Power Amplifiers, Class A, Class B, Class C, Complementary Symmetry Amplifiers, Push-Pull Amplifiers, Class AB, Cross-over Distortion

1. E L E C T R O N I C C I R C U I T S I I
U N I T 5 - P O W E R A M P L I F I E R S & D C
C O N V E R T E R S
P R E S E N T E D BY
D R . R . S E N T H I L K U M A R
A S S I S TA N T P R O F E S S O R
D E PA R T M E N T O F E L E C T R O N I C S A N D C O M M U N I C AT I O N E N G I N E E R I N G
I N S T I T U T E O F R O A D A N D T R A N S P O R T T E C H N O LO G Y
E R O D E , TA M I L A N D U

2. TOPICS
• Power amplifiers- Introduction
• Class A power amplifier
• Class B power amplifier
• Class AB power amplifier
• Class C power amplifier
• Power MOSFET
• Temperature effect
• Class AB Power amplifier using MOSFET
• DC/DC converters - Introduction
• Buck converter
• Boost converter
• Buck-Boost converter

3. PART I - POWER AMPLIFIERS -INTRODUCTION
For large signal or power, amplifiers handle large voltage
signals and current levels, the main factors are:
• Efficiency
• maximum power capability
• impedance matching to the output device.
The power amplifiers satisfy these factors.

4. AMPLIFIER TYPES
Class A : The amplifier conducts through the full 360 degrees of the input. The Q-point
is set near the middle of the load line.
Class B: The amplifier conducts through 180 degree of the input. The Q-point is set at
the cutoff point.
Class AB: The amplifier conducts between 180 degree and 360 degree. The Q-point is
located between the mid-point and cutoff.
Class C: The amplifier conducts less than 180 degree of the input. The Q-point is
located below the cutoff level.

5. CLASS A AMPLIFIER
The output of a class A amplifier conducts for the full 360 degree
of the cycle.
The Q-point is set at the middle of the load line so that the AC
signal can swing a full cycle.
Maximum and minimum limit of DC load line set by the DC bias
VCC.
Efficiency 25%
to 50%

6. CLASS B AMPLIFIER
 A class B amplifier output conducts only for 180 degrees or
one half of the AC input signal.
 The Q-point is at 0 volts on the load line, so that the AC
signal can only saving for one-half cycle.
 Efficiency approximately 80%

7. CLASS AB AMPLIFIER
The Q point is above that of class B but below class A.
The output conducts between 180 degree and 360 degree of the AC
input signal.
 between 50 % and 80%

8. CLASS C AMPLIFIER
The output of class conducts less than 180 degree of the AC cycle.
The Q point is below cutoff.
 Efficiency greater than 80%