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Transistors
Electronics 1
CVSD
2
Transistor History
First developed in 1948 at Bell Laboratories
Originally called Transfer Resistor TRANSISTOR
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Transistor History
Drastically changed the field of electronics to how we think of electronics today.
MINIATURIZATION!!!
Replaced the vacuum tube
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Semi-Conductor Diode Review
Doping:
– P- Type material = Hole Movement (Depletion of Electrons)
– N- Type material = Carrier Movement (Excess of Electrons)
– Diodes have one PN junction
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Semi-Conductor Diode Review
Biasing:
– Forward Bias = Anode is more positive than Cathode
– Reverse Bias = Cathode is more positive than Anode
– Voltage must be high enough to overcome depletion region (Forward Operating Voltage)
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Semi-Conductor Diode Review
Elements Commonly used In Semi-conductors:– Silicon:
–Forward Bias Voltage Drop of ~ .6 volts
– Germanium:–Forward Bias Voltage Drop of
~ .3 volts HEAT SINK ALL SEMI-CONDUCTORS!
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Bipolar Junction Transistors(BJT)
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Bipolar Junction Transistors Advantages Of Transistors Over Vacuum Tubes
– Much- Smaller And Lighter– Consume Much less Power– Do Not Get Hot– More rugged – No Glass to Break– No Warm Up Time Needed
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Bipolar Junction Transistors
Disadvantages Of Transistors Over Vacuum Tubes
Can Not Handle Same Amount of Power Sensitive To Temperature and Radiation Harder To Mass Produce
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Bipolar Junction Transistors
Types of BJTs
NPN PNP Type is determined by one type of semi-conducting material
sandwiched in between two other semi-conducting materials that are both alike.
Called “Bipolar” because both holes & electrons take part in current flow
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Transistor Types
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Bipolar Junction Transistors
Because there are two junctions, transistors are generally labeled with the prefix “ 2N”:– 2N3904– 2N3906– 2N2222– 2N2907
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Bipolar Junction Transistors Schematic Symbols
NPN PNP
“Not Pointing In”
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Bipolar Junction TransistorsTerminals
Collector Base Emitter
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Bipolar Junction TransistorsTerminals
Emitter
Base
Collector
2N
3904
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Bipolar Junction TransistorsTerminals
EmitterBase
Collector
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Bipolar Junction TransistorsBias
– Base Used to control amount of collector current flow Changes the “resistance” of the transistor (E to C)
– Base-Emitter Junction Must be Forward Biased!
– Base-Collector Junction Must Be Reverse Biased!
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Bipolar Junction TransistorsNPN Junction Polarity
Two Diodes “Anode to Anode”
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Bipolar Junction TransistorsNPN Current Flow
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Bipolar Junction TransistorsPNP Junction Polarity
Two Diodes “Cathode to Cathode”
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Bipolar Junction TransistorsPNP Current Flow
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Transistor Specifications
Current GainCutoffSaturation
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Transistor Specifications Current Gain
Definition:– The ratio of base current to the
collector current.Also referred to as Beta (β) Expresses how much the transistor
is amplifying an input.
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Transistor Specifications Current Gain
Formula:
Typical Gain ~ 100Does not have any unit since it is
simply a ratio
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Current Gain Practice
Ib (E-B Current) - .5mA
Ic (E-C Current) – 70mA
β = (Ic) / (Ib)
β = 70mA (.07A) / .5mA (.0005A)
β = 140
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Transistor Specifications Current Gain
Because current flows from emitter to base and emitter to collector, the relationship of these currents are:
IE = IC + IB
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Transistor Specifications Cutoff
Definition:– Transistor is NOT conducting (No
current flow)– Occurs when the base emitter
junction is allowed to become reverse biased.
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Transistor Specifications Saturation
Definition:– Although the transistor is active
(current flow from E to C), it is the point where any increase in base current produces no further collector current gain.
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Transistor Applications
– Switching – Amplification
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Review Transistors replaced what component: BJT stands for: Draw and label the symbols for a PNP and NPN
transistor What is current Gain What is Cutoff What is Saturation What can Transistors be used for What would be the current gain for a transistor with a
E-B current of .6mA and a E-C current of 40mA