Semiconductor Devices II Transistors have revolutionized Electronics and our way of life. Before transistors, computers were bulky, expensive, slow and.

Semiconductor Devices IITransistors have revolutionized Electronics

and our way of life. Before transistors, computers were bulky, expensive, slow and highly un-reliable.

ELECTRONICS TECHNOLOGY

ELECTRONICS TECHNOLOGY

Semiconductor Devices II Transistors have revolutionized Electronics and our

way of life. Before transistors, computers were bulky, expensive, slow and highly un-reliable.

ELECTRONICS TECHNOLOGY Semiconductor Devices II

Transistors are a semiconductor device similar to diodes

Semiconductor Devices IITransistorsTransistor Biasing

ELECTRONICS TECHNOLOGY

ObjectiveIn this section we will learn:

1. configuration of the transistor,

2. Its usefulness

3. Its operating characteristics

ELECTRONICS TECHNOLOGY Transistors

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ELECTRONICS TECHNOLOGY Transistors

Configuration Transistors have two junctions instead of one as the

case with a junction diode.

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P N P NP P

Diode Transistor

ELECTRONICS TECHNOLOGY Transistors

Configuration Transistors Symbol is illustrated below. The identifier

is Q

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N P N

ELECTRONICS TECHNOLOGY Transistors

Configuration Transistors Symbol is illustrated below. The identifier is

Q. (Negative-Positive-Negative and Positive-Negative-Positive)

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Collector

Base

Emitter

Collector

Base

Emitter

NPN PNP

ELECTRONICS TECHNOLOGY Transistors

Configuration NPN Transistors have the arrow pointing outward

from the base. (Note: Never Points iN)

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Collector

Base

Emitter

NPN

Collector

Base

Emitter

PNP

ELECTRONICS TECHNOLOGY Transistors

Configuration PNP Transistors have the arrow toward the base.

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Collector

Base

Emitter

NPN

Collector

Base

Emitter

PNP

ELECTRONICS TECHNOLOGY Transistors

Configuration The emitter is heavily doped and allows for electron

flow in the semiconductor (notated by the arrow)

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Collector

Base

Emitter

NPN

ELECTRONICS TECHNOLOGY Transistors

Configuration The base is thin and is lightly doped. This configuration

allows for electron flow from Emitter to collector.

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NPN

Collector

Base

Emitter

ELECTRONICS TECHNOLOGY Transistors

Configuration The collector is moderately doped and is the largest

of the three. This allows for more heat loss.

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NPN

Collector

Base

Emitter

ELECTRONICS TECHNOLOGY Transistors

Identification The identification standard is similar to the standard

used on diodes.

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NPN

2N2222

TransistorSemiconductorPart Number

ELECTRONICS TECHNOLOGY Transistors

Pin layout The leads of a TO5 package are always configured as

shown below…

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NPN

E

B

C

(bottom side)

ELECTRONICS TECHNOLOGY Transistors

Pin layout The leads of a TO-92 package are always configured

as shown below…

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NPN

C

B

E

(bottom side)

ELECTRONICS TECHNOLOGY Transistors

Pin layout Power Transistors (type TO-3) are different. The

collector is the case

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(bottom side)

E B

Collector

(Side view)

ELECTRONICS TECHNOLOGY Transistors Biasing

Objective Understand the biasing of a transistor Define Cutoff and Saturation Define fixed, self and combinational biasing

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ELECTRONICS TECHNOLOGYTransistor Biasing

In order for a transistor to function as an amplifier, the BE junction must be forward biased.

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ELECTRONICS TECHNOLOGYTransistor Biasing

A minimum voltage VBE of .7 volts must be applied to forward bias the junction BE.

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VBE

ELECTRONICS TECHNOLOGYTransistor Biasing

In order for a transistor to work properly as an amplifier, the Collector Base (CB) junction must be reversed biased.

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ELECTRONICS TECHNOLOGYTransistor Biasing

VBC must have a voltage level greater than VBE.

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VBC

ELECTRONICS TECHNOLOGYTransistor Biasing

When VBC < VBE and reverse biased, current is forced to flow as illustrated.

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N

P

N

+++

- - -

+++

-

ELECTRONICS TECHNOLOGYTransistor Biasing

Since the base material is very small compared to the collector, only a small amount of Current flows through IB.

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N

P

N

+++

- - -

+++

-

ELECTRONICS TECHNOLOGYTransistor Biasing

With this information, IC=IB+IE.

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N

P

N

+++

- - -

+++

-

ELECTRONICS TECHNOLOGYTransistor Biasing

Once the EB junction is forward biased and CB is reversed biased, Current will flow through the Transistor.

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ELECTRONICS TECHNOLOGYTransistor Biasing

Keep in mind the base is thin and lightly doped. Therefore little current flows through the base. Most of the current flows through the collector.

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End of Presentation