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Department of Electrical Engineering
Faculty Member: ______Saqib Nazir____ Dated: 20-10-19
Semester:___3rd__________ Section: _____B________
EE215: ELECTRONIC DEVICES AND CIRCUITS
Lab 8: BJT
I-V characteristics and Type Identification
PLO4 PLO5 PLO8 PLO
Name Reg. No Viva / Quiz / Lab Performan ce
Analysis of data in Lab Report
Modern Tool Usage
Ethics and Safety
Individual and Team Work
5 Marks 5 Marks 5 Marks 5 Marks 5 Marks Maryam Mahmood 257913
Iram Fatima Aulakh 249796
Sahar Zahid 257831
LABORATORY EXERCISE-
BJT I-V Characteristics and type identification
Objective: To study current-voltage characteristics of BJTs
- The primary purpose of this lab is to develop a working knowledge of Bipolar Junction Transistor (BJT). Transistors are current controlled devices which find applications in a vast array of circuits including but not limited to amplifiers, electronic switches, multipliers etc.
- First, the students will learn the method that is used to determine the type of the transistor and find out and label various terminals of the BJT.
- Second parts deals with the study the I-V characteristics of the BJT, and see how varying the parameters of the BJT affect them. For our implementation and simulation phase the 2N2222A transistor will be used which is one of the popular type of BJT around.
Required Resources
The following components, test equipment and software would be required.
- 2N2222A Transistor
- DMM
- Oscilloscope
- Resistors
- Capacitors
- Power Supply
- PSpice Simulation Software.
The Experiment
The experiment is broken down in two exercises; one of the experiment is divided into two parts namely:simulation and implementation. You are required to observe and record the simulation/ implementation results and answer the given questions. Include your answers in your lab reports.
Exercise 1: BJT Type Identification (Implementation-I)
In this part of the experiment you will be given a sample transistor and using the procedure below you are required to determine whether the transistor is an NPN or PNP transistor. You are also required to identify the terminals of the transistor.
Procedure
- Set your digital multi-meter to diode check mode.
- Identify each of the terminals. •.1. Emitter •.2. Base •.3. (^) Collector
- Explain why the diode check reading for the collector base junction is lower than the emitter base junction?
The emitter-base PN junction has a slightly greater forward voltage drop than the collector- base PN junction, because of heavier doping of the emitter semiconductor layer
- How will you determine whether the transistor is NPN or PNP type?
As 2-3 and 2-1 are both positive voltages (from table), so we can say that 2 is base and it’s a p- type region. Hence our transistor is an NPN type transistor.
Exercise 2 Part A:
Common Emitter I-V Characteristics of the BJT (Simulation-I)
In this part the students will study the common emitter I-V characteristics of a BJT. In particular relationship between the collector current and the voltage that appears across the collector- emitter junction of the transistor will be observed. Further, the effect of various parameters like, saturation current, early voltage etc. on the transistor I-V characteristics will be studied.
Procedure:
- Using OrCad PSpice software, draw the circuit as shown in figure 2A.
- The test circuit in figure 2A is used to determine the dependence of the collector current on the base-emitter voltage as well as the voltage applied at the collector. The source VBB in figure 2A controls the amount of base-emitter voltage and the current that enters the base terminal and the source VCC controls the voltage that appears at the collector terminal.
- In the first simulation run, set the value of R 1 = 1Ω.
- Create an appropriate simulation profile and perform DC Sweep Analysis.
- In the Primary Sweep tab, specify the voltage source as VCC. Vary it from 0 to 30 V.
- Run the simulation and make use of axis variables and traces to get a graph between the collector current and. (Hint: The emitter is grounded so is effectively equal to VC).
- Use Axis Setting Option to get different views of the V-I curve. Select different settings and save the graphs that depict the BJT graphs which are easily readable.
R1 = 1 KΩ
- Now do a second simulation run using R 1 = 220Ω. Repeat steps (4) to (8)
R1 = 220 Ω
V BB i B
0.7 14.585 uA
0.6 5.228 uA
0.5 1.2714 uA
0.4 258.35 nA
- Calculate the average value of β for each value of base current. Comment on and explain the trend that you observe.
IC (0.4 V) IC (0.5 V)
IC (0.6 V) IC (0.7 V)
V BB i B ic β
0.4 258.35 nA 27.2 uA 105.
0.5 1.2714 uA 172.238 uA 135.
0.6 5.228 uA 846.833 uA 162.
0.7 14.585 uA 2.616 mA 179.
- On the I (^) C versus VCE plot, identify each region of operation of the transistor.
Saturated region
Active regionCut-off region
- Why does the graph of the collector current have a considerable slope in the active region of the transistor? Explain.
Because of Early Effect, as VCE increases, i (^) c also increases. This is known as early effect which is responsible for the slope in the graph.
- Calculate the Early voltage of the transistor using the plot that you have obtained.
x 1 = 9.507 V x 2 = 14.335 V y 1 = 2.6004 mA y 2 = 2.7500 mA
m = =^ 0.
So; y = mx +c y = 0.031x + c c = 2.*
- For a fixed value of VBB, vary V (^) CC in steps of 1V and record the values of I (^) B, I (^) C and VCE. Take sufficient readings.
- Change the value of VBB in steps of 0.1V and for each valve of V (^) BB ,calculate and tabulate the values of β.
- Plot the collector current versus collector emitter voltage using your data points in MS Excel and include it in your report
Figure 2B – Circuit Diagram for Implementation-II
V (^) BB (V) VCC (V ) I (^) B (uA) I (^) C (uA) VCE (V) Beta 0.4 4 0.62 2.11 4.0190 3. 5 0.63 1.69 5.0655 2. 6 0.18 1.66 6.063 9. 7 0.12 1.15 7.020 9. 8 0.10 0.20 8.072 2 9 0.07 0.18 9.051 2. 0.5 4 0.01 0.16 3.969 16 5 0.03 0.17 4.905 5. 6 0.01 0.17 5.908 17 7 0.02 0.19 6.785 9. 8 0.07 0.15 7.990 2. 9 0.05 0.20 8.972 4 0.6 4 0.37 1.54 3.945 4. 5 0.38 1.51 4.988 3. 6 0.38 1.48 5.936 3. 7 0.37 1.45 6.963 3. 8 0.356 1.41 8.076 4. 9 0.372 1.43 8.945 3. 0.7 4 3.912 506 3.69 129. 5 3.962 542 4.86 136. 6 3.978 559 5.89 140. 7 3.995 565 6.933 141. 8 4.068 587 7.89 144. 9 4.099 609 8.86 148.
Observations/Measurements and Explanations
Answer the following questions:
- Compare the graphs that you have obtained from Simulation-I and Implementation-II. Are they similar? If not, explain the differences.
The graphs are not entirely similar as in implementation, we have only graphed the transistor in active mode while in simulation, we’ve graphed it in saturation mode too.
- Calculate the early voltage based on the I (^) C-V (^) CE graphs that you have obtained. Compare with the value that you have obtained from Simulation- I.
x 1 = 4.860 V x 2 = 7.89 V y 1 = 565 uA y 2 = 587 uA
m = =^ 7.
So; y = mx +c y = 7.26x + c c = 529*
For VA , putting y = 0;
0 = 7.26 VA + 529 VA =* = - 72.8 V
The values are approximately same.
- Try and change the values of the resistances and observe its effect on the IC -V (^) CE curve. What changes do you observe? Is there any change in the slope of the graph in the active region? Comment in each case.
