Tutorial 2 BJTs, Transistor Bias Circuits, BJT Amplifiers FETs and FETs Amplifiers. Part 1: BJTs, Transistor Bias Circuits and BJT Amplifiers

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1 Tutorial 2 BJTs, Transistor Bias Circuits, BJT Amplifiers FETs and FETs Amplifiers Part 1: BJTs, Transistor Bias Circuits and BJT Amplifiers 1. Explain the purpose of a thin, lightly doped base region. 2. Why is the base current in a transistor so much less than the collector current? 3. Given I E = 5.34 ma and I B = 475 µa. Calculate the value of I C. 4. Given I C = 5.35 ma and I B = 50 µa. Calculate α DC. 5. Calculate each current in Figure 1 and the value of β DC. Figure 1 6. Calculate V CE, V BE and V CB for both circuits in Figure 2. Figure 2 7. Determine whether or not the transistors in Figure 2 above are saturated. 8. A certain transistor is to be operated at a collector current of 50 ma. How high can V CE reach without exceeding a P D(max) of 1.2 W. 9. A 50 mv signal is applied to the base of a properly biased transistor with r e = 10 Ω and R C = 560 Ω. Calculate the signal voltage at the collector. 1

2 10. The transistor in Figure 3 has a β DC = 50. Calculate the value of R B required to ensure the saturation when V IN = 5 V. What value of V IN be to cutoff the transistor? Assume V CE(sat) = 0 V. VCC +15 V 1.2 kω Figure Calculate the value of the β DC of the transistor shown in Figure 4. Figure Refer to the transistor data sheet in appendix; calculate whether or not the transistor is saturated in circuit as shown in Figure 5 based on the maximum specified value of h FE. Figure 5 2

3 13. Calculate the Q-point for a biased transistor as shown in Figure 6. Given I B = 150 µa and β DC = kω V CC 18 V Figure Determine whether the transistor in Figure 7 is biased in cutoff, saturation or the linear region. Keep in mind that I C = β DC I B is valid only in the linear region. Figure Calculate all transistor terminal voltages with respect to ground in Figure 8. Do not neglect the input resistance at the base or V BE. Figure 8 3

4 16. Consider circuit as shown in Figure 9 (a) Analyze the circuit to determine the correct voltages at the transistor terminals with respect to ground. Assume β DC = 100. (b) To what value can R E be reduced without the transistor going into saturation? (c) Taking V BE into account, how much will I E change with temperature increase from 25 o C to 100 o C? The V BE = 0.7 V at 25 o C and decrease 2.5 mv per degree Celcius. Neglect β DC. Figure A collector-feedback circuit uses an npn transistor. Given V CC = 12 V, R C = 1.2 kω and R B = 47 kω. Sketch the circuit and calculate the collector current and the collector voltage if β DC = A certain transistor has a dc beta (h FE ) of 130. Given I B = 10 µa and α DC = 0.99, calculate r e. 19. Sketch the dc equivalent circuit and the ac equivalent circuit for the unloaded amplifier in Figure 10. Figure 10 4

5 20. Refer to the amplifiers circuit in Figure 11, calculate the following dc values: (a) V B (b) V E (c) I E (d) I C (e) V C (f) V CE 10 kω Figure From Problem 20 above, calculate the following ac values: (a) R in(base) (b) R in (c) A v (d) A i (e) A p 22. Refer to the unloaded emitter-follower circuit as shown in Figure 12 (a) Calculate the exact voltage gain (b) Calculate the total input resistance (c) Calculate the dc output voltage Figure 12 5

6 23. Calculate R in(emitter), A v, A i and A p for the unloaded amplifier in Figure 13. Figure Match the following generalized characteristics with the appropriate amplifier configuration. (a) Unity current gain, good voltage gainm very low input resistance (b) Good current gain, good voltage gain, low input resistance (c) Good current gain, unity voltage gain, high input resistance 25. Figure 14 shows the two stage, capacitively coupled amplifier circuit. Calculate the following values: (a) Voltage gain of each stage (b) Overall voltage gain (c) Express the gains in (a) and (b) in db Figure Express the following voltage gains in db: (a) 12 (b) Express the following voltage gains in db as standard voltage gains: (a) 6 (b) 40 6

7 Appendix Partial transistor data sheet 7