SCHOOL OF ENGINEERING AND APPLIED SCIENCE
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
ECE 2115: ENGINEERING ELECTRONICS LABORATORY
Experiment #5:
Characterization of an NPN Bipolar Junction Transistor (BJT)
COMPONENTS
Type
Resistor
Resistor
Transistor
Value
1kΩ
100kΩ
2N3904
Symbol Name
RB
RC
Q1
Multisim Part
Basic/Resistor
Basic/Resistor
Transistors/BJT_NPN/2N3904
Description
----NPN BJT
Table 1 – Component List
OBJECTIVES




To characterize a BJT using the Tektronix Model 571 Curve Tracer
To characterize the base-emitter pn-junction (BEJ) and base-collector pn-junction (BCJ) of a BJT
using the Tektronix Model 571 Curve Tracer
To characterize a BJT using a DC power supply and DMM
To compare measured characterization results to manufacturer specifications
Copyright © 2015 GWU SEAS ECE Department
ECE 2115: Engineering Electronics
1
SEAS
Experiment #5: Characterization of an NPN Bipolar Junction Transistor (BJT)
PRELAB
Part I – Generate Equipment List
1. Read through the lab manual and generate an equipment list.
Part II – Parametric Sweep Simulation of a BJT
Q1
2N3904
VB
VCE
0V
IB
0uA
Figure P.1 – BJT Test Circuit
1. Build and simulate the circuit in Figure P.1 using Multisim.
a. Use the “Parametric Sweep Simulation of a BJT” tutorial on the lab website to
generate an I-V curve (IC vs. VCE) for the 2N3904 BJT.
b. Sweep VCE from 0V to 10V in 0.2V increments.
c. Sweep IB from 10µA to 50µA in 20µA increments.
d. Plot the collector current to generate three different I-V curves.
e. Place markers at VCE = 2V on each curve.
f. Record the values for VCE, IC, and IB from the markers in Table P.1.
g. Re-run the simulation, plotting the voltage at node VB instead of the collector current and
again place markers at VCE = 2V.
h. Record the values for VBE from the markers in Table P.1.
IB
10µA
30µA
50µA
Value
IB
Calculated
Simulated
Measured
VCE
IC
VBE
β
IB
VCE
IC
VBE
β
IB
VCE
IC
VBE
β
Table P.1 – BJT Values
Copyright © 2015 GWU SEAS ECE Department
ECE 2115: Engineering Electronics
2
SEAS
Experiment #5: Characterization of an NPN Bipolar Junction Transistor (BJT)
Part III – BJT Calculations
1. Use Equation P.1 to calculate IC, and record the values in the calculated section of Table P.1.
a. Calculate IC for each value of VBE collected in the simulations in Part II.
b. Assume IS = 6.734fA and the typical value for VT = 26mV (thermal voltage).
c. Calculate the value of the DC current gain (β = IC / IB) for each value of IB in Table P.1.
𝑉𝐵𝐸
𝐼𝐶 ≅ 𝐼𝑆 (𝑒 𝑉𝑇 )
Equation P.1 – Collector Current of NPN BJT in the Active Region of Operation
(Assumes VA >> VCE and n = 1)
Part IV – Specification Sheet Values
1. In the simulation above, we have swept VCE from 0V to 10V and IB from 10µA to 50µA. However,
the 2N3904 BJT can handle a significantly higher set of values.
a. From the specification sheet for the 2N3904 BJT, gather the following specifications:
Parameter
Value
Maximum Collector-Emitter Voltage (VCEO)
Maximum Emitter-Base Voltage (VEBO)
Maximum Continuous Collector Current (IC)
Maximum Collector-Base Voltage (VCBO)
Maximum DC Current Gain (β or hFE)
Base-Emitter ON Voltage (VBE) when VCE=5V
and IC=10mA at room temperature
Table P.2 – 2N3904 BJT Spec Sheet Values
Copyright © 2015 GWU SEAS ECE Department
ECE 2115: Engineering Electronics
3
SEAS
Experiment #5: Characterization of an NPN Bipolar Junction Transistor (BJT)
LAB
Part I – Transistor Characterization Using a Curve Tracer
1. Generate an IC vs. VCE I-V curve for the 2N3904 BJT using the curve tracer.
a. Set the Tektronix Model 571 Curve Tracer to generate three I-V curves for the transistor
with the following limits:
i. Limit IC to be no greater than 10mA.
ii. Set VCE to be swept from 0V to 10V.
iii. Step IB from 10µA to 50µA in 20µA steps to generate three curves.
iv. Save a picture of the resulting family of curves and include in your lab report.
2. Generate an I-V curve for the BEJ and CEJ for the BJT pn-junctions.
a. Set the Tektronix Model 571 Curve Tracer to generate the forward I-V characteristic
curve for the Base-Emitter Junction of the 2N3904 transistor.
i. Determine the limits for the B-E junction using the manufacturer specifications
sheet.
ii. Save a picture of the resulting curve, being sure to note the voltage and current
limits selected.
b. Set the Tektronix Model 571 Curve Tracer to generate the forward I-V characteristic
curve for the Base-Collector Junction of the 2N3904 transistor.
i. Determine the limits for the B-C junction using the manufacturer specifications
sheet.
ii. Save a picture of the resulting curve, being sure to note the voltage and current
limits selected.
Copyright © 2015 GWU SEAS ECE Department
ECE 2115: Engineering Electronics
4
SEAS
Experiment #5: Characterization of an NPN Bipolar Junction Transistor (BJT)
Part II – Transistor Characterization Using a Test Circuit
In this part of the lab, you will generate only three I-V curves (IC vs. VCE) as you did in the prelab. IB will
be the parameter whose value will step from 10µA to 50µA in 20µA steps.
In the prelab, you generated an I-V curve for the 2N3904 transistor using the schematic in Figure P.1.
You were able to generate base current IB in the range of 0µA to 50µA. In the lab, the power supply can
behave as a current source, but it cannot produce a current as small as 50µA. To create the same family
of I-V curves in the lab, we must use the circuit in Figure 2.1. The voltage source combined with the
100kΩ resistor at the base will behave as the 0µA to 50µA current source from Figure P.1.
The data collected during this part of lab is to be recorded under the Measured column of Table P.1.
IC - Collector Current
RC
1kΩ
IB - Base Current
RB
VC
Q1
2N3904
VB
100kΩ
VCC
VBB
Figure 2.1 – BJT Test Circuit to Generate Family of I-V Curves
1. Measure the IB = 10µA curve.
a. Build the circuit depicted in Figure 2.1 using the 2N3904 BJT.
b. Measure the exact resistances of RB and RC using the DMM and record these values.
c. Use a DMM to measure the voltage at node VB in the circuit. This is VBE.
d. Use a DMM to measure the voltage at node VC in the circuit. This is VCE.
e. Adjust VCC until VCE equals 2V.
f. Adjust VBB until VBE equals the value found in the prelab when IB = 10µA and VCE = 2V.
g. Readjust VCC until VCE equals 0V.
h. Record VCC, VCE, VBB, and VBE in Table P.1.
i. Calculate the voltage across RB to calculate and record the current IB in Table P.1.
j. Calculate the voltage across RC to calculate and record the current IC in Table P.1.
k. Adjust VCE from 0V to 2V in 0.2V increments, repeating steps h-j at each step.
l. Adjust VCE from 2V to 10V in 1V increments, repeating steps h-j at each step.
m. Calculate β for each recorded value of IC and IB.
2. Measure the IB = 30µA curve.
a. Repeat steps a-m above, but in step f, adjust VBB until IB = 30µA. You will need to
calculate the current IB from the voltage across RB.
3. Measure the IB = 50µA curve.
a. Repeat steps a-m above, but in step f, adjust VBB until IB = 50µA. You will need to
calculate the current IB from the voltage across RB.
Copyright © 2015 GWU SEAS ECE Department
ECE 2115: Engineering Electronics
5
SEAS
Experiment #5: Characterization of an NPN Bipolar Junction Transistor (BJT)
POST-LAB ANALYSIS
1. Plot a family of I-V curves for the calculated and measured data collected in Table P.1.
2. Extract a few values for IB, VCE, IC, and VBE from the curve tracer plots. Place these in another
set of columns in Table P.1.
3. Compare the Calculated, Simulated, Measured (DMM and curve tracer measured values) via
graphs (overlaying them where possible) and percentage error in all cases.
Copyright © 2015 GWU SEAS ECE Department
ECE 2115: Engineering Electronics
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