ECET 220 Week 2 Lab Answers ( graded
)
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Week 2 Lab Instructions
Bipolar Junction Transistor –
Biasing
- 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.
- Equipment and Parts List
Equipment:
- IBM PC or compatible
- DMM (digital multimeter)
- Variable dc power supply
Parts:
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Qty.
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Component
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Tolerance Band
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Wattage Rating, W
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1
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2N3904 Transistor
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|||
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6
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10 K Ω Resistor
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gold
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¼
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1
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Proto Board
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|||
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Hookup wires of different colors
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Software: MultiSim
III. Procedure
- Theoretical Analysis
- 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
- Given Figure 1, calculate the circuit voltages cited
below entering the values in Table 2 on the worksheet.
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Voltages
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VCC
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Emitter to common
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Base to common
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Collector to common
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Base to emitter
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Collector to emitter
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- 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.
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Resistances (KΩ)
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Base and +VCC
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Total Collector Resistance
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Voltages (V)
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VCC
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Emitter to common
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Base to common
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Collector to common
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Base to emitter
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Collector to emitter
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- 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.
- B. MultiSim Simulation Results
- 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.
- 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.
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Measured Voltages
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VCC
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Emitter to common
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Base to common
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Collector to common
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Base to emitter
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Collector to emitter
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- Answer the following questions on the worksheet.
- How much current is passing through the emitter
resistor in mA?
- What is the voltage drop across the collector load
resistance (VRC) in V?
- What, approximately, is the collector current in mA?
- 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.
- Answer the following questions on the worksheet.
- What is the total resistance between the base and +Vcc?
- How much current is passing through the emitter
resistor in mA?
- What is the voltage drop across the collector load
resistance (VRC) in V?
- What, approximately, is the collector current in mA?
- 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.
- Answer the following questions on the worksheet.
- What is the total resistance between the base and +Vcc?
- How is passing through the emitter resistor in mA?
- What is the voltage drop across the collector load
resistance (VRC) in V?
- What is the collector current in mA? Approximate.
- Experimental Breadboard Results
- Construct the circuit in Figure1.(For online
students: Take a picture of your circuit and place it on the worksheet.)
- Set the DMM to measure the output voltages at different
points in the circuit.
- 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.
- Answer the following questions on the worksheet.
- Is the base positive or negative with respect to the
emitter?
- Is the base-to-emitter voltage close to 0.7 V?
- Is the collector-to-emitter voltage less than Vcc?
- Is the collector-to-emitter voltage greater than 0.3 V?
- How much current must be passing through the emitter
resistor in mA?
- What is the voltage drop across the collector load
resistance (VRC) in V?
- What is the collector current in mA? Approximate.
- Is the collector more positive or negative than the
base?
- Is the collector-base junction forward or reverse
biased?
- Is the transistor operating in cutoff, linear or
saturation region?
- 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.
- Answer the following questions on the worksheet.
- What is the total resistance between the base and +Vcc?
- Is the base-to-emitter voltage close to 0.7 V?
- Is the collector-to-emitter voltage less than Vcc?
- Is the collector-to-emitter voltage greater than 0.3 V?
- How much current must be passing through the emitter
resistor in mA?
- What is the voltage drop across the collector load
resistance (VRC) in V?
- What is the collector current in mA? Approximate.
- By removing R2 and therefore changing the
value of the base-to-VCC Has it changed the
collector-to-emitter voltage? How?
- By removing R2 and therefore changing the
value of the base-to-VCC Has it changed the collector current?
How?
- By removing R2 and therefore changing the
value of the base-to-VCC Has it changed the base-to-emitter
voltage? By how much?
- By removing R2 and therefore changing the
value of the base-to-VCC Has it changed the emitter current?
How?
- Is the transistor operating in cutoff, linear, or
saturation region?
- 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.
- Answer the following questions on the worksheet.
- What is the total resistance between the base and +Vcc?
- Is the base-to-emitter voltage close to 0.7 V?
- Is the collector-to-emitter voltage less than Vcc?
- Is the collector-to-emitter voltage greater than 0.3 V?
- How much current must be passing through the emitter
resistor in mA?
- What is the voltage drop across the collector load
resistance (VRC) in V?
- What is the collector current in mA? Approximately.
- By removing R4 and therefore changing the
value of the base-to-VCC Has it changed the
collector-to-emitter voltage? How?
- By removing R4 and therefore changing the
value of the base-to-VCC Has it changed the collector current?
How?
- By removing R4 and therefore changing the
value of the base-to-VCC Has it changed the base-to-emitter voltage?
By how much?
- By removing R4 and therefore changing the
value of the base-to-VCC Has it changed the emitter current?
How?
- Is the transistor operating in cutoff, linear, or
saturation region?
- Results Analysis
- Complete the table containing the Theoretical,
Simulation, and Experimental results obtained for the input and output
signals.
- Compare the theoretical, simulation, and hardware
circuit results, and enter your comments on the worksheet.
- Troubleshooting
Describe any problems encountered
and how those problems were solved.
- Questions
Please provide the answer to the
following questions on the worksheet.
- Did your theoretical calculations closely match the
results obtained from the constructed circuit?
(Yes, No)_____
Comments:
- 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:
- 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:
- What affect does the base biasing have on the DC
circuit operating point (Q point)?Comments:
- What affect does the collector resistor have on the DC
circuit operating point (Q point)?Comments:
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