Justin ChowJacob HuangDaniel Soledad

ME 4447/6405Student Lecture

HistoryPropertiesTypes 　

BJT JFET MOSFET

Applications

Overview

Daniel Soledad

Transistor History “Transistor” is combination of

“transconductance” and “variable resistor”

How Transistors Are Made▪ Vacuum tubes

▪ Inefficient, fragile, bulky, generated a lot of heat

▪ First Transistors▪ Semiconductors – Bell Labs 1947

Introduction

Packaging Surface Mount or Through Hole Usually 3 or 4 terminal device

▪ Can be packaged into ICsGeneral Applications

Amplification /Regulation Switches

Introduction

Current Controlled i.e: BJT The output current is proportional to

input currentVoltage Controlled

i.e.: JFET, MOSFET The output current is proportional to

input voltage

Bipolar Junction Transistor3 semiconductor layers sandwiched

together

Comes in two flavors NPN BJT PNP BJT

BJT Transistor

Justin Chow

DiodesForward Biased Reverse Biased

current flows no current flows

when VPN > .6-.7V

BJT Transistor

BJT Basics (NPN) BE Forward Biased BC Reversed Biased β=IB / Ic ≈ 100

IE = IB + IC

BJT Transistor

emitter base collector

Electron Flow

Things to remember PNP, biasing opposite Conventional current vs electron flow A small input current controls a much

larger output current.

BJT Transistor

Operating Regions

BJT Transistor

Operating Region

Parameters

Cut OffVBE <0.7 VIB = IC = 0

LinearVBE >0.7 VIC = β*IB

SaturatedIB > 0, IC > 0VBE >0.7 V,VCE 0.2 V

Operating Regions

BJT Transistor

From3rd Exercise

Turns on/off coils digitally

Common Emitter Amplifier

BJT Transistor

β=100

Common Emitter Amplifier

BJT Transistor

IB = (Vin − VB) / 10000Ω = (Vin − 0.7) / 10000Ω IC = β(Vin − 0.7) / 10000Ω

Vout=10000*(Vin-0.7)/1000

When VCE = 0.2V IC = 9.8 / 1000Ω = 9.8mA IB = IC / β = 0.098mA Vin − 0.7 = (0.098mA)(10000Ω) Vin = 1.68V or greater.

Power Dissipation PBJT = VCE * iCE

Should be below the rated transistor power

Important for heat dissipation as well

BJT Transistor

Increased Gainβ = β1 * β2

VBE = VBE1 + VBE2

Slower Switching

2N6282

Analogous to BJT Transistors

Output is controlled by input voltage rather than by current

4 Pins vs. 3

BJT FETCollector Drain

Base Gate

Emitter Source

N/A Body

FET (Field Effect Transistors) MOSFET (Metal-Oxide-Semiconductor Field-

Effect Transistor) JFET (Junction Field-Effect Transistor) MESFET HEMT MODFET

Most common are the n-channel MOSFET or JFET

Jacob Huang

In practice the body and source leads are almost always connected

Most packages have these leads already connected

B

S

G

D

B

S

G

D

S

G

D

MOSFET

JFET

Metal-Oxide Semiconductor F.E.T. A.K.A. Insulated-Gate FET (IGFET) 2 Modes: Enhancement/Depletion

N-Channel + Vgs -> More electrons -> More Current

- Vgs -> Less electrons -> Less currentP-Channel – ReversedDifferent from BJT

Current flow

B

S

G

D

N-Channel VGS > Vth -> Turns on device

VGS < VTH -> No CurrentP-Channel

Reversed

Only E-type used now

Region Criteria Effect on Current

Cut-off VGS < Vth IDS=0

Linear VGS > Vth

And

VDS <VGS-Vth

Transistor acts like a variable resistor, controlled by Vgs

Saturation VGS > Vth

And

VDS >VGS-Vth

Essentially constant current

Current flow

B

S

G

D

Current flow

B

S

G

D

Used in high-power applicationsHeat SinkVertical layout

Not Planar like other transistors

Reverse Bias VGS => Reduces channel size => Reduced Current

Defaults “on”

Vgs = 0 “on”

|Vgs|> |Vp| “off”

Vp = Pinch-off or Cut-off Voltage

Internal Capacitance

Bi-directional

Cut-off voltage is varying for each JFET 0.3V – 10V

N-Channel – Negative VGS P-Channel – Positive VGS

Do not Forward Bias JFET – burn out

Property

BJT MOSFET

JFET

Gm Best Worst MediumSpeed High Medium LowNoise Moderat

eWorst Best

Good Switch

No Yes Yes

High-Z Gate

No Yes Yes

ESD Sensitivity

Less More Less

Complementary MOS Used in Logic Gates P-channel (PMOS) to high N-channel (NMOS) to low

HIGH usually +5 V LOW usually ground

Q is high when A = 0, Q is low when A = 1

References

Spring 2007/2008 Slideshttp://www.made-in-china.com/image/2f0j00ZhaTKREnIQkfM/IC-Transistor.jpghttp://en.wikipedia.org/wiki/JFEThttp://en.wikipedia.org/wiki/MOSFEThttp://en.wikipedia.org/wiki/Bipolar_junction_transistorhttp://www.allaboutcircuits.com/vol_3/chpt_2/8.htmlhttp://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/images/basic-bjt.gif&imgrefurl=http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt_theory.htmlhttp://www.allaboutcircuits.com/vol_3/chpt_2/6.htmlhttp://web.engr.oregonstate.edu/~traylor/ece112/lectures/bjt_reg_of_op.pdfhttp://hades.mech.northwestern.edu/wiki/index.php/Diodes_and_Transistors#Common_Emitter_Amplifier_Circuithttp://en.wikipedia.org/wiki/Darlington_transistor http://www.allaboutcircuits.com/vol_3/chpt_6/2.html http://www.allaboutcircuits.com/vol_3/chpt_4/2.html http://www.designers-guide.org/Forum/YaBB.pl?num=1162476437/4 http://en.wikipedia.org/wiki/CMOS