UNIT VI

POWER AMPLIFIERS : 
Classification of Amplifiers, Class A Power Amplifier, Efficiency of Class A Amplifier, Transformer Coupled Audio Power Amplifier, Push Pull Amplifier, Class B Push Pull Amplifier, Complementary Symmetry class B power amplifier, Distortion in power amplifiers, Thermal Stability & heat sinks.

REFERENCE BOOKS :

1.       Integrated Electronics – J. Millman and C.C. Halkias, McGraw-Hill, 1972.
2.       Micro Electronic Circuits – Sedra A.S. and K.C. Smith, Oxford University Press, 5th ed.
3.       Electronic Devices and Circuits - Theodore F. Bogart Jr., J. S. Beasley and G. Rico, Pearson  
          Edition,  6th Edition, 2004.
4.       Electronic Circuit Analysis and Design – Donald A. Neaman, McGraw Hill  


LECTURE  NOTES :




ASSIGNMENT - I (Theory) :

1. In what way the design features of power transistors different from small signal transistors ?

2. what is the basis for the classification of power amplifiers ? mention different types of power amplifiers ?

3. Draw the circuit for commonly used Class-A power amplifier. If the amplifier draws 10W of DC power, what is the maximum AC power available to the load ?

4. Draw the circuit for a Push-Pull amplifier and discuss its working.

5. Derive an expression for the efficiency of Class-B power amplifiers ?

6. What is harmonic distortion ? How does it arise in Class-B operation ? and how can it be corrected in Push-Pull circuit ?

7. What do you understand by Cross-over distortion ? How can it be eliminated in Class-B operation ?

8. What reasons will you assign for higher conversion efficiency of Class B-amplifier as compared to Class-A amplifier?

9. Draw a circuit for Class C- amplifier and discuss its working?

10. Among all the power amplifiers, Class C-amplifier has the maximum efficiency but its use is restricted. Give reasons.

ASSIGNMENT - II (Problems) :



Previous JNTU Questions :

1. Show that even harmonics cancel out and overall distortion reduces in a class B amplifier when connected in push-pull configuration.

2.  For a class B amplifier driven from a 24volt power supply and driving an 8 Ω load compute

      i) input power(DC)      ii) output power          iii) conversion efficiency
      if the peak-peak output voltage across the load resistance 22volts(maximum).

3. A single stage class A amplifier Vcc=20V, VCEQ  =10V, ICQ  =600mA, RL=16 Ω. 

    The ac output current varies by ± 300mA, with the ac input signal.  Find

i) The power supplied by the dc source to the amplifier circuit. ii) AC power consumed by the load resistor.

iii) AC power developed across the load resistor. iv) DC power wasted in transistor collector.

v) Overall efficiency

vi) Collector efficiency.

4. List   the   advantages  of  complementary-symmetry  configuration  over  push  pull configuration.

5. A single ended  class A power  amplifier  is coupled  to  an  8Ω load,  using  a transformer with a turn  ratio of 5:1 with a 50V supply the transistor is biased to  have a quiscent  collector  current  of 250mA. When  a sinusoidal  signal is applied to the base, the collector voltage varies between a maximum of 5V and maximum of 90V. Estimate the efficiency, power output & second - harmonic distortion  of this stage.

6.  Discuss how rectification  may takes place in a power amplifier? 









Previous GATE Questions :