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.