Question

k) Biasing of a BJT transistor is the setting of the collector emitter voltage and the collector current to the desired dc values. These voltages and currents determine the operating point (quiescent point, Q point). The three circuits given in Fig. 6.4 are designed to give the same operating point 12V 12V Rc Rc 12V R1 ?1 Rc R1 ?? Figure 6.4 a. Obtain the expression for VC in terms of the transistor parameters ?, VBE, Ico and the circuit element for each 3 circuit.

Answer 1

Redraw the circuit by representing loop currents. 12V Rc R1 CE Figure 1 Apply Kirchhoff's voltage law at loop 1. BE 12-Vr BE Write the relation between I, and I,. BE Apply Kirchhoff's voltage law at loop 2. CE Va =12-IR 12-VBE 12-VBE 12-β Ve

Redraw the circuit by representing loop currents. 12V Rc R1 CE Re Figure 2 Apply Kirchhoff's voltage law at loop 1. -12 + 1,8 + VRE + IB, = 0 BE Write the relation between I, and I,. 12-V, BE Apply Kirchhoff's voltage law at loop 2. CEE

12-V 12 -V, Since I - Redraw the circuit by apply the Thevenin's theorem 12V Rc Th CE Figure 3 Here, Th Apply Kirchhoff's voltage law at loop 1. BE

Write the relation between I, and I,. Th Apply Kirchhoff's voltage law at loop 2. CE TE CEE BE Th 12 BE Vc=12-β R.