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For a NPN transistor in CE mode voltage divider bias configuration determine VC and Vs.

Given VCC = +20V, VEE= -20V, Ri = 8.2KΩ, R2 = 2.2KΩ, RC = 2.7KΩ, RE = 1.81KΩ, C1=C2 = 10µF and β = 120.

Mumbai University > Electronics and telecommunication engineering > Sem 3 > Analog electronics 1

Marks: 10M

Years: May 15

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enter image description here

The Thevenin resistance and voltage are determined for the network to the left of the base terminal as shown in fig (a) and (b).

Rth=R1||R2 = 8.2K || 2.2K = 1.73 kΩ

enter image description here

I = (VCC+VEE)(R1+R2)=(20+20)(8.2k+2.2k)=(40V)(10.4K) = 3.85 mA

Vth=IR2VEE= 3.85 mA x 2.2 kΩ - 20 V

= -11.53 V

By redrawing network as shown in fig and apply KVL,

enter image description here

Substituting IE = (1+β) IB gives,

V_EE-V_th - V_BE- (1+β) I_B R_E - I_B R_th = 0

I_B = \frac{(V_EE -V_th - V_BE)}{( R_th+ (1+β) R_E )}

= \frac{(20-11.53-0.7)}{(1.73 k+121x1.8k)} = \frac{(7.77 V)}{(219.53 k)} = 35.39 µA

I_C= βI_B = 120 x 35.39 µA = 4.25 mA

V_C = V_CC - I_C R_C

= 20 V – (4.25 mA)(2.7k)

= 8.53 V

V_B = -V_th - I_B R_th

= -11.53 V – 35.39µA x 1.73k

= -11.59 V

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