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Output Stages and Power Amplifiers

Output Stages and Power Amplifiers. Chapter 14 Classification of Output Stages Class A,B & AB Biasing AB Power BJT. Due today 13.4,13.14,13.23,13.27 Due Friday Nov. 16 14.8,14.11,14.27,14.37 Review Nov. 26 Quiz 3: Nov 30 Project Presentation Dec 3 and Dec 7. Schedule.

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Output Stages and Power Amplifiers

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  1. Output Stages and Power Amplifiers Chapter 14 Classification of Output Stages Class A,B & AB Biasing AB Power BJT November 9, 2007

  2. Due today 13.4,13.14,13.23,13.27 Due Friday Nov. 16 14.8,14.11,14.27,14.37 Review Nov. 26 Quiz 3: Nov 30 Project Presentation Dec 3 and Dec 7 Schedule November 9, 2007

  3. Low output resistance to deliver power w/o loss, ie. efficiency Linearity, ie. total harmonic distortion criteria Junction temperature and high power BJT Waveform shape? Introduction November 9, 2007

  4. Class AOutput Stage • Collector current waveform November 9, 2007

  5. Emitter follower Q1 biased with constant current I supplied by Q2 Transfer Characteristic of Class A November 9, 2007

  6. Transfer characteristic of the emitter follower November 9, 2007

  7. Waveforms from Class A I = VCC /RL RL = VCC/I November 9, 2007

  8. Class B • Conducts only half of the cycle November 9, 2007

  9. Maximum instantaneous power in Q1 is VCCI. Emitter follower dissipated most power when vO = 0. If RL=0, short circuit, protection? Power conversion efficiency: Power Dissipation November 9, 2007

  10. Power Efficiency Class B Power dissipation of the class B output stage versus amplitude of the output sinusoid November 9, 2007

  11. Linearity • Transfer characteristic for the class B output stage November 9, 2007

  12. November 9, 2007

  13. Opamp Implementation Op amp connected in a negative-feedback loop to reduce crossover distortion November 9, 2007

  14. Class B Single Power Supply November 9, 2007

  15. Class AB • Conduction more than half cycle November 9, 2007

  16. Transfer Function Class AB November 9, 2007

  17. Determining Output ImpedanceClass AB November 9, 2007

  18. Class AB using Diodes November 9, 2007

  19. Class AB using V_BE multiplier November 9, 2007

  20. Class AB with V_be multip+pot. The potentiometer is adjusted to yield the desired value of quiescent current in QNand QP. November 9, 2007

  21. Class C • Used in Radio frequency applications (mobile phones, radio and TV) November 9, 2007

  22. Thermal Resistance November 9, 2007

  23. Thermal Dissipation TO3 package for power transistors. The seating plane has two holes for screws to bolt it to a heat sink. The collector is electrically connected to the case. Therefore an electrically insulating but thermally conducting spacer is used between the transistor case and the “heat sink.” Dimater 2.2 cm; the outside dimension of the “seating plane” is about 4 cm. November 9, 2007

  24. Thermal Circuit Electrical analog of the thermal conduction process when a heat sink is utilized. November 9, 2007

  25. T_max: Max temperature November 9, 2007

  26. Example 14.5 November 9, 2007

  27. BJT Safe Operation November 9, 2007

  28. Variation on Class AB November 9, 2007

  29. Darlington Pair November 9, 2007

  30. Compound PNP November 9, 2007

  31. Compound PNP November 9, 2007

  32. Compound+ Darlington November 9, 2007

  33. Thermal Shutdown Protection November 9, 2007

  34. Next Class IC Power Amplifier MOSFET Power Amplifiers PSPICE Example November 9, 2007

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