Page 1 of 5
Name: ______________________________
ECET 242 – Electronic Circuits
Lab 6
Transistor Amplifiers
Objective:
Students successfully completing this lab exercise will accomplish the following
objectives:
1. Learn to construct a common-emitter amplifier circuit.
2. Analyze the amplifier circuit and conduct measurements to determine AC
operating parameters.
Lab Report:
An informal lab report will be required for this lab. Include all collected data,
typed responses to any discussion questions, and graphs generated using a
computer-based application. The report will be due 1 week after the lab exercise
is carried out.
Equipment:
Dual DC power supply
2N3904 NPN transistor
Resistors: 10 Ω, 470 Ω, 680 Ω, 680 Ω, 3 k Ω, and 2.2 k Ω
Polarized capacitors: 100µF, 100µF and 22µF
Breadboard
Wire Jumper Kit
Connecting leads
Oscilloscope
Digital Multimeter (DMM)
Procedure 1: DC Measurements and Analysis
1.
Select the resistor values shown in Table 1. Measure and record the actual values of each
resistor in Table 1 also.
Table 1: Measured Values of Amplifier Biasing Resistors
Component
RC = 680 Ω
RL = 680 Ω
RE =470 Ω
R1 = 3 k Ω
R2 = 2.2 k Ω
Measured Value
Page 2 of 5
2.
Construct the universal biasing circuit shown in Figure 1. Use the resistors selected in the
previous step. Select capacitors as follows: CIN = 22 µF, COUT = CE = 100 µF.
VCC
R1
RC
COUT
VC
CIN
RL
VB
VE
R2
RE
CE
Figure 1: Common Emitter Amplifier Circuit
3.
Turn on the power supply and set the voltage to 20 V. Measure the transistor DC voltages
and record your results below.
VB = ____________
VC = ____________
VE = ____________
VC should be about 10 V. If it is not, then debug the circuit.
Using Ohm’s Law the measured voltages above, and the measured resistances in step 2,
calculate the collector and emitter currents:
IC = ____________ IE = ____________
Using the relation, IE = IC + IB, substitute the calculated currents above and calculate the
base current:
IB = ____________
4.
Pull out the transistor and measure the voltage at the base test point.
VB with transistor removed = ____________
Calculate the percent change in VB between no transistor and transistor in.
% change = _____________
5.
Have the instructor check your circuit.
Page 3 of 5
Procedure 2: AC Measurements and Analysis
6.
Connect the audio generator to an AC voltmeter. Set the frequency to 1000 Hz. Adjust the
attenuation for an AC voltage of 30 mV rms.
7.
Insert the transistor back into the circuit. Connect a 10 Ω resistor in series with the audio
generator in series with CIN. Measure the AC voltages vHI and vLOW on each side of the 10
Ω resistor. Use Ohm’s Law to calculate the input current, iIN, and the input impedance, ZIN.
8.
vHI = ____________ mV rms
vLOW = vIN = ____________ mV rms
iIN = ____________ µA rms
ZIN = ____________ kΩ
From the current divider rule, iR1 || R2 = iIN x ZIN / (R1 || R2), calculate the AC current in the (R1
|| R2) parallel combination.
iR1 || R2 = ____________ µA rms
9.
From Kirchhoff’s Current Law, iIN = ib + iR1 || R2, calculate the AC base current.
ib = ____________ µA rms
10.
From Ohm’s Law, vIN = ib x ZIN (base),calculate the AC impedance looking into the base
current.
ZIN (base) = ____________ Ω
11.
Use the DMM to measure the AC output voltage, vOUT, on the high side of the load resistor,
RL. The high side is connected to the capacitor, COUT. Calculate the AC output current,
iOUT, from Ohm’s Law.
vOUT = ____________ mV rms
12.
iOUT = ____________ mA rms
From Ohm’s Law, vOUT = iRCRC, calculate the AC current in the collector resistor.
iRC = ____________ mA rms
13.
From Kirchhoff’s Current Law, iC = iRC + iOUT, calculate the AC collector current.
ic = ____________ mA rms
14.
Calculate the AC current gain of the transistor:
hfe = ic / ib = ____________
15.
From the measurements above, calculate the voltage gain, Av = vOUT / vIN, and the current
gain, Ai = iOUT / iIN and the power gain, AP = Av x Ai. Record all results from these
calculations and those above in Table 2 below.
16.
Attach the channel 1 probe of the oscilloscope to the test point for vIN and attach the
channel 2 probe of the oscilloscope to the test point for vOUT. Set up the oscilloscope to
display channels 1 and 2.
17.
Sketch vIN versus time and vOUT versus time on the same graph. On the left vertical axis of
the sketch, indicate input voltage values at each major grid line. On the right vertical axis,
indicate output voltage values at each major grid line. On the horizontal axis, indicate time
values at each major grid line.
Page 4 of 5
Figure 2: Input voltage (vIN) and outputvoltage (vOUT) versus time
18.
Using no measurements and only nominal component values, calculate the transistor
voltages and currents for hfe = 150. Show calculations on the next page. Record your
calculated values in column 2 of Table 2.
Table 2: Measured versus Calculated Parameters for a Common Emitter Amplifier
Measured or Calculated
from Measured Values
Parameter
Symbol
DC
Base Voltage
Calculated
Units
VB
V
DC
Collector Voltage
VC
V
DC
Emitter Voltage
VE
V
DC
Base Current
IB
mA
DC
Collector Current
IC
mA
DC
Emitter Current
IE
mA
AC Impedence
Looking into Base
ZIN(Base)
Ω
AC
Input Impedence
ZIN
Ω
AC
Input Current
iIN
µA
AC
Base Current
ib
µA
AC
Collector current
ic
mA
AC Current Gain
of the Transistor
hfe
AC
Output Current
iOUT
mA
rms
AC
Output Voltage
vOUT
V
rms
Amplifier
Voltage Gain
Av
Amplifier
Current Gain
Ai
Amplifier Power
Gain
AP
Page 5 of 5
Calculations: