Transistors
Transistors
BJT (PNP) Electrical
Diagram
Different types and sizes
FET and BJT Transistor
Modern Electronics
First Transistor
• Purpose
▫ To amplify and switch electronic signals on or off
(high or low)
• Modern Electronics
Microprocessor
Motor Controllers
Cell Phones
Vacuum tubes
• Purpose
▫ Used as signal amplifiers and switches
▫ Advantages
 High power and frequency operation
 Operation at higher voltages
 Less vulnerable to electromagnetic pulses
▫ Disadvantages
 Very large and fragile
 Energy inefficient
 Expensive
Invention
• Evolution of electronics
▫ In need of a device that was small, robust, reliable,
energy efficient and cheap to manufacture
• 1947
▫ John Bardeen, Walter Brattain and William Schockly
invented transistor
• Transistor Effect
▫ “when electrical contacts
were applied to a crystal
of germanium, the output
power was larger than
the input.”
General Applications
P-N junction
Forward Biasing
Reverse Biasing
• P-N junction
▫ Controls current flow via external voltage
• Two P-N junctions (bipolar junction transistor,
BJT)
▫ Controls current flow and amplifies the current
flow
Transistor Categories
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Semiconductor material
Structure
Polarity
Maximum power rating
Maximum operating frequency
Application
Physical packaging
Amplification factor
Types of Transistors
• Bipolar Junction Transistor (BJT)
• Field Effect Transistors (FET)
• Power Transistors
BJT Introduction
• Bipolar Junction Transistors (BJT)
consists of three “sandwiched”
semiconductor layers
• The three layers are connected to collector
(C), emitter (E), and base (B) pins
• Current supplied to the base controls the
amount of current that flows through the
collector and emitter
BJT Schematic
• NPN
NPN
▫ BE forward bias
▫ BC reverse bias
• PNP
▫ BE reverse bias
▫ BC forward bias
PNP
BJT Characteristic Curves
Transfer Characteristic
• Characteristic curves can be drawn to show other useful parameters
of the transistor
• The slope of ICE / IBE is called the Transfer Characteristic (β)
BJT Characteristic Curves
Input Characteristic
• The Input Characteristic is the base emitter current IBE against
base emitter voltage VBE
• IBE/VBE shows the input Conductance of the transistor.
• The increase in slope of when the VBE is above 1 volt shows that the
input conductance is rising
• There is a large increase in current for a very small increase in VBE.
BJT Characteristic Curves
Output Characteristic
• collector current (IC) is nearly independent of the collector-emitter
voltage (VCE), and instead depends on the base current (IB)
IB4
IB3
IB2
IB1
BJT Operating Regions
Operating
Region
Parameters
Mode
Cut Off
VBE < Vcut-in
VCE > Vsupply
IB = IC = 0
Linear
VBE = Vcut-in
Vsat < VCE < Vsupply
IC = β*IB
Amplification
Saturated
VBE = Vcut-in,
VCE < Vsat
IB > IC,max, IC,max
>0
Switch ON
Switch OFF
BJT Applications
BJT Switch
• Offer lower cost and substantial reliability over conventional
mechanical relays.
• Transistor operates purely in a saturated or cutoff state (on/off)
• This can prove very useful for digital applications (small current
controls a larger current)
BJT Applications
BJT Amplifier
BJT Applications
BJT Amplifier
Field Effect Transistors (FET)
Chase Thompson
FET Basics
• Electric Field
• Voltage Controlled
• FET includes three distinct pieces
▫ Drain
▫ Source
▫ Gate
FET versus BJT?
Same:
• Applications: amplifier,
switch, etc.
• Relies on PNP or NPN
junctions to allow current
flow
Difference:
• Voltage vs Current Input
• Unipolar vs Bipolar
• Noise
• Higher input impedance
• Fragile and low gain bandwidth