Transistors Electronics 1 CVSD. 2 Transistor History First developed in 1948 at Bell Laboratories...

Transistors

Electronics 1

CVSD

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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