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BJT, AC behavior

BJT, AC behavior. Bollen. BJT AC behaviour DC & AC signals Characteristics DC input characteristics AC input characteristics How to draw and ac circuit Configurations Common Emitter Examples Calculating. BJT Impedance reflection p 171 Input/output resistance Source resistiance

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BJT, AC behavior

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  1. BJT, AC behavior Bollen

  2. BJT AC behaviour DC & AC signals Characteristics DC input characteristics AC input characteristics How to draw and ac circuit Configurations Common Emitter Examples Calculating BJT Impedance reflection p 171 Input/output resistance Source resistiance CE example Common Collector Example Calculations Common Base Example Calculations AGENDA Bollen

  3. Signal operation can be seen as a small variation on the DC bias of a circuit. If the signals are very small to the DC bias, transistor parameters can be considered as constant. While the BJT is a non-lineair behavior component this appoximation is only valid for very small variations on the DC-bias point. The first thing to do is to explain the AC model of a BJT, afterwards we make applications an calculations on a complete AC circuit. BJT, AC behavior P.J.F. Paap P.J.F. Paap Bollen

  4. BJT, DC & AC signals Bollen

  5. BJT, DC & AC signals Bollen

  6. DC model ac model BJT, characteristics DC model; Vbe = 0V7 Ube, Uce, Ic, Ib, Ie Capitals ac model; re = 26mV/Ie ube, uce, ic, ib, ie Low cases Bollen

  7. BJT, DC input characteristics Vbe = 0V7 Bollen

  8. BJT, AC input characteristics re = 26mV/Ic The dynamic resistor can be calculated by the DC current Ic Bollen

  9. BJT, characteristics Bollen

  10. 1 Kill all DC sources (ΔU = 0 V) replacing each dcvoltage source with a short circuit and each dccurrent source with an open circuit 2 Replace all Capacitors ( xc = 1/2.pi.f ) 3 Use the ac model of the active devices T model for BJT BJT, how to draw an ac circuit 1/4 Bollen

  11. 1 Kill all DC sources (ΔU = 0 V) replacing each dcvoltage source with a short circuit and each dccurrent source with an open circuit BJT, how to draw an ac circuit 2/4 Bollen

  12. 2 Replace all Capacitors ( xc = 1/2.pi.f ) BJT, how to draw an ac circuit 3/4 Bollen

  13. 3 Use the ac model of the active devices, T model for BJT BJT, how to draw an ac circuit 4/4 Bollen

  14. 1 Common Emitter Input = base Output = collector 2Common Collector Input = base Output = emitter or Emitter follower 3Common Base Input = emitter Output = collector BJT, configurations Bollen

  15. BJT, CE examples Bollen

  16. BJT, CE calculating Law of Bollen here ix = ib Bollen

  17. Ib does NOT flow through Rb • When Rb changes in value, base current will NOT change • Through re, base current & collector current • If input voltage increases, output voltage decreases BJT, CE calculating Bollen

  18. BJT, CE calculating There is NO Rb !! Bollen

  19. BJT, CE example Bollen

  20. BJT, CE example NO Rb1 en Rb2 in the formula !! Bollen

  21. BJT, CE example Bollen

  22. BJT, impedence reflection page 171 If you stand in base you see all resistors in the emitter (ß+1) magnified If you stand in emitter you see all resistors in the base 1/(ß+1) magnified Bollen

  23. BJT, input / output resistance Bollen

  24. BJT, input / output resistance Bollen

  25. Rs causes an attenuation in combination with the input resistance of the circuit.Then the signal is amplificated ! BJT, source resistance Bollen

  26. BJT, CE example Bollen

  27. BJT, CC example Bollen

  28. BJT, CC Bollen

  29. BJT, CC Bollen

  30. BJT Bollen

  31. BJT, CB Bollen

  32. BJT, CB Bollen

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