17.4: Procedure

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17.4.1: DC Load Line

11. Consider the circuit of Figure 17.3.1 using Vcc = 15 volts, Vee = −12 volts, Rb = 33 k\(\Omega\), Re = 22 k\(\Omega\) and Rc = 15 k\(\Omega\). Using the approximation of a negligible base voltage, determine the ideal end points of the DC load line and the Q point, and record these in Table 17.5.1.

17.4.2: Circuit Voltages and Beta

12. Continuing with the component values indicated in step one, compute the theoretical emitter and collector voltages, and record them in Table 17.5.2 (Theory). For the theoretical base voltage entry, assume a beta of approximately 150 and determine the base current and voltage from the theoretical collector current recorded in the Table 17.5.1.

13. Build the circuit of Figure 17.3.1 using Vcc = 15 volts, Vee = −12 volts, Rb = 33 k\(\Omega\), Re = 22 k\(\Omega\) and Rc = 15 k\(\Omega\). Measure the base, emitter and collector voltages and record them in the first row of Table 17.5.2 (Experimental). Compute the deviations between theoretical and experimental and record these in the first row of Table 17.5.2 (% Deviation).

14. Measure the base and collector currents and record these in the first row of Table 17.5.3. Based on these, compute and record the experimental beta as well.

15. Swap the transistor with the second transistor and repeat steps 3 and 4 using the second rows of the tables.

16. Swap the transistor with the third transistor and repeat steps 3 and 4 using the third rows of the tables.

17.4.3: Design

17. The collector voltage of the circuit can be altered by a variety of means including changing the collector resistance. If the emitter supply and resistance are held constant, the collector voltage is determined by the collector resistance and the collector supply. Redesign the circuit to achieve a collector voltage of approximately 10 volts. Obtain a resistor close to this value, swap out the original collector resistor and measure the resulting voltage. Record the appropriate values in Table 17.5.4.

17.4.4: Troubleshooting

18. Return the original collector resistor to the circuit. Consider each of the individual faults listed in Table 17.5.5 and estimate the resulting base, emitter and collector voltages. Introduce each of the individual faults in turn and measure and record the transistor voltages in Table 17.5.5.

17.4.5: Computer Simulation

19. Build the circuit of Figure 17.3.1 in a simulator. Run a DC simulation and record the resulting transistor voltages in Table 17.5.6.