Lab 3

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University of Michigan, Dearborn *

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ECE 311

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Electrical Engineering

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Feb 20, 2024

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ECE 311: Electronic Circuits 1 (Fall 2017) Lab 3 : BJTs Part I By Kayleigh James (UMID: 81519321) November 4th, 2017 Fall 2017 Honor Code: I have neither given nor received unauthorized assistance on this graded report. X_____________________________________________________________________
Abstract The purpose of this lab is to investigate the bip junction transistor characteristic in DC. The input and output characteristic of an NPN transistor (2N2222) will also be examined in this laboratory experiment. These goals will be accomplished by completing both a software simulation and a hardware experiment. We will use both of these methods in order to explore the output characteristics of these BJTs. Introduction and Background The purpose of this experiment is to confirm the output and input characteristics of BJTs that we have seen in lecture examples and the homework. By performing both the software and hardware portions of this labs, we will develope a better understanding of BJTs through taking measurements and constructing graphs. In order to complete this lab, background knowledge of BJT operation regions (cutoff, active, and saturation) is necessary. Also, to create the graphs we must have basic knowledge of circuit analysis and Ohm’s Law. Pre-Lab Questions and Answers 1. Circuit symbols for NPN and PNP transistors: 2. Cutoff Region: The transistor acts like a wire (short circuit). There is no impedance between the emitter and collector.
Active Region: The transistor acts proportional to the current flowing into the base. Saturation Region: The transistor behaves as an open circuit. There is infinite impedance between the emitter and collector. Mode CBJ EBJ Active Mode Reverse Forward Cutoff Mode Reverse Reverse Saturation Mode Forward Forward 3. 2N2222 Pin Out from datasheet: 4. Input and Output Characteristics of a Transistor: Input Characteristics: We can observe the input characteristic of a transistor by measuring Ic and Vce. Vce can be readily measured, but in order to measure Ic we must perform some calculations. To determine the value of Ic, we must find out Vc first, we then say that Ic = (Vc- Vce)/R3. If we analyze the graph of the input characteristic for the transistor, we can see the saturation, active, and cutoff regions. The transistor is in saturation mode when Vce is low resulting in CBJ being in forward bias. If the CBJ becomes reverse biased, the curve will display the active region of the transistor. Finally, if Ic is low, we can see that the curve shows the cutoff region of the transistor. Output Characteristics: In order to observe the transistor’s output characteristic we must measure Vbe and Ib. Once again, Vbe is easily measured but in order to find the value of Ib we must perform some calculations. Here, we say that Ib = (Vbb-Vbe)/R2. In our software
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simulation, Vbb will be fixed and Vbe will be set to a constant 0.7V since it will be operating in the active region. The output characteristic will be similar to the output characteristic of a diode (the slope will be near 0 that rapidly increases to a slope approaching infinity). Simulation Part 1: Transistor Output Characteristic Image 1: The schematic for the circuit using a 330kΩ resistor. Image 2: Transistor Measurement table using a 330kΩ resistor.
Image 3: Graph using Image 2 data for the 330kΩ resistor. Image 4: The schematic for the circuit using a 147kΩ resistor.
Image 5: Transistor Measurement table using a 147kΩ resistor. Image 6: Graph using Image 5 data for the 147kΩ resistor. Part 2: Transistor Input Characteristic
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Image 7: Circuit Schematic using a 330kΩ resistor. Image 8: Output Waveform for the Transistor Input Characteristic Now calculate the input impedance by evaluating the slope around Vbe = 0.7V; Rin = Rbe = ΔVbe/ΔIb. Rin = 29.39/17.35 = 1.694 kΩ Hardware Part 1: Transistor Output Characteristic
Image 9: Measurements using a 330kΩ Resistor (Actual value was around 326kΩ) Image 10: Graph of transistor output using data from Image 9
Image 11: Measurements using a 147kΩ Resistor (Actual value was around 145kΩ) Image 12: Graph of transistor output using data from Image 11
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Discussion of Results 1. How to find out a minimum value of input voltage source Vbb that makes the transistor enter the linear region. The transistor will enter the linear region if it is operating in active mode. If we want the transistor to operate in active mode, then the CBJ must be reverse biased and the EBJ must be forward biased. This situation will occur if we set Vbe to be greater than or equal to 0.7V. In this circuit design, Ve is 0V so Vbb must be 0.7V or greater. 2. Provide a quantitative analysis on the results/curves from the experiment. In the simulation portion of this lab, we generated the output characteristic of a transistor that utilized a 330kΩ resistor. From the graph (image 3) we can see that this transistor was operating in the saturation region when Vce was between 0 and 0.5V. Once Vce exceeded 0.5V, the transistor was then operating in active mode. In this region, Ic was between about 4.6 to 5.1 mA. When we changed from a 330kΩ resistor to a 147kΩ resistor, the transistor then operated in saturation mode whenever Vce was between about 0 and 0.2V. Once exceeding 0.2V, the transistor was then operating in active mode. Once in active mode, Ic was between about 11 and 12mA. For the hardware portion of the lab, we generated a output characteristic curve for a 330kΩ resistor which can been seen in image 10. From the graph we can tell that the transistor was operating in saturation mode when Vce was between about 0 and 0.4V. Once exceeding this 0.4V value, it then began to operate in active mode. Once in the active region, Ic was between about 4.9 and 5.3mA. Once we changed the 330kΩ resistor to a 147kΩ resistor, the curve changed and can be seen in image 12. In this case, the transistor was operating in saturation mode when Vce was between roughly 0 and 0.3V. Once exceeding 0.3V, the transistor then was in the active region. Once in this active region, the Ic went from about 10 to 12mA. 3. Quantitatively compare the results/curves from the experiment and PSpice simulation.
The curves were very similar between the hardware and software portions of this lab. The slight differences between the curves can be attributed to the actual resistors used in the hardware portion having slightly different resistances than labeled. With the 330kΩ resistor in hardware and software, it was operating in the saturation region between about 0 and 0.4V. Once it switched to active mode, Ic was around 5mA for both hardware and software. For the 147kΩ resistor, both situations show the transistor operating in the saturation region between about 0 and 0.2V. After exceeding this value, the transistor operates in the active region where Ic is around 11.5mA for both hardware and software. Conclusion In this lab, we experienced how the changing the resistor used in a transistor can affect the input and output characteristics of a transistor. We also learned how we can calculate input resistance by utilizing the input characteristic curve. Any discrepancies between the hardware and software curves can be attributed to the actual resistors used in the hardware portion of the lab having different resistances than the ideal resistors used in the PSpice simulation. References 1. https://www.onsemi.com/pub_link/Collateral/P2N2222A-D.PDF 2. http://macao.communications.museum/eng/exhibition/secondfloor/MoreInfo/ 2_10_3_HowTransistorWorks.html 3. http://www.electronics-tutorials.ws/transistor/tran_1.html