# Tutorial C Power Amplifier

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```					                                              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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