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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 Off VBE <0.7 VIB = IC = 0
Linear VBE >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 * β2VBE = VBE1 + VBE2Slower 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 current
P-Channel – ReversedDifferent from BJT
Current flow
B
S
G
D
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 VGS > Vth
AndVDS <VGS-Vth
Transistor acts like a variable resistor, controlled by Vgs
Saturation VGS > Vth
AndVDS >VGS-Vth
Essentially constant current
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 – 10VN-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
ReferencesSpring 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