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Physics and Astronomy
PHYS 3050
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PHYS 3050 Lab Report VI The Transistor as a Switch Swapnil Agrawal 210049237 3rd December 2009 Swapnil Agrawal - 210049237 Table of Contents 1. INTRODCTION 2 1. Background 2 2. Aim 2 3. Apparatus 2 2. ANALYSIS, CALCULATIONS AND OBSERVATIONS 3 1. Rise and Fall Times 3 2. A NOT Gate 7 3. SOURCES OF ERROR 8 4. CONCLUSION 8 5. REFERENCES 8 1 Swapnil Agrawal - 210049237 INTRODUCTION 1. Background The transistor, like the diode, utilizes the property of the PN junction in a semiconductor. Unlike the diode, the transistor is a three-port device (with the three ports referred to as the Base (B), Collector (C), and Emitter (E). The collector and the emitter regions are similarly doped (either p-type or n-type) while the base is oppositely doped. Hence there are two types of transistors - so called NPN and PNP transistors. The main functions of transistors are as switches and amplifiers. A logic gate performs a logical operation on one or more logic inputs and produces a single logic output. The logic normally performed is Boolean logic and is most commonly found in digital circuits. Logic gates are primarily implemented electronically using diodes or transistors. 2. AIM The purpose of this lab is to understand the characteristics of a simple transistor when it is used as a switch and build a simple transistor logic gate. 3. APPARATUS a) Agilent 33120A function/Arbitrary Waveform Generator b) Agilent 3630A Triple Output DC Power Supply c) Tektronix TDS200 Digital Storage Oscilloscope (DSO) d) Breadboard, Resistors and 2N3904 (NPN) 2N3906 (PNP) Transistor. e) Red and Green LED. 2 Swapnil Agrawal - 210049237 ANALYSIS, CALCULATIONS AND OBSERVATIONS 6.1 Rise and Fall Times Because of the underlying physics of the PN junctions, the transistor cannot instantly turn off and on. The rise time of the output signal, t , is defned as the time it takes the r output to rise from 10% to 90% of its final "ON" value. Similarly, the fall timef t , is the time it takes to fall from 90% to 10%. There is also a storage time, ts, which is the time between when the input has gone to zero and when the output falls to 90% of it's ON value. This is illustrated in the figure below: Circuit Construction The circuit shown on the next page is constructed. All components are checked before they are used in the circuit. inis the square wave from the signal generator with V PP about 10 V and a frequency of 1 kHz. The bias voltage V obbabout +10 V is supplied by the +20 V output of the Power Supply. We used the 2N3904 NPN transistor. The following values of resistances were used: R B RC Low (R B1 355 Ω 977 Ω High (R B2 46.6 kΩ 977 Ω For the transistor used: Legs Voltage BE 0.68 V BC 0.64 V 3 Swapnil Agrawal - 210049237 Resistor Rise Time (t r Fall Time (tf) Delay Time (t s Vin 40 ns 40 ns N/A V R 16 ns 240 ns 25 ns out B1 V outRB2 800 ns 400 ns 100 n
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