Exercise 3.12 Biasing in a metal detector circuit


An answer:

IC = βfe βfe + 1 V E R4 V E = V B − V BE V B = V CC R2 R1 + R2 − (R!∕∕R2) ⋅ IB IB = IC βfe ⟹ IC = βfe βfe + 1 V CC R2 R1+R2 − R!∕∕R2 IC βfe − V BE R4 = βfe βfe + 1 V CC R2 R1+R2 − V BE R4 + 1 βfe+1 ⋅ R!∕∕R2

Substituting the numerical values yields IC = 0 because V B ≈ 0. Most likely R2 should be 330kΩ.