18 Figure9 Circuit Diagram of Audio Amplifier 412 Related Graphs Figure10 Input

18 figure9 circuit diagram of audio amplifier 412

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Figure.9. Circuit Diagram of Audio Amplifier 4.1.2. Related Graphs Figure.10. Input signal to Common Collector Figure.11. Output of Common Collector 19
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Figure.12. Output of Common Emitter Figure.13. Output of Class AB when Input was CE output Figure.14. Current through Load 20
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Figure.15. Power (Peak) Dissipation in Load 4.2. Practical Results The practical results of output voltage of each stage, voltage across load and current through load (speaker) were calculated and observed using Oscilloscope and DMM. The practical graphs of voltage of each stage are given below; 4.2.1. Output Voltage of CC The input of Common Collector was 100mV and its output was also 100mV as it is a voltage buffer amplifier. The practical graph using oscilloscope is shown in figure.16. 4.2.2. Output Voltage of CE The input of Common Emitter was output of Common Collector. The maximum output of this stage was 9.6V as it is a voltage amplifier. The practical graph using oscilloscope is shown in figure.17. 4.2.3. Output Voltage of Class AB (Cascaded) The input of Class AB output stage was input of output of Common Emitter stage. The maximum value of voltage (when all stages were cascaded) was 8.2V. The practical graph using oscilloscope is shown in figure.18. 21
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4.2.4. Voltage and Current of Load (Speaker) The voltage across load (speaker) was 8.2V when input from function generator was 100mV and current through this was about 0.90A. The graph of voltage across load using oscilloscope is shown in figure.19. Graph of output voltage signal across speaker when input was an audio signal is shown in figure.20. Figure.16. Output signal CC Amplifier Figure.17. Output signal of CE Amplifier 22
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Figure.19. Output signal of Class AB Figure.20. Output signal across Speaker when Input was an audio signal 4.2.5. Power and Efficiency The maximum output power was 8.2W when input of 100mV from function generator was applied to common collector stage. The practical efficiency was 61.65%. All these values and calculation can be seen in Appendix 5. Discussion Efficiency and flaws not to achieve full efficiency 23
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The efficiency of the design is calculated to be 61% but the theoretical efficiency of the class AB is found to be 75%. The reasons in the difference in the efficiencies can be; 1. The theoretical efficiency is calculated to be 75% when Biasing Voltage (V CC ) approaches output voltage (V O ) i.e. V O =V CC. 2. In theoretical calculations the power dissipation in the biasing resistances is not considered but some amount of power is dissipated in the biasing resistances. 3. The Darlington and complementary pairs we used in our design are not in a single package but made from two power transistors (TIP31C & TIP32C) so, due to this mismatching may occur which can affect efficiency. Noise cancellation 1. A capacitor is used with the power supply to cancel out the low frequency A.C noise coming from the supply 2. It is important that bypass capacitor should be closer to the power supply because longer traces of wire will increase the inductance and lower the frequency of bypass track.
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  • Fall '19
  • XYZ
  • Electronic amplifier, Common emitter

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