An Overview of Transistors Lisa Ellis Joe Frankel Ryan Krauss ME 6405 Instructor: Dr. Ume Georgia In

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An Overview of TransistorsLisa EllisJoe
FrankelRyan KraussME 6405Instructor Dr.
UmeGeorgia Institute of Technology
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Outline

• Background
• Basics of Transistor operation
• Transistor Types
• Practical considerations
• Example Applications
• BJT vs. MOSFET for logic level circuits
• Summary
• References

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Background

• Invented by Bell Laboratories in 1947.
• Revolutionized the computer industry by
  eliminating the need for
• vacuum tubes
• mechanical switches
• Utilized in many products that we use every day
  such as
• TVs
• Cars
• Radios
• Microprocessors

Model of first transistor
Todays transistor
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Background Semiconductor Evolution

• 1900's Vacuum Tube invented in England, used for
  AC?DC rectifier.
• 1940's Transistor invented at Bell Labs
• Late 1950s First integrated circuit at Texas
  Instruments.
• 1960's Small Scale Integration (SSI), up to 20
  gates per chip.
• Late 1960's Medium Scale Integration (MSI),
  20-200 gates per chip.
• 1970's Large Scale Integration (LSI), 200-5000
  gates per chip.
• 1980's Very Large Scale Integration (VLSI), over
  5000 gates per chip.

Silicon (insulator)
Doped Silicon (1 P-N junction)
Transistors (multiple P-N junctions)
Microprocessors (thousands of P-N junctions)
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What is a transistor?

• 3 terminal electronic semiconductor device
• Uses small input current to get large output
  current
• A switch or a amplifier
• Main component of microprocessor

Water Tank
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Transistor composition

• Base material of transistor is silicon.
• Pure silicon is a insulator which restricts
  current flow.
• Silicon has 4 valence electrons.

Pure Silicon
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Transistor composition
Two types of dopants or impurities are added to
change conductivity
P-type (positive) Add Group III elements,
like Boron, with 3 valence electrons to create
holes for charge carriers to fill.
Hole
N-type (negative) Add Group V elements,
like Phosphorus, with 5 valence electrons to
create free charge carriers.
Free electron
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Depletion Region
P-type (positive charge)
- - - - - - - -

N-type (negative charge)
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Forward Biased Example
Supplied Current flows with hole diffusion
current
Depletion Region
P-type (positive charge)
- - - - - - - - - - - - - -

N-type (negative charge)
Holes diffuse Electrons diffuse Supplied Current
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Reverse Biased Example
Supplied Current fights against hole
current Charges can not diffuse unless supplied
current flows towards n Therefore no current
flows!
Depletion Region
P-type (positive charge)
- - - - - - - - - - - - - -

N-type (negative charge)
Holes diffuse Electrons diffuse Supplied Current
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Bipolar Junction Transistors (BJT)
Collector
Collector

• Three terminals in a BJT
• Collector (C)
• Base (B)
• Emitter (E)
• Two Types of BJTs
• NPN current flows from base to emitter
• PNP current flows from emitter to base

N
P
ib
ib
Base
P
Base
N
N
P
Emitter
Emitter
C
C
ib
ib
B
B
E
E
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2 p-n junctions form Transistor

• 1. Base-emitter junction (EBJ)
• 2. Collector-base junction (CBJ)

N
P
N
Emitter
Collector
Base
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BJT Operation as a switch
ic ß ib Where ß gain of transistor To reach
saturation ib gt ic / ß
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BJT Operation as a amplifier
As base current increases the collector current
is amplified. ic ß ib, Where ß gain of
transistor
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BJT Characteristic
BJT is not an ideal switch Small amount of
current still flows thru Vce junction when Ib is
zero.
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Types of Transistors

• Bipolar Junction Transistors (BJTs)
• Metal-Oxide-Semiconductor Field Effect
  Transistors (MOSFETs)
• Insulated Gate Bipolar Transistors (IGBTs)
• Thyristors
• Gate Turn-off Thyristors (GTOs)
• Metal-Oxide Semiconductor Controlled Thyristors
  (MCTs)

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BJTsBipolar Junction Transistors
N-P-N Type
P-N-P Type
iC
iB4
C (collector)
C
iC
iC

iB

iB
iB3
VCE
VCE
amplifier
B (base)
B
iB2


VBE
VBE
switch
-
iB1
-
-
-
E (emitter)
E
VCE
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Darlington Configurations
Need more current?
iC
Triple Darlington
iB
C
Overall Gain
B

VBE
E
-
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MOSFETsMetal Oxide Semiconductor Field Effect
Transistors
D (drain)
iD
iD
VGS 7V

6V
VDS
5V
G (gate)
4V

-
VGS
0V
VDS
-
S (source)
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IGBTsInsulated Gate Bipolar Transistors
D
iD
iD
? either ?
C

VGS
G
VDS
VDS
G

-
E
VGS
-
S
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Thyristors
Forward On-state
A (anode)
iA
Breakover w/o gate current
Breakover w/ gate current

iG
VAK
VAK
G (gate)
-
Forward blocking
Reverse blocking
K (cathode)
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Power Transistor Application3? Rectifier for DC
motor control





IDC
N
-
-
?
VAC(a)
VAC(b)
VDC
-


VAC(c)
-
DC Motor
3? Controlled Rectifier
Utility grid transmission lines
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3? Rectifier Waveforms
Delay angle
Uncontrolled (max) RMS voltage
3 AC Source Voltages, 120? apart
VDC,max
? 0?
VDC,?
Controlled RMS voltage at delay angle ?
0
? 90?
?t
? 180?
VDC(?0?) VDC,max VDC(?90?)
0 VDC(?180?) -VDC,max
Range of controlled RMS voltage with firing delay
angle 0 - 180?
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GTOsGate Turn-off Thyristors
iA
iA
A (anode)
Turn-off

Turn-on
iG
VAK
VAK
G (gate)
-
K (cathode)
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MCTsMOS-controlled thyristors
iA
Turn-off
A
A
Turn-on
G
P-Type
N-Type
G
VAK
K
K
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Switching Characteristics
Control Signal
t
Voltage / Current
OFF
OFF
ON
Turn-off
Turn-on
voff
voff
ion
t
On-state voltage drop
Power Dissipation (switching losses)
Esw (VItswitch)/2 Eon VonIonton
t
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Safe Operating Area
Outside actual SOA need protection here
Idealized switching trajectory
log(iC)
C
Ideal SOA, fast switch times
iC
iC,max

Actual SOA (high freq)
VCE
B
Actual SOA (low freq / DC)
-
E
Realistic current voltage limits while
conducting
log(vCE)
vCE,max
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Voltage Spikes
Voltage spike
i(t)

vL(t)

-
vD
iON

i(t)
?i
vON
vD
vs(t)
tts
vs(t)
t
ts
-
-
?t
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Snubber Circuits
i(t)

L
R
D
RCD Snubber circuit
vs(t)
T
C
-
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Semiconductor Limitations
Increasing frequency
Increasing power size
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Semiconductor Limitations
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Typical Applications

• Current amplification
• Audio driver applications
• Switching
• use microcontroller to turn something on or off

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When is a transistor and necessary?

• Desire to control a device with moderate to high
  current draw
• Microcontroller can put out 5V but typically less
  than 10 mA

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A real world example the airbag testing center
at JCI

• A much more expensive boards (National
  Instruments 1000-5000)
• Similar current limitations

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System description

• Environmental chamber
• High speed cameras
• High intensity lights
• Thermal couples
• Pressure transducers

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Why were transistors necessary?

• To make the system easy to use
• To minimize the heating up of the instrument
  panel by the high intensity lights
• Second generation airbags require deploying the
  two stages of the airbag approximately 10ms apart

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Airbag Control Black Box
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Stage 1 Fire/Trigger Circuits
5V
5V
Connection from Labview (DACOUT0)
Shunt closing to ground
R2
R2
x4 (there are 4 of these transistors one
triggers Labview and the others trigger the 3
cameras)
R3
R1a
C
B
NPN Transistor 1
R1b
E
R3
Stage 1 Fire Signal (to gray relay box)
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Analog Output/Trigger Circuitry DACOUT
Connections from Labview
Stage 1 NPN Transistor 2 (x4)
Stage 2 NPN Transistor
Stage 1 PNP Transistor
Stage 1 NPN Transistor 1
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BJT switching circuit design

• How much current do you need?
• How much current can you supply?

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BJT current multiplication considerations

• Typically desire VCE to be small
• iBASE must be large enough to cause saturation

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Example Circuit
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Example BJT Circuit
5V
To V voltage source
5V
Control signal input
RLOAD
iCONTROL
VLOAD
iLOAD
?4.3 V
c
R1
iBASE
b
VCE
VSAT?0.7 V
e
R2
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Experimental BJT Results
RLOAD
iLOAD
VLOAD
Results from using Motorola 2N2222 transistor
with RLOAD50W and R2??
iBASE
R1
VCE
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Experimental BJT Results
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Example MOSFET Circuit
VDS and iGATE are very small VDS ? 0.04 V iGATE
lt0.01mA (R1 is arbitrary)
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MOSFET Circuit 2 defaults to off position
To V voltage source
RLOAD
Control signal input
VLOAD
iLOAD
R1?R2/10
D
R1
iGATE
VDS? 0.2V
G
R2
S
iGATE is still very small
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Experimental MOSFET Results
To V voltage source
RLOAD
VLOAD
iLOAD
D
iGATE
VDS
Control signal input
G
R1
VDS and iGATE are very small VDS ? 0.04 V iGATE
lt0.01mA (R1 is arbitrary)
S
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68HC11 BJT Example
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68HC11 BJT Example
To V voltage source
Control signal input
RLOAD
R1
c
R1
b
R2
e
Control input connection
Collector-load connection
R2
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68HC11 MOSFET Example
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68HC11 MOSFET Example
Drain-load connection
R2
R1
Control input connection
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68HC11 Example
Code to turn load off ORG 1040 LDAA 00001
100 STAA 1009 LDAA 00000000 STAA 1008
SWI END
Code to turn load on ORG 1060 LDAA 0000110
0 STAA 1009 LDAA 00001100 STAA 1008 S
WI END
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MOSFET vs. BJT

• BJT
• Cheaper (?0.06)
• Can be made to handle more voltage and current
• MOSFET
• More expensive (?0.60)
• Faster
• Less power dissipated during use
• Less current draw from MPU
• Simpler circuit design

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Summary

• A mechanical engineer can use transistors to
  solve practical problems with limited knowledge
  of electronics.
• MOSFETs should be first choice for logic level
  applications.

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References

• TEXTS
• Amos, S. Principles of Transistor Circuits. Eigth
  Ed. London Butterworth-Heinemann, 1994.
• Bolton, W. Mechatronics. 2nd ed. England
  Prentice Hall, 1999.
• Mohan, Underland and Robbins. Power Electronics
  Converters, Applications, and Design. 2nd ed. New
  York John-Wiley Sons, 1995.
• Sedra, Adel, and Kenneth Smith. Microelectronics
  Circuits. Fourth ed. New York Oxford, 1998.
• WEBSITES
• Berkeley Multimedia Research Center
  http//bmrc.berkeley.edu/courseware/ICMfg92/
• Fairchild Semiconductor http//www.fairchildsemi.
  com
• HowStuffWorks.com http//howstuffworks.lycoszone.
  com/diode.htm
• Intel Corp http//www.intel.com/education/teachte
  ch/learning/transworks/flat2.htm
• Lucent Technology http//www.lucent.com/minds/tra
  nsistor/tech.html
• University of Maryland http//www.csee.umbc.edu/
  plusquel/vlsiII/slides/diode1.html