
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
I = (VCC+VEE)(R1+R2)=(20+20)(8.2k+2.2k)=(40V)(10.4KΩ) = 3.85 mA
Vth=IR2−VEE= 3.85 mA x 2.2 kΩ - 20 V
= -11.53 V
By redrawing network as shown in fig and apply KVL,
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