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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docx

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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
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.
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