laboratorio transstores tbj

1. Electronics II (EECE 3120)
Lab 1 (Alternative Lab)
Version: EECE_3120_2019_Rev_-
Page 1 of 8
Transistor (BJT) Amplifiers
Objective:
o Investigate Bipolar Junction Transistor (BJT) amplifiers
References:
1) Recitation textbook
2) This lab was developed from:
Buchla, D. M. (2008). Laboratory Exercises for Electronic Devices. (8th ed.). Pearson, NJ
Test Equipment Required:
o 1 Breadboard
o 1 Dual Power Supply (+15 V and –15 V)
o 1 Voltmeter
o 1 Bench “Shoebox” containing cables and other test components
Materials (Components)
o 1 100 Ω Resistor
o 1 330 Ω Resistor
o 2 1 k Resistor
o 1 4.7 k Resistor
o 2 10 k Resistor
o 2 1.0 µF Capacitor
o 1 10 µF Capacitor
o 1 47 µF Capacitor
o 1 33 k Resistor
o 1 10 k Potentiometer
o 1 2N3904 npn Transitor (or BJT transistor assigned by the instructor)
o 1 2N3906 pnp Transistor (or BJT transistor assigned by the instructor)
WARNINGS AND PRECAUTIONS
1. Never install or remove components from an energized circuit or equipment
2. Do not construct circuits while energized
3. Follow electrical safety precautions

2. Electronics II (EECE 3120)
Lab 1 (Alternative Lab)
Version: EECE_3120_2019_Rev_-
Page 2 of 8
Background Information
This lab focuses on small-signal amplifiers that produce a replica of the input signal at the output. In
the first part, you will test a common-emitter amplifier and compare your results to the calculated and
simulated values. In a common-emitter (CE) amplifier, the input signal is applied between the base
and emitter, and output signal is developed between the collector and emitter. The transistor's emitter
is common to the input and output circuits, hence, the term common-emitter. We will compute the dc
and ac parameters for a common-emitter (CE) amplifier. Build the amplifier and measure these
parameters.
In the last part of this lab, you will investigate the common-collector (CC) amplifier using a pnp
transistor. The common-collector (CC) amplifier (also called the emitter-follower) has the input signal
applied to the base, and the output signal is taken from the emitter. The ac output voltage almost
perfectly duplicates the input voltage waveform. While this implies that the voltage gain is
approximately 1, the current gain is not; hence, it can deliver increased signal power to a load. The CC
amplifier is characterized by a high input resistance and a low output resistance. We will compute
the dc and ac parameters for a common-collector (CC) amplifier using a pnp transistor and we will also
build the amplifier and measure these parameters.
Pre-Lab Preparation
1. Ability to Log into Blackboard
2. If a “hard” copy of the lab is required, download from Blackboard and print prior to the start of the
lab
3. Read this lab and perform all required reference readings along with constructing the appropriate
tables in your lab notebook
4. Perform all calculations PRIOR TO arriving in the lab
Procedure
1) The Common-Emitter Amplifier:
a. Measure and record the values of the resistors listed in Table 1.
Table 1

3. Electronics II (EECE 3120)
Lab 1 (Alternative Lab)
Version: EECE_3120_2019_Rev_-
Page 3 of 8
Table 2
b. Calculate the dc quantities listed in Table 2 for the CE amplifier in Figure 1. Because
βRE ≥ 10R2, you can use the unloaded voltage-divider analysis method to obtain VB.
Subtract VBE from VB to obtain VE. Compute IE by applying Ohm's law to the resistors in
the emitter circuit. Find VC by subtracting VRC from VCC. Subtract VE from VC to obtain
VCE. Enter your computed values in Table 2.
Figure 1
c. Construct the amplifier shown in Figure 1. The signal generator should be turned off.
Measure and record the dc voltages listed in Table 2.
d. Calculate the four ac parameters listed in the first column of Table 3. The input signal,
Vin, is given as 300 mVpp. This is both Vin and the ac base voltage, Vb.
Multiply Vin by the computed voltage gain to calculate the ac voltage at the collector; this
is both VC and Vout.
e. Turn on the signal generator and set Vin for 300 mVPP at 1.0 kHz with the generator
connected to the circuit. Use the oscilloscope to set the proper voltage and check the
frequency. Measure the ac signal voltage at the transistor's emitter and at the collector.
Note that the signal at the emitter is less than at the base. Use Vin and the ac collector
voltage (Vout) to determine the measured voltage gain, AV. The measurement of Rin(tot)
and βac is explained in step f and g. Record the measured values of Vin, Ve, Vout, and AV in
Table 3.

4. Electronics II (EECE 3120)
Lab 1 (Alternative Lab)
Version: EECE_3120_2019_Rev_-
Page 4 of 8
Table 3
f. The measurement of Rin(tot) is done indirectly because it is an ac resistance that cannot be
measured with an ohmmeter. The output signal (Vout) is measured with an oscilloscope and
recorded with the amplifier operating normally (no clipping or distortion). A rheostat (Rtest)
is then inserted in series with the source as shown in Figure 2. The rheostat is varied
until Vout drops to one-half the value prior to inserting Rtest. With this condition,
Vin = Vtest and Rin(tot) must be equal to Rtest. Rtest can then be removed and measured with
an ohmmeter. Using this method, measure Rin(tot) and record the result in Table 3.
Figure 2
g. You can obtain an estimate of βac from Rin(tot) and the known bias resistor values. Recall
that:
Starting with the parallel resistor formula, you can rearrange it and use it to calculate βac
indirectly. The equation is:
Enter the result as the measured value of βac in Table 3. The result is an approximation of
βac.
h. Troubleshooting: Remove the bypass capacitor, C2, from the circuit, simulating an open
capacitor. Measure the ac signal voltage at the transistor's base, emitter, and collector.

5. Electronics II (EECE 3120)
Lab 1 (Alternative Lab)
Version: EECE_3120_2019_Rev_-
Page 5 of 8
Measure the voltage gain of the amplifier. Record your observations with open C2.
i. Replace C2 and reduce RL to 1.0 kΩ, simulating a change in load conditions.
Observe the ac signal voltage at the transistor's base, emitter, and collector. Record your
observations for smaller load.
j. Replace RL with the original 10 kΩ resistor and open RE1. Measure the dc voltages at the
base, emitter, and collector. Is the transistor in cutoff or in saturation? Explain.
k. Replace RE1 and open R2. Measure the dc voltages at the base, emitter and collector. Is the
transistor in cutoff or saturation? Explain.
l. PRIOR TO DISASSEMBLY, have a TA or the instructor verify proper operation of your
circuit. The TA or Instructor shall initial in your Notebook.
2) The Common-Collector Amplifier:
a. Test a CC amplifier (also called an emitter-follower) constructed with a pnp transistor.
Measure and record the values of the resistors listed in Table 4.
Table 4
Figure 3

6. Electronics II (EECE 3120)
Lab 1 (Alternative Lab)
Version: EECE_3120_2019_Rev_-
Page 6 of 8
b. Compute the dc quantities listed in Table 5 for the CC amplifier shown in Figure 3.
Remember that the emitter voltage is 0.7 V larger than VB for the pnp transistor. Enter
your computed dc quantities in Table 5.
Table 5
Table 6
c. Construct the amplifier shown in Figure 3.
The signal generator should be turned off. With the power supply on, measure and
record the dc voltages listed in Table 5. Your measured and computed values should agree
within 10%.
d. Compute and record the ac quantities listed in Table 6. For computing the emitter
resistance, assume Vb is the same as the source voltage, VS. If you do not know the βac for
your transistor, you can still obtain reasonable results if you assume it is 100.
e. Turn on the signal generator and set VS for 1.0 Vpp at 1.0 kHz. Use the oscilloscope to set
the proper voltage and check the frequency.
Measure the input ac signal voltage at the base, Vb, and the output signal voltage at the
emitter, Ve, to determine the voltage gain, AV. Measure Rin(tot) using the method
employed for the CE amplifier described in Part 1 (step f).
To calculate power, substitute the measured Rin(tot) and measured RL value into the
power formula V2/R (use rms voltages to calculate power). Record the measured ac
parameters in Table 6.
f. With a two-channel oscilloscope, compare the input and output waveforms. What is the
phase relationship between Vin and Vout?
g. Troubleshooting: Table 7 lists some possible troubles with the CC amplifier. For each
trouble listed, predict the effect on the dc voltages. Then insert the trouble into the circuit
and test your prediction. Insert the open collector and open emitter troubles by removing
the transistor lead and measuring the voltages at the circuit. For each fault, describe the
effect on the ac output waveform (clipped, no output, etc.).

7. Electronics II (EECE 3120)
Lab 1 (Alternative Lab)
Version: EECE_3120_2019_Rev_-
Page 7 of 8
Table 7
h. Replace RL with a 10 kΩ variable resistor set to 1.0 kΩ. Connect an oscilloscope probe to
the emitter. Increase the signal until you just begin to observe clipping. If the positive
peaks are clipped, you are observing cutoff clipping because the transistor is turned off. If
the negative peaks are clipped, this is called saturation clipping because the transistor is
fully conducting. What type of clipping is first observed?
i. Vary RL while observing the output waveform. Describe your observations.
j. PRIOR TO DISASSEMBLY, have a TA or the instructor verify proper operation of your
circuit. The TA or Instructor shall initial in your Notebook.
SUMMARY:
We have had our first look at BJT amplifiers as well as some of the common problems that we may encounter
with these circuits.
Lab Notebook Requirements:
1) Ensure that you have recorded all the data requested during the lab in your lab notebook as well
as your lab report.
Lab Report:
1) Use the course required format.
Lab Questions:
Questions related to Part 1
1) In Part 1, step f, you were instructed to measure the input resistance while monitoring the output
voltage. Why is this procedure better than monitoring the base voltage?
2) Does the load resistor have any effect on the input resistance? Explain your answer.
3) What is the purpose of the unbypassed emitter resistor RE1? What design advantage does it offer?
4) When the bypass capacitor, C2, is open, you found that the gain is affected. Explain why.

8. Electronics II (EECE 3120)
Lab 1 (Alternative Lab)
Version: EECE_3120_2019_Rev_-
Page 8 of 8
Questions related to Part 2
1) In Part 2, step h, you observed the effect of clipping due to saturation or cutoff of the transistor.
The statement was made that if the positive peaks are clipped, you are observing cutoff clipping
because the transistor is turned off. Is this statement true if the CC circuit had been constructed
with an npn transistor? Why or why not?
2) Common-collector amplifiers have a voltage gain less than 1 but still provide power gain. Explain
why.