1. Load Line & BJT Biasing

2. DC Biasing To establish a constant dc collector current in the BJT. Biasing is required to operate the transistor in the linear region. The DC bias point in i C -v CE plane should be such that maximum output signal swing is achieved. Ideally the I C and V CE in a biased circuit should remain constant. Practical circuit bias point is affected by the change in  and temperature changes. Q point should be insensitve to variations in temperature and current gain beta.

3. Effect of  Ideally the  is considered as a constant value. (say  =100) In practise, the precise current gain of each transistor is not known. The maximum and minimum values of the current gain  can be obtained from the manufactureres data sheet. In designing BJT circuit  max and  min must be used to calculate the range of possible I c and V CE. So, change in  results in change in operating point.

4. replace the capacitors with an open-circuit equivalent because the reactance of a capacitor for dc is ∞Ω The dc supply V cc can be separated into two supplies Fixed bias circuit DC equivalent Fixed Base Bias

5. Write KVL equation in the clockwise direction of the loop : +V CC – I B R B – V BE =0 Solving the equation for the current I B results : Base-emitter loop Forward Bias of Base-emitter

6. The magnitude of the I C is related directly to I B through I C =βI B Apply KVL in the clockwise direction around the indicated close loop results: V CE +I C R C -V CC =0 V CE = V CC -I C R C Recall that : V CE = V C - V E In this case, V E = 0V, so V CE =V C V BE =V B -V E Than V E =0V, V BE =V E Collector–emitter loop Collector-emitter loop

7. Determine the value of Q-point for this figure. Also find the new value of Q-point if  change to 150.

8. Voltage divider bias

9. Step 1: The input side of the network can be redrawn for DC analysis. Step 2: Analysis of Thevenin equivalent network to the left of base terminal

10. Step 2(a): Replaced the voltage sources with short-circuit equivalent and gives the value of R TH

11. Step 2(b): Determining the E TH by replacing the voltage sources and open circuit Thevenin voltage. Then apply the voltage- divider rule.

12. Step 3: The Thevenin network is then redrawn and I BQ can be determined by KVL

13. Book Boyelstad Fixed bias circuit: section 4.3 page 166-168. exmaple 4.1 Load-line analysis: page 150-152,157. example 4.3. Voltage-divider bias: section 4.5 pages 157-160. example 4.7.

14. Homework Problem 5 (a,b,c,d,e,g) and Problem 19 in Chapter 4 Book: Boylestad