Question

Consider the following circuit, where the transistors are similar Si transistors. Given I1 = 2mA, I2 = 1μA, Vcc = 12 V, find R1 and R2.

(a) R1 = 10kΩ, R2 = 6kΩ

(b) R1 = 5.6kΩ, R2 = 20kΩ

(c) R1 =18kΩ, R2 = any value

(d) R1 = 18kΩ, R2 = 5.6kΩ

I had been asked this question by my college director while I was bunking the class.

I want to ask this question from Transistor Bias Configuration topic in division Transistor Biasing and Low Frequencies of Analog Circuits

Answer 1

The correct answer is (d) R1 = 18kΩ, R2 = 5.6kΩ

Explanation: R2 = (Vcc – VBE)/I1 = (12 – 0.7)/2m = 5.65 kΩ – Using KVL

Also, I2*R1 = VT ln(I1/I2) = 0.026 * ln(2)

Thus, R1 = 0.026*ln(2)/1μ = 18 kΩ.