Tutorial C Power Amplifier

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Tutorial C Power Amplifier Powered By Docstoc
					                                              Tutorial 6
Q1 For the RC-coupled class-A amplifier shown in Figure 1, determine –
  (i)    the total dc power, Pi(dc) , drawn from the supply, ( 0.94W )
  (ii)   the ac load power, Po(ac) , and                     ( 50.8mW )
  (iii)  the maximum efficiency, η , of the amplifier.        ( 5.4% )
                                                       +24V


                                                            RC
                                              R1           330 Ω
                                            4.7 kΩ
                                                                     RL
                                                                    330 Ω
                                                          β = 150

                                             R2
                                            1kΩ             RE
                                                           100 Ω



                                                     Figure 1

Q2     For the Transformer-coupled class-A amplifier shown in Figure 2a, the circuit component
       values results in a dc base current of 6mA, and the input signal (Vi) results in a peak base
       current swing of 4mA. Figure 2b shown the output characteristic for the transistor T1.
       Assume the primary winding resistance and RE is very small (~ 0Ω). Determine –
       (i)    the total dc power, Pi(dc) , drawn from the supply,     ( 1.4W )
       (ii)   the dc and ac load line,
       (iii) the output compliance,
              ( 5.53V )
       (iv)   the ac power delivered to the 8Ω speaker and                 ( 0.47W )
       (v)    the maximum efficiency, η , of the amplifier.               ( 34% )
       Derive the maximum theoretical efficiency for a transformer-coupled class-A amplifier. (50%)
                      +VCC = 10V
                               N1 : N2

                                               RL = 8Ω
          R1
                                      3:1
                ib(peak) = 4mA
                IB = 6mA

 Vi                              T1

          R2
                                      RE



                           Figure 2a                                        Figure 2b
                                        Tutorial 6
Q3 For the class-AB amplifier shown in Figure 3, determine –
     (i)     the values of VCEQ, VB(Q1), VB(Q2) and     ( 10V , 10.7V , 9.3V )
     (ii)    the maximum efficiency of the amplifier. ( 78% )


                                                                +VCC = 20V

                                      R1 = 15kΩ
                                                     Q1

                                      D1


                                      D2                              RL = 32Ω
                                                     Q2

                                     R2= 15kΩ




                                             Figure 3

				
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