ME 4447/6405
Student Lecture
Justin Chow
Jacob Huang
Daniel Soledad
Overview



History
Properties
Types
 BJT
 JFET
 MOSFET

Applications
Daniel Soledad
Introduction

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 ICs

General Applications
 Amplification/Regulation
 Switches

Current Controlled
 i.e: BJT
 The output current is proportional to input current

Voltage Controlled
 i.e.: JFET, MOSFET
 The output current is proportional to input
voltage
BJT Transistor


Bipolar Junction Transistor
3 semiconductor layers sandwiched together
 Comes in two flavors
NPN BJT
PNP BJT
Justin Chow
BJT Transistor

Diodes
Forward Biased
Reverse Biased
current flows
when VPN > .6-.7V
no current flows
BJT Transistor

BJT Basics (NPN)
 BE Forward Biased
 BC Reversed Biased
 β=IB / Ic ≈ 100
 IE = IB + IC
Electron Flow
emitter
base
collector
BJT Transistor

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
Operating Region
Parameters
Cut Off
VBE <0.7 V
IB = IC = 0
Linear
VBE >0.7 V
IC = β*IB
Saturated
IB > 0, IC > 0
VBE >0.7 V,
VCE 0.2 V
BJT Transistor

Operating Regions

From
3rd Exercise

Turns on/off
coils digitally
BJT Transistor

Common Emitter Amplifier
β=100
BJT Transistor

Common Emitter Amplifier
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.
BJT Transistor

Power Dissipation
 PBJT = VCE * iCE
 Should be below the rated transistor power
 Important for heat dissipation as well

Increased Gain
β = 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
FET
Collector
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
MOSFET
In practice the body and
source leads are almost
always connected
 Most packages have these
leads already connected

D
D
B
G
G
S
B
S
JFET
D
G
S



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 current


P-Channel – Reversed
Different from BJT
Current
flow
D
G
B
S

N-Channel
 VGS > Vth -> Turns on device
 VGS < VTH -> No Current

P-Channel
 Reversed

Only E-type used now
Region
Criteria
Effect on Current
Cut-off
VGS < Vth
IDS=0
Linear
Saturation
VGS > Vth
Transistor acts like a
variable resistor,
And
VDS <VGS-Vth controlled by Vgs
VGS > Vth
Essentially constant
current
And
VDS >VGS-Vth
Current
flow
D
G
B
S
Current
flow
D
G
B
S



Used in high-power applications
Heat Sink
Vertical 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
Medium
Speed
High
Medium
Low
Noise
Moderate
Worst
Best
Good
No
Switch
High-Z Gate No
Yes
Yes
Yes
Yes
ESD
Sensitivity
More
Less
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 Slides
http://www.made-in-china.com/image/2f0j00ZhaTKREnIQkfM/IC-Transistor.jpg
http://en.wikipedia.org/wiki/JFET
http://en.wikipedia.org/wiki/MOSFET
http://en.wikipedia.org/wiki/Bipolar_junction_transistor
http://www.allaboutcircuits.com/vol_3/chpt_2/8.html
http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/images/basicbjt.gif&imgrefurl=http://www.mcmanis.com/chuck/robotics/tutorial/hbridge/bjt_theory.html
http://www.allaboutcircuits.com/vol_3/chpt_2/6.html
http://web.engr.oregonstate.edu/~traylor/ece112/lectures/bjt_reg_of_op.pdf
http://hades.mech.northwestern.edu/wiki/index.php/Diodes_and_Transistors#Com
mon_Emitter_Amplifier_Circuit
http://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