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ANALOG COMMUNICATIONS LAB

MINI-PROJECT

CLASS-D AUDIO POWER AMPLIFIER USING 555

TIMER

AIM:

To obtain audio amplification using NE555 and transistor BC 547.

COMPONENTS USED:

S.No Name of the component Specifications Qty

1) Electret MIC 1

2) Transistor BC547 1

3) IC NE 555 14) Resistors 100k, 10k,

47k, 680k,

1k

One No. each

5) Capacitors 0.1uF,

1uF,0.01uf

6) Speaker 8 1

7) Battery 9v 1

8) Breadboard 19) Connecting wires As required for

connections

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CIRCUIT DIAGRAM:

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WORKING PRINCIPLE:

In its most simplistic form an amplifier can be built with a single 555 timer. In this

project, a 200mA of current capability is enough to drive a small speaker, whichmakes it a good replacement for a low power amplifier. But when more power is

needed to allow listening music in a small room then a high power stage needs tobe added with it.

The Condenser MIC converts the sound to appropriate electrical signals. The

output of the microphone is amplified by the transistor T1. Capacitor C1 blocks the

DC component from the microphone. Resistor R1 is used to bias the condenser

microphone. R2 & R3 provides the required biasing for the transistor T1. The Vccto collector of T1 is supplied from Pin no. 5 of 555 which is at 2/3Vcc.

555 timer IC is used as a square wave oscillator with 50% duty cycle.

The amplified microphone signal is applied to pin no 5 of 555 which is areference voltage point of Threshold comparator of 555. So the audio signal

produces Pulse width modulation (PWM) of Square wave at Pin no.3.

The value of the component used in the circuit causes 555 to oscillate at

approximately 72 KHz. The speaker cannot respond to this high frequency. Instead

it responds to Pulse Width Modulated Audio signal. C4 blocks the DC component

at the output of Pin No.3 and C5 bypasses the high frequency

72 KHz carrier signal to ground.

This project explains how 555 timer IC can be used as power width

modulator to modulate the audio signal. The same principle is used in Class-D

power amplifier where the efficiency is more than 80%. Class D amplifiers workby generating a variable duty cycle square wave of which the low-frequency

portion of the spectrum is essentially the wanted output signal, and of which the

high-frequency portion serves no purpose other than to make the wave-form binary

so it can be amplified by switching the power devices.

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ADVANTAGES:

The circuit is simple and easy to construct. It is easy to operate.

DISADVANTAGES:

The IC gets heated up easily when used for longer time. Care should be taken with speaker and MIC

APPLICATIONS:

Can be used as an audio amplifier Can be used in demonstrating the pulse width modulation

PROBLEMS FACED:

The ic gets heated up easily and needed to careful while working

All the frequencies may not be amplified by using this circuit.RESULT:

Audio amplification is obtained by using BC 547 transistor and IC

NE555.