18.4.1: DC Load Line
1. Consider the circuit of Figure 18.3.1 using Vcc = 10 volts, R1 = 10 k\(\Omega\), R2 = 3.3 k\(\Omega\), Re = 4.7 k\(\Omega\) and Rc = 5.6 k\(\Omega\). Using the approximation of a lightly loaded “stiff” voltage divider, determine the ideal end points of the DC load line and the Q point, and record these in Table 18.5.1.
18.4.2: Circuit Voltages and Beta
2. Continuing with the component values indicated in step one, compute the theoretical base, emitter and collector voltages, and record them in Table 18.5.2 (Theory).
3. Build the circuit of Figure 18.3.1 using Vcc = 10 volts, R1 = 10 k\(\Omega\), R2 = 3.3 k\(\Omega\), Re = 4.7 k\(\Omega\) and Rc = 5.6 k\(\Omega\). Measure the base, emitter and collector voltages and record them in the first row of Table 18.5.2 (Experimental). Compute the deviations between theoretical and experimental and record these in the first row of Table 18.5.2 (% Deviation).
4. Measure the base and collector currents and record these in the first row of Table 18.5.3. Based on these, compute and record the experimental beta as well.
5. Swap the transistor with the second transistor and repeat steps 3 and 4 using the second rows of the tables.
6. Swap the transistor with the third transistor and repeat steps 3 and 4 using the third rows of the tables.
7. The collector current of the circuit can be altered by a variety of means including changing the emitter resistance. If the base voltage is held constant, the collector current is determined by the emitter resistance via Ohm’s law. Redesign the circuit to achieve half of the quiescent collector current recorded in Table 18.5.1. Obtain a resistor close to this value, swap out the original emitter resistor and measure the resulting current. Record the appropriate values in Table 18.5.4.
8. Return the original emitter resistor to the circuit. Consider each of the individual faults listed in Table 18.5.5 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 18.5.5.
18.4.5: Computer Simulation
9. Build the circuit of Figure 18.3.1 in a simulator. Run a DC simulation and record the resulting transistor voltages in Table 18.5.6.