Electronics: Transistors

Caupayan. Jedda Anne G. BSEd-4

Transistors

I. Introduction

Do you wonder how hearing aid works? Do you also wonder when we use a microphone; everybody in the group can hear us? Well it is all about electronics specifically transistors.

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I. Definition

Transistors are active components and are found everywhere in electronic circuits. They are made from silicon a chemical element found in sand which does not normally conduct electricity. Transistor has two types the Bipolar Junction Transistors and Field Effect Transistors. It is also a semiconductor device that has three connections.

I. History

Transistors were invented at Bell Laboratories in New Jersey in 1947 by three brilliant US physicists: John Bardeen (1908–1991), Walter Brattain (1902–1987), and William Shockley (1910–1989).

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I. Types of Transistors

1. Bipolar Junction Transistors

-are transistors which are made up of 3 regions, the base, the collector, and the emitter.

-Current-controlled devices

-come in two main types, NPN and PNP

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a. NPN transistor -is one in which the majority current carrier are electrons.

b. PNP transistor -the majority current carrier are holes.

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Transistors are manufactured in different shapes but they have three leads (legs).

i. BASE - the lead responsible for activating the transistor

ii. COLLECTOR - the positive lead

iii. EMITTER - the negative lead

2. Field Effect Transistors

- are transistors which are made up of 3 regions, a gate, a source, and a drain

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They are used as:

Amplifiers

As amplifiers, they are used in high and low frequency stages, oscillators, modulators, detectors and in any circuit needing to perform a function.

2. Switching devices

In digital circuits they are used as switches

I. Applications

1. Microphone

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a. A transistor can be used to amplify current. This is because a small change in base current causes a large change in collector current.

b. Example is a microphone.

c. Sound waves that are fed into the microphone cause the diaphragm in the microphone to vibrate.

d. The electrical output of the microphone changes according to the sound waves.

e. As a result, the base current is varying because of the small alternating voltage produced by the microphone.

f. A small change in the base current causes a large change in the collector current.

g. The varying collector current flows into the loudspeaker. There, it is changed into the sound waves corresponding to the original sound waves.

h. The frequencies of both waves are equivalent but the amplitude of the sound wave from the loudspeaker is higher than the sound waves fed into the microphone.

2. Headphone