# ECET 220 Week 2 Lab Answers ( graded )

ECET 220 Week 2 Lab Answers ( graded )

Week 2 Lab Instructions

Bipolar Junction Transistor – Biasing

1. Objectives

• To analyze a normally biased BJT circuit comprising of a BJT and resistors and measure the circuit voltages between emitter, common, base, and collector.

• To theoretically calculate and verify the circuit using Ohm’s Law, KCL and KVL.

• Determine the voltage drop across the collector load resistance and measure the current passing through the emitter and collector resistors.

1. Equipment and Parts List

Equipment:

• IBM PC or compatible
• DMM (digital multimeter)
• Variable dc power supply

Parts:

 Qty. Component Tolerance Band Wattage Rating, W 1 2N3904 Transistor 6 10 K Ω  Resistor gold ¼ 1 Proto Board Hookup wires of different colors

Software: MultiSim

III. Procedure

1. Theoretical Analysis

1. Given the circuit in Figure 1, calculate the total resistance between the base and VCC in kΩ and the total collector resistance (combination of R3 and R4) in kΩ. Enter the values obtained in Table 1 on the worksheet.

Figure 1

1. Given Figure 1, calculate the circuit voltages cited below entering the values in Table 2 on the worksheet.

 Voltages VCC Emitter to common Base to common Collector to common Base to emitter Collector to emitter

1. If resistor R2 is removed from the base circuit, calculate the circuit resistances and voltages cited below and enter the values in Tables 3 and 4 respectively on the worksheet.

 Resistances (KΩ) Base and +VCC Total Collector Resistance

 Voltages (V) VCC Emitter to common Base to common Collector to common Base to emitter Collector to emitter

1. Put resistor R2 back in the circuit and remove R4 from the collector circuit.Calculate the circuit resistances and circuit voltages cited in part A.3 above and enter the calculated values in Tables 5 and 6 respectively on the worksheet.

1. B. MultiSim Simulation Results

1. Launch the Multisim Simulator and build the circuit schematic shown in Figure 1.Note that you will need a Digital Multimeter to measure the output voltages.

1. Set the DC source voltage to 9V. Consider the negative side of the source as common, and measure the circuit voltages cited below. Enter measured values in Table 7 on the worksheet.

 Measured Voltages VCC Emitter to common Base to common Collector to common Base to emitter Collector to emitter

1. Answer the following questions on the worksheet.

1. How much current is passing through the emitter resistor in mA?
2. What is the voltage drop across the collector load resistance (VRC) in V?
3. What, approximately, is the collector current in mA?

1. Remove resistor R2 from the base circuit and measure the circuit voltages cited in part B.2above.Enter measured values in Table 8 on the worksheet.

1. Answer the following questions on the worksheet.

1. What is the total resistance between the base and +Vcc?
2. How much current is passing through the emitter resistor in mA?
3. What is the voltage drop across the collector load resistance (VRC) in V?
4. What, approximately, is the collector current in mA?

1. Replace resistor R2 as shown in Figure 1 and remove resistor R4 from the collector circuit. Measure the circuit voltages cited in part B.2 above and enter the values in Table 9 on the worksheet.

1. Answer the following questions on the worksheet.
2. What is the total resistance between the base and +Vcc?
3. How is passing through the emitter resistor in mA?
4. What is the voltage drop across the collector load resistance (VRC) in V?
5. What is the collector current in mA? Approximate.

1. Experimental Breadboard Results

1. Construct the circuit in Figure1.(For online students: Take a picture of your circuit and place it on the worksheet.)
2. Set the DMM to measure the output voltages at different points in the circuit.
3. Set the DC source voltage to 9V. Consider the negative side of the source as common, and measure the circuit voltages cited in part B.2. Enter measured values in Table 10.

1. Answer the following questions on the worksheet.

1. Is the base positive or negative with respect to the emitter?
2. Is the base-to-emitter voltage close to 0.7 V?
3. Is the collector-to-emitter voltage less than Vcc?
4. Is the collector-to-emitter voltage greater than 0.3 V?
5. How much current must be passing through the emitter resistor in mA?
6. What is the voltage drop across the collector load resistance (VRC) in V?
7. What is the collector current in mA? Approximate.
8. Is the collector more positive or negative than the base?
9. Is the collector-base junction forward or reverse biased?
10. Is the transistor operating in cutoff, linear or saturation region?

1. Remove resistor R2 from the base circuit and measure the circuit voltages cited in part B.2 above. Enter measured values in Table 11 on the worksheet.

1. Answer the following questions on the worksheet.

1. What is the total resistance between the base and +Vcc?
2. Is the base-to-emitter voltage close to 0.7 V?
3. Is the collector-to-emitter voltage less than Vcc?
4. Is the collector-to-emitter voltage greater than 0.3 V?
5. How much current must be passing through the emitter resistor in mA?
6. What is the voltage drop across the collector load resistance (VRC) in V?
7. What is the collector current in mA? Approximate.
8. By removing R2 and therefore changing the value of the base-to-VCC Has it changed the collector-to-emitter voltage? How?
9. By removing R2 and therefore changing the value of the base-to-VCC Has it changed the collector current? How?
10. By removing R2 and therefore changing the value of the base-to-VCC Has it changed the base-to-emitter voltage? By how much?
11. By removing R2 and therefore changing the value of the base-to-VCC Has it changed the emitter current? How?
12. Is the transistor operating in cutoff, linear, or saturation region?

1. Replace resistor R2 as shown in Figure 1 and remove resistor R4 from the collector circuit. Measure the circuit voltages cited in part B.2 above. Enter measured values in Table 12 on the worksheet.

1. Answer the following questions on the worksheet.

1. What is the total resistance between the base and +Vcc?
2. Is the base-to-emitter voltage close to 0.7 V?
3. Is the collector-to-emitter voltage less than Vcc?
4. Is the collector-to-emitter voltage greater than 0.3 V?
5. How much current must be passing through the emitter resistor in mA?
6. What is the voltage drop across the collector load resistance (VRC) in V?
7. What is the collector current in mA? Approximately.
8. By removing R4 and therefore changing the value of the base-to-VCC Has it changed the collector-to-emitter voltage? How?
9. By removing R4 and therefore changing the value of the base-to-VCC Has it changed the collector current? How?
10. By removing R4 and therefore changing the value of the base-to-VCC Has it changed the base-to-emitter voltage? By how much?
11. By removing R4 and therefore changing the value of the base-to-VCC Has it changed the emitter current? How?
12. Is the transistor operating in cutoff, linear, or saturation region?

1. Results Analysis

1. Complete the table containing the Theoretical, Simulation, and Experimental results obtained for the input and output signals.

1. Compare the theoretical, simulation, and hardware circuit results, and enter your comments on the worksheet.

1. Troubleshooting

Describe any problems encountered and how those problems were solved.

1. Questions

Please provide the answer to the following questions on the worksheet.

1. Did your theoretical calculations closely match the results obtained from the constructed circuit?

(Yes, No)_____

1. Compare the results obtained from the Figure 1 circuit with the Figure 1 circuit with the removal of R2. Explain changes in the base, collector, emitter, base-to-emitter, and collector-to-emitter voltages. Also, explain changes in the base, collector and emitter currents.Comments:

1. Compare the results obtained from the Figure 1 circuit with the Figure 1 circuit with the removal of R4. Explain changes in the base, collector, emitter, base-to-emitter, and collector-to-emitter voltages. Also, explain changes in the base, collector and emitter currents.Comments:

1. What affect does the base biasing have on the DC circuit operating point (Q point)?Comments:

1. What affect does the collector resistor have on the DC circuit operating point (Q point)?Comments: