OBJECTIVES

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

2. To theoretically calculate and verify the circuit using Ohm's law or Kirchhoff's law, which were learned in previous classes.

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

1. Determine if the collector-based junction is forward or reversed biased.

   II.      PARTS / Equipment List:

   Equipment:

IBM PC or compatible                             

DMM (digital multimeter)

         Variable dc power supply

Parts:    

6- 10 k? resistor

1 - 2N3904 Transistor                                          

Wire and wire stripper                             

Software:

MultiSim 11

PROCEDURE

1. Theoretical analysis of the Circuit

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

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

1. 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.

1.  

   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. Multisim Simulation and Circuit Calculations

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

2. 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.

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 (V_RC) 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.2 above. 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 +V_cc?

2. How much current is passing through the emitter resistor in mA?

3. What is the voltage drop across the collector load resistance (V_RC) 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:  

1. What is the total resistance between the base and +V_cc?

2. How is passing through the emitter resistor in mA?

3. What is the voltage drop across the collector load resistance (V_RC) in V?

4. What is the collector current in mA? Approximate.

1. Construction of the BJT Biasing Circuit on a proto board and Measurement of Circuit Characteristics

1. Construct the circuit in Fig 1. 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 V_cc?

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 (V_RC) 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 +V_cc?

2. Is the base-to-emitter voltage close to 0.7 V?

3. Is the collector-to-emitter voltage less than V_cc?

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 (V_RC) in V?

7. What is the collector current in mA? Approximate.

8. By removing R₂ and therefore changing the value of the base-to-V_CC resistance. Has it changed the collector-to-emitter voltage? How?

9. By removing R₂ and therefore changing the value of the base-to-V_CC resistance. Has it changed the collector current? How?

10. By removing R₂ and therefore changing the value of the base-to-V_CC resistance. Has it changed the base-to-emitter voltage? By how much?

11. By removing R₂ and therefore changing the value of the base-to-V_CC resistance. 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.

2. Answer the following questions on the worksheet:

1. What is the total resistance between the base and +V_cc?

2. Is the base-to-emitter voltage close to 0.7 V?

3. Is the collector-to-emitter voltage less than V_cc?

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 (V_RC) in V?

7. What is the collector current in mA? Approximately.

8. By removing R₄ and therefore changing the value of the base-to-V_CC resistance. Has it changed the collector-to-emitter voltage? How?

9. By removing R₄ and therefore changing the value of the base-to-V_CC resistance. Has it changed the collector current? How?

10. By removing R₄ and therefore changing the value of the base-to-V_CC resistance. Has it changed the base-to-emitter voltage? By how much?

11. By removing R₄ and therefore changing the value of the base-to-V_CC resistance. Has it changed the emitter current? How?

12. Is the transistor operating in cutoff, linear, or saturation region?

     

IV.    SUMMARY

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

a)   Did your theoretical calculations closely match the results obtained from the Multisim simulation? (Yes/ No)  

      Comments:

b)   Did your theoretical calculations closely match the results obtained from the Proto Board circuit? (Yes/ No)

      Comments:

c)   Did your results obtained from the Multisim simulation closely match the results obtained from the Proto Board circuit? (Yes/ No)

    Comments: