October 11, 2005 ME 6405 Transistors
ME 6405 Mechatronics
In Order of Presentation:Jonathan Jobe
David MalphursIsaac Penny
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October 11, 2005 ME 6405 Transistors
Contents
Brief History Properties of Transistors Types of Transistors Characteristics and Applications Engineering Selection
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October 11, 2005 ME 6405 Transistors
History
Vacuum Tube1879 Edison Invents Light Bulb
1883 Edison found that he could detect electrons flowing through the vacuum from the lighted filament to a metal plate mounted inside the bulb. “Edison Effect”
John Fleming implements Edison Effect as first diode.
1906 Lee DeForest introduced a third electrode called the grid into the vacuum tube. The resulting triode could be used as both an amplifier and a switch.
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October 11, 2005 ME 6405 Transistors
Predecessors
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Diode Triode
October 11, 2005 ME 6405 Transistors
First Transistors
Bell Labs 1947 Invented First Transistor
Application: replace vacuum tubes Smaller, more durable, no warm up Made of Germanium
Current Transistors Silicon based
Doped with phosphorus (n-type) Doped with boron (p-type)
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The PN Junction
Forward Biasing The external Voltage lowers the potential barrier at the junction, allowing the electrons to flow.
Reverse Biasing The external voltage raises the potential barrier at the junction, preventing electrons from flowing.
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October 11, 2005 ME 6405 Transistors
Transistor Types
BJT Bipolar Junction Transistor
FET Field Effect Transistor
JFET (Junction FET)
MOSFET (Metal Oxide Semiconducting FET)
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October 11, 2005 ME 6405 Transistors
B J T s 2 types
NPN (most common)
When IB≠0, VCE
forward biased &
VBC reverse biased PNP
When IB≠0, VCE
reverse biased &
VBC forward biased
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NPN bipolar junction transistor
PNP bipolar junction transistor
October 11, 2005 ME 6405 Transistors
npn-B J T Voltage Characteristic
Cutoff: Base-Emitter starts to conduct with VBE=0.6V
Saturation: Increasing IB causes IC to rise exponentially.
Active:
Breakdown: Ic approaches infinity due to breakdown at both junctionsBIIC
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B J T Operational Characteristics
OperatioOperation Regionn Region
IB or VCE
Char. VVCECE & V & VBEBE JunctionsJunctions
ModeMode
Cutoff IB = Very small
Reverse & Reverse
Open Switch
Saturation
VCE = Small
Forward & Forward
Closed Switch
Active Linear
VCE = Moderate
Reverse &Forward
Linear Amplifier
Break-down
VCE = Large
Beyond Limits
Overload
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October 11, 2005 ME 6405 Transistors
Equations of npn-B J T s
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Definitions
Kirchoff’s Current Law
In Active region
cBE III
EBBE VVV ECCE VVV
BIIC Common values for ß are 20 to 200
October 11, 2005 ME 6405 Transistors
Point of Operation
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The existence of RC means
that IC and VCE are no
longer independent.
VCE = Vcc – IC*RC
After solving for IC,
C
CE
C
CCC R
V
R
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October 11, 2005 ME 6405 Transistors
Point of Operation
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Load-line constraint
C
CE
C
CCC R
V
R
VI
Q point for IB=100μA
Selecting VBB and VCC, we can find the operating point, or Q point.
IB = (VBB-VBE)/RB
October 11, 2005 ME 6405 Transistors
B J T resistor sizing ß and IC,max are specified by the catalog
We need to choose Values for RB and RC to keep IC
and IB within specifications
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CC
CC
VR
I
BB BBB
B C
V VR
I I
CB
II
October 11, 2005 ME 6405 Transistors
Three Types of Field Effect Transistors MOSFET (metal-oxide-semiconductor field-effect
transistors) Enhancement mode IDS α VGS
Depletion mode IDS α 1/VGS
JFET (Junction Field-effect transistors) Available in n or p Channel
n-Channel activated by VGS > 0 for MOSFET and VGS < 0 for JFET p-Channel activated by VGS < 0 for MOSFET and VGS > 0 for JFET
Most Common Types n-Channel Enhancement Mode MOSFET (NMOS) n-Channel JFET
Field Effect Transistors (FET)
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October 11, 2005 ME 6405 Transistors
Enhanced MOSFET
Depleted MOSFET
FET Architecture
BJT FET
Base Gate
Collector Drain
Emitter Source
JFET
Analogous BJT Terminals
Conducting
Region
Nonconducting
Region
Nonconducting
Region
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October 11, 2005 ME 6405 Transistors
NMOS Voltage Characteristic
Active Region
Saturation Region
VGS < Vth
IDS=0VGS > Vth :
0 < VDS < VPinch off
Active Region IDS controlled by VGS
VDS > VBreakdown
IDS approaches IDSShort
Should be avoided
VDS > VPinch off
Saturation RegionIDS constant
VDS = Constant
2
1
TH
GSDSSHORTDS V
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VPinchoff 0001 0001
October 11, 2005 ME 6405 Transistors
Junction Field Effect Transistor
VGS > Vth
IDS=0
VGS < -Vth : 0 < VDS < VPinch off
Active Region
IDS controlled by VGSVDS > VPinch off
Saturation RegionIDS constant
VDS > VBreakdown
IDS approaches IDSShort
Should be avoided
Difference from NMOS
VPinchoff
Active Region
Saturation Region
2
1
TH
GSDSSHORTDS V
VII
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October 11, 2005 ME 6405 Transistors
Transistor Selection
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October 11, 2005 ME 6405 Transistors
Applications of Transistors
Switch
Voltage Amplifier
Current Amplifier
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October 11, 2005 ME 6405 Transistors
Transistor as a Switch
Many times you just need to switch a signal on or off
Ex. Digital Logic, LED’s, PWMRelays can perform this same function
They can usually handle higher currents than can transistorsNot Solid State, so shorter life and less durableSlower activation time
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October 11, 2005 ME 6405 Transistors
Other times you want to amplify an analog signal
Ex. Sensor input, audio, Op-amps can perform the same function
Higher gainsCan’t handle nearly as much current.
Thus Op-amps are better for signal amplification, while Transistors are better for power amplification.
Transistor as a Voltage Amplifier
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October 11, 2005 ME 6405 Transistors
Transistor as a Current Amplifier
Other times you want to amplify an analog signal
Ex. Sensor input, audio, Op-amps can perform the same function
Higher gainsCan’t handle nearly as much current.
Thus Op-amps are better for signal amplification, while Transistors are better for power amplification.
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October 11, 2005 ME 6405 Transistors
Example Problem
Refer to your first handout
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October 11, 2005 ME 6405 Transistors
Questions
Refer to your second handout Candy!!
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