistor
The First Transistor
Colour
Picture
Hearing Aids were the first commercial
application of the new solid state invention
(1952)
The First Transistorized Hearing Aid
No I don’t Know how it was used
In 1954 the first transistor radio called
the “Regency TR-1” was produced with
the help from Texas Instruments
It sold for about $49 which would be equal
to over $300 dollars today
The First Transistor Radio
Your Grandparents probably had one to listen to the
new music that was just starting called
Rock and Roll
So why are transistors so important.
• They can be thought of as an electronic
switch
• The development of the transistor was the
key component to the development of the
modern computer.
• Without the development of the transistor
your home computer would look like..
No there wasn’t a smaller “Laptop version” available
What is a transistor?
• In basic terms a transistor is a semi-
conductor device made up of three
separate parts
• These parts are called the Emitter, the
Base and the Collector
These parts are put together like a sandwich
with the Base being between the Emitter
and the Collector
Emitter
Base
Collector
Origin of the names
• the Emitter 'emits' the electrons which
pass through the device
• the Collector 'collects' them again once
they've passed through the Base
• ...and the Base?...
Transistors essentially consist of a pair of PN Junction
Diodes that are joined back-to-back. This forms a sort
of a sandwich where one kind of semiconductor is
placed in between two others. There are therefore two
kinds of sandwich, the NPN and PNP varieties.
Schematic Symbols
collector
collector
base
base
emitter
NPN transistor
emitter
PNP transistor
Notice the difference in the arrow head on the Emitter it always points
towards the part (either the Base or the Emitter) that must be more
negative for the transistor to turn on.
Transistors have 2 basic uses today
• To amplify an input signal
• To act as an electronic switch
• When a transistor is used as a switch it uses the
•
•
base voltage to turn the transistor on or off
By doing this a transistor can use a very low
current and voltage to control a much higher
current
When a transistor is turned on essentially the
electrons flow straight from the Emitter to the
Collector
In the next few slides we will look at how an
NPN transistor is used to simulate a switch
Transistor as a Switch
Transistor
Switch
• Transistors can either
conduct or not conduct current.
• ie, transistors can either be on or off.
How Transistors Work
Collector
• Switching is
controlled by
the voltage
between the
Base and the
Emitter.
Base
Emitter
• When VBE < 0.7V the transistor switches off and
no current flows between the Collector and the Emitter.
• When VBE ≥ 0.7V the transistor switches on and
current flows between the Collector and the Emitter.
• When a Transistor is “turned off” . Which in the
•
case of the NPN transistor is when the difference
between the base voltage and the Emitter
voltage is less than 0.7 Volts there is no
connection between the Emitter and Collector
(open circuit)
If you used a meter to measure the voltage
difference between the Emitter and the Collector
you would read all the voltage availible
• When a Transistor is “turned on” . Which in the
•
case of the NPN transistor is when the difference
between the Base voltage and the Emitter
voltage is more than 0.7 Volts there is a
connection between the Emitter and Collector
(closed circuit)
If you used an meter to measure the voltage
difference between the Emitter and the Collector
you would read approximiately 0.2 Volts
Base Thickness
The thickness of the Base has to be just right.
– Too thin, and the Base would essentially vanish. The
Emitter and Collector would then form a continuous
piece of semiconductor, so current would flow
between them whatever the base potential.
– Too thick, and electrons entering the Base from the
Emitter wouldn't notice the Collector as it would be
too far away. So then, the current would all be
between the Emitter and the Base, and there'd be no
Emitter-Collector current.
• So what is the correct thickness of the
base. This depends on the transistor and
the amount of current it controls but on
most transistors the base is only a micron
to an atom in thickness.
Why does it have to be so thin you ask
Pentium D processors
376 million transistors