Baiscs of an amplifier

1. P
Welcome to Lecture
Basics Of an Amplifier
Presented By: V.C Togadiya

2. What is an
Amplifier?
An amplifier is an electronic device or circuit
which is used to increase the magnitude of the
signal applied to its input

3. Introduction
Amplifier is the generic term used to describe a circuit which
produces and increased version of its input signal.
In “Electronics”, small signal amplifiers are commonly used
devices as they can amplify a relatively small input signal, for
example from a Sensor such as a photo-device, into a much larger
output signal to drive a relay, lamp or loudspeaker for example.

4. Classification of Signal Amplifier
Type of Signal Type of
Configuration
Classification
Frequency of
Operation
Small Signal Common Emitter Class A Amplifier Direct Current (DC)
Large Signal Common Base Class B Amplifier Audio Frequencies (AF)
Common Collector Class AB Amplifier Radio Frequencies (RF)
Class C Amplifier
VHF, UHF and SHF
Frequencies

5. Amplifier Gain
Voltage Amplifier Gain
Current Amplifier Gain
Power Amplifier Gain
The introduction to the amplifier gain can be said to be the relationship that exists between the signal
measured at the output with the signal measured at the input.
Different Kinds of amplifier gain:

6. Definition: Audio Power Amplifier
• An audio power amplifier (or power amp) is an electronic amplifier
that amplifies low-power electronic audio signals such as the signal
from radio receiver or electric guitar pickup to a level that is high
enough for driving loudspeakers or headphones.

7. Difference between Voltage and Power Amplifier
• Voltage Amplifiers − The amplifier circuit that increases the voltage
level of the input signal, is called as Voltage amplifier.
• Power Amplifiers − The amplifier circuit that increases the power
level of the input signal, is called as Power amplifier.

8. Based on Biasing Conditions
• Depending upon their mode of operation, there are class A, class B and
class C amplifiers.
• Class A amplifier − The biasing conditions in class A power amplifier are
such that the collector current flows for the entire AC signal applied.
• Class B amplifier − The biasing conditions in class B power amplifier are
such that the collector current flows for half-cycle of input AC signal
applied.
• Class C amplifier − The biasing conditions in class C power amplifier are
such that the collector current flows for less than half cycle of input AC
signal applied.
• Class AB amplifier − The class AB power amplifier is one which is created
by combining both class A and class B in order to have all the advantages of
both the classes and to minimize the problems they have.

9. Introduction of Power amplifier
• Power amplifiers are used to deliver a relatively high amount of power, usually to
a low resistance load.
• Typical load values range from 300W (for transmission antennas) to 8W (for audio
speaker).
• Although these load values do not cover every possibility, they do illustrate the
fact that power amplifiers usually drive low-resistance loads.
• Typical output power rating of a power amplifier will be 1W or higher.
• Ideal power amplifier will deliver 100% of the power it draws from the supply to
load. In practice, this can never occur.
• The reason for this is the fact that the components in the amplifier will all
dissipate some of the power that is being drawn form the supply.
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10. Concept of Power Amplifier
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• Provide sufficient power to an output load to drive other power device.
• To deliver a large current to a small load resistance e.g. audio speaker;
• To deliver a large voltage to a large load resistance e.g. switching power supply;
• To provide a low output resistance in order to avoid loss of gain and to maintain
linearity (to minimize harmonic distortion)
• To deliver power to the load efficiently

11. 11
Power Amplifier Power Dissipation
P1 = I1
2R1
P2 = I2
2R2
ICQ
RC
RE
R1
R2
VCC
I1
I2
ICC
PC = ICQ
2
RC
PT = ITQ
2
RT
PE = IEQ
2
RE
IEQ
The total amount of power being dissipated by
the amplifier, Ptot , is
Ptot = P1 + P2 + PC + PT + PE
The difference between this total value and the
total power being drawn from the supply is the
power that actually goes to the load – i.e.
output power.

12. Thank you