Please help me perform DC analysis of the attached circuit and derive equation for VB (Q1)
Make R4 = R5 = 20k. Add two more 20k resistors, one from each of the bases of Q1 &amp; Q2 to ground. Add two 10uF capacitors, one between each ac voltage source and the bases of Q1 &amp; Q2 (positive of capacitors to bases). This will bias the bases of Q1 &amp; Q2 to about mid-supply.
As the circuit stands:
CCS provides constant current of 0.7/500 = 1.4mA
This current is split equally between the two sides and so Ic of Q1 = 0.7mA
hFE of BC547B (at Ic = 2mA) is about 300 and so base current = 0.7mA/300 = 2.3uA
Voltage at base of Q1 = 9-(2.3uA * 1000k) = 6.7V
Voltage at base of Q2 will be about the same.