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POWER AMPLIFIERS… Cont

POWER AMPLIFIERS… Cont. Why is class A so inefficient ?. Single transistor can only conduct in one direction. D.C. bias current is needed to cope with negative going signals. 75 % (or more) of the supplied power is dissipated by d.c. Solution : eliminate the bias current.

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POWER AMPLIFIERS… Cont

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  1. POWER AMPLIFIERS…Cont

  2. Why is class A so inefficient ? • Single transistor can only conduct in one direction. • D.C. bias current is needed to cope with negative going signals. • 75 % (or more) of the supplied power is dissipated by d.c. • Solution : eliminate the bias current.

  3. CLASS B Characteristics

  4. CLASS B Amplifier

  5. Push-Pull AMPLIFIER

  6. Class B push-pull ac operation.

  7. CLASS B Amplifier Operation

  8. OUTPUT WAVEFORM

  9. Working

  10. Class B O/P Characteristics Curve on Load Line

  11. Advantage over Class A Amplifier

  12. CROSSOVER DISTORTION

  13. Illustration of crossover distortion in a class B push-pull amplifier. The transistors conduct only during the portions of the input indicated by the shaded areas.

  14. CROSSOVER DISTORTION…Cont

  15. Class AB Amplifier • Class AB is probably the most common amplifier class currently used in home stereo and similar amplifiers. • Class AB amps combine the good points of class A and B amps. • They have the improved efficiency of CLASS Bamps and distortion performance that is a lot closer to that of a CLASS A amp.

  16. CLASS AB AMPLIFIER OUTPUT WAVEFORM

  17. Class C Amplifier • Class C amps are never used for audio circuits. • They are commonly used in RF circuits. • Class C amplifiers operate the output transistor in a state that results in tremendous distortion (it would be totally unsuitable for audio reproduction).

  18. CLASS C AMPLIFIER OPERATION (non inverting).

  19. Basic class C operation.

  20. CLASS C WAVEFORMS.

  21. POWER AMPLIFIER CLASSES

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