Question

Considering all transistors to be similar and β is very large, when I1 = 10 mA, find current I2.

(a) 10 mA

(b) 50 mA

(c) 25 mA

(d) 20 mA

The question was asked in my homework.

This intriguing question originated from Transistor Bias Configuration in chapter Transistor Biasing and Low Frequencies of Analog Circuits

Answer 1

Correct choice is (c) 25 mA

For explanation I would say: Let current through the transistor Q1/Q2 be IC. Since both are similar, we can say that,

 IC = I1/2

Similarly, current through transistors Q3 to Q7 is assumed to be IC’, where IC’ = I2/5

Since all transistors are similar. IC = IC’

I2 = 5IC’ = 5 IC = 2.5*I1.