2. P2: Describe two classes of amplifier
• Lesson Objectives:
• Learn the concept of amplifier
• Understand the types of power amplifier
• Describe the two class of power amplifiers
3. Amplifier
It is a circuit that increases the strength of
weak signal.
http://www.circuitstoday.com/wp-content/uploads/2010/03/How-Amplifiers-Work.gif
8. Class A amplifier
• It is a type of amplifier in which the output
flows for the full cycle of input signal.
• The conduction angle is 360 0.
• The operating point Q is at the center of load
line.
http://www.electronics-tutorials.ws/amplifier/amplifier-classes.html
9. • The biasing is such that the transistor never
goes into saturation or into cut-off region.
• Since the transistor is ON for the entire cycle
(all the time), large amount of power is
dissipated in the form of heat, hence
efficiency is less; abound 25 % only.
• Efficiency is defined as: ratio of AC power
output to the DC power input
• = AC output power/DC power input
• Applications: as a pre-amplifier
• low-power audio amplifier
10.
11. Class B amplifier
• It is a type of amplifier in which the output
flows only for the half cycle of input signal.
• The conduction angle is 180 0.
• The operating point Q is at the cut-off point of
load line.
http://www.electronics-tutorials.ws/amplifier/amplifier-classes.html
12. Class B amplifier uses two complimentary transistors:
NPN (T1) and PNP (T2).
During the positive half cycle of the input signal,
transistor T1 conducts while transistor T2 does not
conduct.
Since the Q point is at the cut-off, the output is
available for the positive half cycle only.
During the negative half cycle of the input signal,
transistor T2 conducts while transistor T1 does not
conduct.
Since the Q point is at the cut-off, the output is
available for the negative half cycle only.
Since the transistor is ON only for 180o, the efficiency
of class B amplifier is higher ; 78.50% efficiency.
