october 11, 2005me 6405 transistors me 6405 mechatronics in order of presentation: jonathan jobe...

October 11, 2005 ME 6405 Transistors

ME 6405 Mechatronics

In Order of Presentation:Jonathan Jobe

David MalphursIsaac Penny

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Contents

Brief History Properties of Transistors Types of Transistors Characteristics and Applications Engineering Selection

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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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Predecessors

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Diode Triode


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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Transistor Types

BJT Bipolar Junction Transistor

FET Field Effect Transistor

JFET (Junction FET)

MOSFET (Metal Oxide Semiconducting FET)

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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


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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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


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

VI


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


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


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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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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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

VII

VPinchoff 0001 0001


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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Transistor Selection

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Applications of Transistors

Switch

Voltage Amplifier

Current Amplifier

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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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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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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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Example Problem

Refer to your first handout

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Questions

Refer to your second handout Candy!!

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october 11, 2005me 6405 transistors me 6405 mechatronics in order of presentation: jonathan jobe...

Documents

v ce v

v bb v

r b slide

v ce reverse biased

transistors predecessors

transistors b j t s

transistors equations

selecting v bb