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CLASS B PUSH PULL AMPLIFIER


The circuitry for the Class B Push-Pull amplifier operation is the same as that for the Class A operation except that the device are biased at cutoff.

ADVANTAGES OF CLASS B PUSH PULL AMPLIFIER OVER CLASS A

It is possible to obtain greater power output. Class B power amplifier provides practically 4 times the power supplied by a single ended amplifier provided load resistance remains the same

It gives higher operating efficiency (theoretically 78.5%). It is primarily due to the fact that no power is drawn by the circuit under Zero signal condition.

Because of above advantages, a push-pull class B transistor circuit is preferred in systems Where the power supply is limited, such as those operating from solar cells or battery. The automatic cancellation of all even order harmonics from the output makes class B push-pull amplifiers highly desirable communication sound equipment.


DRAWBACKS OF CLASS B PUSH-PULL AMPLIFIER
  • The Harmonic distortion is Higher.

  • Self Bias cannot be used

  • Supply Voltage must have good regulation
CIRCUIT DIAGRAM OF CLASS B PUSH-PULL AMPLIFIER

Class B push Pull amplifier circuit

CIRCUIT OPERATION OF CLASS B PUSH-PULL AMPLIFIER
When the input signal is applied, the center tapped secondary of the input transformer develops two signals which are identical but in phase opposition. The transistors Q1 and Q2 are driven by these two signals. Thus when V1 is going positive, V2 going negative , so that transistor Q2 is being biased further off when transistor Q1 is being biased on. As the collector current in Q1 increases from Zero, it produces a half sine wave of Voltage across the upper half of the primary of the output transformer. When the positive half cycle of the input signal to Q1 begins to go negative, the signal at Q2 base is commencing to go to positive. Thus as Q1 becames biased off again, Q2 is biased on and a half cycle of Voltage wave form is generated across the lower primary winding of output transformer. The effect of the two half cycles in separate halves of the primary of output transformer is to produce a magnetic flux in the transformer core, which flows first in one direction and then in opposite direction. This flux links with the secondary of the output transformer and generates a complete sine wave output and passed on to the load.

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