Page 102

CHAP. 5]

5.16

91

AMPLIFIERS AND OPERATIONAL AMPLIFIER CIRCUITS

(a) Find the The´venin equivalent of the circuit to the left of nodes A-B in Fig. 5-39(a) and then find v2 for Rl ¼ 1 k, 10 k, and 1. (b) Repeat for Fig. 5-39(c) and compare with part (a). (a) The The´venin equivalent of the circuit in Fig. 5-39(a) is shown in Fig. 5-39(b).

Fig. 5-39 vTh ¼

6 ð15Þ ¼ 10 V 6þ3

and

RTh ¼

ð3Þð6Þ ¼ 2 k 3þ6

By dividing vTh between RTh and Rl we get v2 ¼ For Rl For Rl For Rl The output

¼ 1 k, ¼ 10 k, ¼1 v2 depends on

Rl ð10Þ Rl þ 2

v2 ¼ 3:33 V v2 ¼ 8:33 V v2 ¼ 10 V Rl . The operation of the voltage divider is also affected by Rl .

(b) The The´venin equivalent of the circuit in Fig. 5-39(c) is shown in Fig. 5-12(d). vTh ¼ 10 V

and

Here we have

RTh ¼ 0

and v2 ¼ vTh ¼ 10 V for all values of Rl , that is, the output v2 depends on R1 , R2 , and vs only and is independent of Rl .

Mahmood_Nahvi_eBook_Schaum_s_Outlines_Theory_An  
Mahmood_Nahvi_eBook_Schaum_s_Outlines_Theory_An  
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