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# Module 2: Bipolar Junction Transistor - BJT PowerPoint PPT Presentation

Module 2: Bipolar Junction Transistor - BJT . Prepared by: Cesar Mendoza Applied Technology Teacher. Module Objectives. Upon successful completion of this module, students should be able to: State the advantages of a transistor over vacuum tubes. Define a Bipolar Junction Transistor.

Module 2: Bipolar Junction Transistor - BJT

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## Module 2: Bipolar Junction Transistor - BJT

Prepared by: Cesar Mendoza

Applied Technology Teacher

Prepared by: CESAR MENDOZA-Applied Technology Teacher

## Module Objectives

Upon successful completion of this module, students should be able to:

State the advantages of a transistor over vacuum tubes.

Define a Bipolar Junction Transistor.

Differentiate between an NPN and a PNP transistor in terms of their construction, two-diode analogy and symbols.

Identify the three different BJT terminals and state the function of each terminal.

Recognize the low-power and high-power BJTs.

Measure transistor currents, and confirm that the emitter current is the sum of the collector and base currents.

State the common applications of a Bipolar Junction Transistor.

Describe the three different BJT configurations with the help of circuit diagrams.

Describe the application of a BJT as a switch through a practical demonstration.

Build and test an ‘automatic night lamp circuit’ to demonstrate the function of a BJT as a switch.

Build and test a simple temperature control system.

Prepared by: CESAR MENDOZA-Applied Technology Teacher

## OBJECTIVE 1. State the advantages of a transistor over vacuum tubes.

The reasons are obviously its advantages over vacuum tubes such as :

compact size,

light weight,

more resistive to shocks and vibrations,

low operating voltage,

long life and so on.

Prepared by: CESAR MENDOZA-Applied Technology Teacher

## OBJECTIVE 2:Define a Bipolar Junction Transistor.

A Bipolar Junction Transistor (BJT) is defined as a three-terminal semiconductor device, whose operation depends upon the flow of electric charge carriers within the solid.

The word transistor is derived from the combination of two words, “Transfer-Resistance”. It means that it is a device, which transfers a low resistance into a circuit having high resistance.

Transistors in general are classified as bipolar or unipolar type. The bipolar type has two PN-Junctions, while unipolar types have only one PN-Junction.

Prepared by: CESAR MENDOZA-Applied Technology Teacher

## OBJECTIVE 3:Differentiate between an NPN and a PNP transistor in terms of their construction, two-diode analogy and symbols.

Prepared by: CESAR MENDOZA-Applied Technology Teacher

The three regions are called

Emitter (E),

Base (B), and

Collector (C),

and the two PN-junctions are

C-B junction and

E-B junction.

Prepared by: CESAR MENDOZA-Applied Technology Teacher

## OBJECTIVE 3: Identify the three different BJT terminals and state the function of each terminal.

C- Collector

The functions of the three regions are as follows:

E

Emitter:To emit majority charge carriers into the base.

Base:Base is the middle, extremely thin, and lightly doped region. It controls the electrons flowing to the collector.

Collector:To collect the emitted charge carriers through the base.

Base -B

E- Emitter

Prepared by: CESAR MENDOZA-Applied Technology Teacher

## OBJECTIVE 3: Recognize the low-power and high-power BJTs.

Low–power, small-signal transistors are sealed in a metal, plastic or epoxy package.

Prepared by: CESAR MENDOZA-Applied Technology Teacher

High power transistors are usually designed to be mounted onto a metal frame, which acts as a heat sink (to conduct heat away).

Prepared by: CESAR MENDOZA-Applied Technology Teacher

where IE Emitter current, IC  Collector current, and IB  Base current

## OBJECTIVE 4: Measure transistor currents, and confirm that the emitter current is the sum of the collector and base currents.

To use a BJT, we connect it so that:

Its emitter is its negative terminal.

The collector is several volts positive of its emitter.

The base is 0.7V (or slightly more) positive of its emitter.

Under these conditions, we find that:

A small base current flows into the base.

A much larger current flows into the collector.

The base and collector currents flow out of the emitter

Prepared by: CESAR MENDOZA-Applied Technology Teacher

## OBJECTIVE 4: State the common applications of a Bipolar Junction Transistor

Common applications of a transistor include the following:

A switch

An amplifier

Prepared by: CESAR MENDOZA-Applied Technology Teacher

## As a Switch

When the switch is closed,a small current flows into the base (B) of the transistor, which is just enough to make LED B glow dimly.

When the switch is open, no base current flows, so the transistor switches off the collector current.

Prepared by: CESAR MENDOZA-Applied Technology Teacher

## Transistor Amplifier:

Amplification is the process of increasing the level of a weak signal. A small change in the base current of a transistor produces a large variation in the collector current

Prepared by: CESAR MENDOZA-Applied Technology Teacher

Prepared by: CESAR MENDOZA-Applied Technology Teacher

Prepared by: CESAR MENDOZA-Applied Technology Teacher

Prepared by: CESAR MENDOZA-Applied Technology Teacher