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C.K. Pithawalla College of Engineering & Technology - Surat

C.K. Pithawalla College of Engineering & Technology - Surat. ELECTRICAL ENGINEERING DEPARTMENT SEM 3. Group : 1. AANDANI PARAG (130090109001) ASHWANI (130090109002) AVAIYA LALEET (130090109003) PATEL HARSH (120090109006) CHAUHAN KUNJAL (120090109053). Guided By:

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C.K. Pithawalla College of Engineering & Technology - Surat

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  1. C.K. Pithawalla College of Engineering & Technology - Surat ELECTRICAL ENGINEERING DEPARTMENT SEM 3

  2. Group : 1 • AANDANI PARAG (130090109001) • ASHWANI (130090109002) • AVAIYA LALEET (130090109003) • PATEL HARSH (120090109006) • CHAUHAN KUNJAL (120090109053) • Guided By: • Prof. Parita N. Pancholi • Prof. Ankita R. Prajapati C . K . P . C . E . T

  3. Class B & Class AB amplifiers.

  4. Contents • Classification Of Power Amplifier • Operation Of Class B amplifier • Operation Of Class AB amplifier • Class B Types of class B 1)Class B - Push pull amplifier 2)Class B - Complementary symmetry amplifier • Class AB Types of class A B 1)Class AB - Push pull amplifier 2)Class AB - Complementary symmetry amplifier

  5. Classification of power amplifier • Depending on the position of Q-point on the load line. the Power Amplifier are classified into four categories.

  6. Operation of class B amplifier • A power amplifier is referred to as a class B amplifier if the output signal is obtained only for one half cycle period of the input ac signal. • As we apply a sinusoidal input signal to the base of the transistor, the B-E junction of the transistor is forward biased only during the positive half cycle of the input and base current starts flowing . • Only one half cycle is obtained at the output. Therefore the output voltage waveform is distorted • The distortion can be eliminated by using two transistors in alternate half cycle of input signals.

  7. Class B amplifier • If we use both the transistors of same type i.e. both are either p-n-p or n-p-n transistors then the configuration is known as Class B – Push pull amplifier. • This circuit is called as a push pull amplifier because. When a transistor is turned on the other conducting transistor is turned off. It is imagined that when a transistor is pushed into conduction, the conducting transistor is pulled out of conduction. Hence the name push pull amplifier. 1) Class B - Push pull amplifier

  8. Advantages & disadvantages • Advantages: 1)Higher efficiency (78.5%) 2)Zero power dissipation under quiescent condition. 3)Impedance matching with load is possible. 4)Second Harmonic component gets automatically cancelled • Disadvantages: 1)Cross Over distortion is present in the output waveform. 2)Efficiency is not so high.

  9. Class B amplifier • If we use one p-n-p and other n-p-n transistors then the configuration is known as Class B – Complementary symmetry amplifier. • This circuit does not use the driver and output transformers. Therefore it is called as transformer less Class B push-pull amplifier. 2) Class B - Complementary symmetry amplifier

  10. Advantages 1)Impedance matching with load is possible as both the transistor operate in the emitter follower configuration. 2)Transformers are not being used. This make the circuit less expensive and less bulky. 3)The practical value of %ἠmax is Higher than that of a class B push-pull amplifier as the transformers are not being used. 4)Even harmonics are automatically balanced out. Hence only the odd Harmonic are present.

  11. Operation of class AB amplifier • A power amplifier is referred to as a class AB amplifier if the output signal is obtained for more than 180° but less than 360 ° of the input ac signal. • That means the power transistor connected in class AB power amplifier will conduct for more than 180° but less than 360 ° of the ac signal. • Advantages: • The biggest advantage of class AB amplifier is elimination of the crossover distortion. • Hence this configuration is preferred in all the audio systems, radio, TV receivers etc.

  12. Class AB amplifier • The class B push-pull amplifier is connected to class AB push-pull amplifier by connecting a resistor R and diode D in the circuit as shown in fig. 1) Class AB - Push pull amplifier

  13. Class AB amplifier • The drawback of the complementary symmetry class AB circuit with resistances used for biasing can be overcome by replacing R2 by two series connected diode as shown in fig. • The voltage drop across these diodes will now forward bias the BE junction of both the transistors. 2) Class AB - Complementary symmetry amplifier

  14. Thank You!!!

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