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2 Laboratory Manual for Linear Electronics Laboratory Manual for Linear Electronics by James M. Fiore Version 1.1.4, 04 May 2015 Laboratory Manual for Linear Electronics 3 This Laboratory Manual for Linear Electronics, by James M. Fiore is copyrighted under the terms of a Creative Commons license: This work is freely redistributable for non-commercial use, share-alike with attribution Published by James M. Fiore via dissidents For more information or feedback, contact: James Fiore, Professor STEM Center Mohawk Valley Community College 1101 Sherman Drive Utica, NY 13501 jfioremvcc.edu or via www.dissidents.com Cover art by the author 4 Laboratory Manual for Linear Electronics Introduction This manual is intended for use in a linear semiconductor devices course and is appropriate for two and four year electrical engineering technology curriculums. The manual contains sufficient exercises for a typical 15 week course using a two to three hour practicum period. The topics cover basic diodes through DC biasing and AC analysis of small signal bipolar and FET amplifiers along with class A and B large signal analysis. For equipment, each lab station should include a dual adjustable DC power supply, a dual trace oscilloscope, a function generator and a quality DMM. Some exercises also make use of a distortion analyzer and a low distortion generator (generally, THD below 0.01%), although these portions may be bypassed. For components, a selection of standard value ¼ watt carbon film resistors ranging from a few ohms to a few megohms is required along with an array of typical capacitor values (film types recommended below 1 µF and aluminum electrolytics above). A decade resistance box and a 10 kΩ potentiometer may also be useful. Active devices include small signal diodes such as the 1N914 or 1N4148, the NZX5V1B or 1N751 zener, standard single LEDs, 2N3904 or 2N2222 NPN transistor, 2N3906 PNP transistor, and MPF102 N channel JFET. Each exercise begins with an Objective and a Theory Overview. The Equipment List follows with space provided for serial numbers and measured values of components. Schematics are presented next along with the step-by-step procedure. Many exercises include sections on troubleshooting and design. Simulations with Multisim are often presented as well, although any quality simulation package such as PSpice can be used instead. All data tables are grouped together, typically with columns for the theoretical and experimental results, along with a column for the percent deviations between them. Finally, a group of appropriate questions are presented. Other manuals in this series include DC and AC Electrical Circuits, Computer Programming with Python, and Embedded Controllers Using C and Arduino. A Note from the Author This manual is used at Mohawk Valley Community College in Utica, NY, for our ABET accredited AAS program in Electrical Engineering Technology. It was created out of a desire to offer an affordable lab manual for our students which covered the requisite material and made optimal use of our laboratory facilities. I am indebted to my students, co-workers and the MVCC family for their support and encouragement of this project. While it would have been possible to seek a traditional publisher for this work, as a long-time supporter and contributor to freeware and shareware computer software, I have decided instead to release this using a Creative Commons non-commercial, share-alike license. I encourage others to make use of this manual for their own work and to build upon it. If you do add to this effort, I would appreciate a notification. “It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are. If it doesn’t agree with experiment, it’s wrong.” - Richard Feynman Laboratory Manual for Linear Electronics 5 6 Laboratory Manual for Linear Electronics Table of Contents 1. Diode Curves . . . . . 8 2. The Zener Diode . . . . . 14 3. Base Bias . . . . . . 20 4. LED Driver Circuits . . . . . 26 5. Voltage Divider Bias . . . . . 32 6. Emitter Bias . . . . . . 38 7. Feedback Biasing . . . . . 44 8. PNP Transistors . . . . . 50 9. Common Emitter Amplifier . . . . 56 10. Swamped CE Amplifier . . . . 62 11. Voltage Follower . . . . . 68 12. Class A Power Analysis . . . . 74 13. Class B Power Analysis . . . . 80 14. Power Amp with Driver . . . . 86 15. JFET Bias . . . . . . 92 16. JFET Amplifiers . . . . . 98 Laboratory Manual for Linear Electronics 7 1 Diode Curves Objective The objective of this exercise is to examine the operation of the basic switching diode and to plot its characteristic curve. Theory Overview The basic diode is an asymmetric non-linear device. That is, its current-voltage characteristic is not a straight line and it is sensitive to the polarity of an applied voltage or current. When placed in forward bias (i.e. positive polarity from anode to cathode), the diode will behave much like a shorted switch and allow current flow. When reversed biased the diode will behave much like an open switch, allowing little current flow. Unlike switch, a silicon diode will exhibit an approximate .7 volt drop when forward biased. The precise voltage value will depend on the semiconductor material used. This volt drop is sometimes referred to as the knee voltage as the resulting I-V curve looks something like a bent knee. The effective instantaneous resistance of the diode above the turn-on threshold is very small, perhaps a few ohms or less, and is often ignored. Analysis of diode circuits typically proceeds by determining if the diode is forward or reversed biased, substituting the appropriate approximation for the device, and then solving for desired circuit parameters using typical analysis techniques. For example, when forward biased, a silicon diode can be thought of as a fixed .7 volt drop, and then KVL and KCL can be applied as needed. Equipment (1) Adjustable DC Power Supply model:________________ srn:__________________ (1) Digital Multimeter model:________________ srn:__________________ (2) Signal diodes (1N4148, 1N914) (1) 1 k Ω resistor ¼ watt actual: ________________________ (1) 10 k Ω resistor ¼ watt actual: ________________________ (1) 4.7 k Ω resistor ¼ watt actual: ________________________ 1N4148 Datasheet: http://www.fairchildsemi.com/ds/1N/1N4148.pdf 1N914 Datasheet: http://www.fairchildsemi.com/ds/1N/1N914.pdf 8 Laboratory Manual for Linear Electronics Schematics Figure 1.1 Figure 1.2 Figure 1.3 Procedure Forward Curve 1. Consider the circuit of Figure 1.1 using R = 1 kΩ. For any positive value of E, the diode should be forward biased. Once E exceeds the knee voltage, all of E (minus approximately .7 volts) drops across R. Thus, as E increases, so does the diode current. 2. Build the circuit of Figure 1.1 using R = 1 kΩ. Set E to 0 volts and measure both the diode's voltage and current and record the results in Table 1.1. Repeat this process for the remaining source voltages listed. 3. From the data collected in Table 1.1, plot the current versus voltage characteristic of the forward biased diode. Make sure V is the horizontal axis with I on the vertical. D D Reverse Curve 4. Consider the circuit of Figure 1.2 using R = 1 kΩ. For any positive value of E, the diode should be reversed biased. In this case, the diode should always behave like an open switch and thus no current should flow. If no current flows, the voltage across R should be zero, and thus the diode voltage should be equal to the applied source voltage. Note that the diode's voltage polarity is negative with respect to that of Figure 1.1. Laboratory Manual for Linear Electronics 9 5. Build the circuit of Figure 1.2 using R = 1 kΩ. Set E to 0 volts and measure both the diode's voltage and current and record the results in Table 1.2. Repeat this process for the remaining source voltages listed. 6. From the data collected in Table 1.2, plot the current versus voltage characteristic of the reverse biased diode. Make sure V is the horizontal axis with I on the vertical. D D Practical Analysis 7. Consider the circuit of Figure 1.3 using E = 12 volts, R1 = 10 kΩ and R2 = 4.7 kΩ. Analyze the circuit using the ideal .7 volt forward drop approximation and determine the voltages across the two resistors. Record the results in the first two columns of the first row (Variation 1) of Table 1.3. 8. Build the circuit of Figure 1.3 using E = 12 volts, R1 = 10 kΩ and R2 = 4.7 kΩ. Measure the voltages across the two resistors. Record the results in columns three and four of the first row (Variation 1) of Table 1.3. Also compute and record the percent deviations in columns four and five. 9. Reverse the direction of D1 and repeat steps 7 and 8 as Variation 2 in Table 1.3. 10. Return D1 to the original orientation and reverse the direction of D2. Repeat steps 7 and 8 as Variation 3 in Table 1.3. 11. Reverse the direction of both D1 and D2, and repeat steps 7 and 8 as Variation 4 in Table 1.3. Multisim 12. Repeat steps 7 through 11 using Multisim, recording the results in Table 1.4. 10 Laboratory Manual for Linear Electronics Data Tables E (volts) VD ID 0 .5 1 2 4 6 8 10 Table 1.1 E (volts) VD ID 0 1 2 5 10 15 Table 1.2 Variation V VR2 Theory VR1 Exp VR2 Exp % Dev VR1 % Dev V R1 Theory R2 1 2 3 4 Table 1.3 Laboratory Manual for Linear Electronics 11 V Variation VR1 Multisim R2 Multisim 1 2 3 4 Table 1.4 Questions 1. Is .7 volts a reasonable approximation for a forward bias potential? Is an open circuit a reasonable approximation for a reverse biased diode? Support your arguments with experimental data. 2. The "average" resistance of a forward biased diode can be computed by simply dividing the diode's voltage by its current. Using Table 1.1, determine the smallest average diode resistance (show work). 3. The instantaneous resistance (also known as AC resistance) of a diode may be approximated by taking the differences between adjacent current-voltage readings. That is, r = ΔV /ΔI . What diode diode diode are the smallest and largest resistances using Table 1.1 (show work)? Based on this, what would a plot of instantaneous diode resistance versus diode current look like? 4. If the circuit of Figure 1.3 had been constructed with LEDs in place of switching diodes, would there be any changes to the values measured in Table 1.3? Why/why not? 12 Laboratory Manual for Linear Electronics Laboratory Manual for Linear Electronics 13 2 The Zener Diode Objective The objective of this exercise is to examine the operation of the zener diode and to plot its characteristic curve. Theory Overview When forward biased, the zener diode behaves similarly to an ordinary switching diode, that is, it incurs a .7 volt drop for silicon devices. Unlike a switching diode, the zener is normally placed in reverse bias. If the circuit potential is high enough, the zener will exhibit a fixed voltage drop. This is called the zener potential or V . Manufacturer’s specify this voltage with respect to the zener test current, or I a point Z ZT; past the knee of the voltage-current curve. That is, if the zener’s current is at least equal to I , then its ZT voltage is approximately equal to the rated V . Above this current, even very large increases in current Z will produce only very modest changes in voltage. Therefore, for basic circuit analysis, the zener can be replaced mathematically by a fixed voltage source equal to V . Z Equipment (1) Adjustable DC Power Supply model:________________ srn:__________________ (1) Digital Multimeter model:________________ srn:__________________ (1) Zener diode around 5.1 volts (NZX5V1B, 1N751) (1) 2.2 k Ω resistor ¼ watt actual: ________________________ (1) 4.7 k Ω resistor ¼ watt actual: ________________________ NZX5V1B Datasheet: http://www.nxp.com/documents/data_sheet/NZX_SER.pdf 1N751 Datasheet: http://www.fairchildsemi.com/ds/1N/1N751A.pdf 14 Laboratory Manual for Linear Electronics Schematics Figure 2.1 Figure 2.2 Procedure Forward Curve 1. Consider the circuit of Figure 2.1 using R = 2.2 kΩ. For any positive value of E the zener is reverse biased. Until the zener potential is reached, the diode resistance is effectively infinite and thus no current flows. In this case the voltage across R is zero due to Ohm’s Law. Consequently, all of E should appear across the zener. Once the source exceeds the zener voltage, the remainder of E (i.e. E minus the zener potential) drops across R. Thus, as E increases, the circulating current increases but the voltage across the zener remains steady. 2. Build the circuit of Figure 2.1 using R = 2.2 kΩ. Set E to 0 volts and measure both the diode's voltage and current and record the results in Table 2.1. Repeat this process for the remaining source voltages listed. 3. From the data collected in Table 2.1, plot the current versus voltage characteristic of the forward biased diode. Make sure V is the horizontal axis with I on the vertical. D D Practical Analysis 4. Consider the circuit of Figure 2.2 using R1 = 2.2 kΩ and R2 = 4.7 kΩ. In general, to analyze circuits like this, first assume that the zener is out of the circuit and then compute the voltage across R2 using the voltage divider rule. If the resulting voltage is less than the zener potential then the zener is Laboratory Manual for Linear Electronics 15 inactive (high resistance) and does not affect the circuit. If, on the other hand, the resulting voltage is greater than the zener potential then the zener is active and will limit the voltage across R2 to V . Via Z KVL, the remainder of the voltage drops across R1 and from this the supply current may be determined. This current will then split between R2 and the zener. The R2 current is found using Ohm’s Law. The zener current is then found via KCL. Note that for higher and higher values of E, the voltage across (and therefore the current through) R2 does not change. Instead, all of the “excess” current from the source passes through the zener. 5. Build the circuit of Figure 2.2 using R1 = 2.2 kΩ and R2 = 4.7 kΩ. Set E to 2 volts. Compute the theoretical diode voltage and current, and record them in the first row of Table 2.2. Then measure the diode current and voltage and record in Table 2.2. Finally, compute and record the deviations. 6. Repeat step 5 for the remaining source voltages in Table 2.2. Multisim 7. Repeat steps 5 and 6 using Multisim, recording the results in Table 2.3. 16 Laboratory Manual for Linear Electronics Data Tables E (volts) VD ID 0 1 2 5 10 15 20 Table 2.1 E (volts) V I V I % Dev V % Dev I D Theory D Theory D Exp D Exp D D 2 5 10 15 20 Table 2.2 E (volts) V I D Multsim D Multisim 2 5 10 15 20 Table 2.3 Laboratory Manual for Linear Electronics 17 Questions 1. Is it safe to assume that the voltage across a zener is always equal to the rated V ? Why/why not? Z 2. The instantaneous resistance (also known as AC resistance) of a diode may be approximated by taking the differences between adjacent current-voltage readings. That is, r = ΔV /ΔI . What diode diode diode is the smallest effective resistance of the zener using Table 2.1 (show work)? 3. If the circuit of Figure 2.1 had been constructed with the zener reversed, how would this effect the results recorded in Table 2.1? 4. Assume that a diode with a much higher I rating (say, 100 mA) was used in this exercise. In ZT general, what would the likely outcome be for the circuit of Figure 2.2? 18 Laboratory Manual for Linear Electronics Laboratory Manual for Linear Electronics 19 3 Base Bias: CE Configuration Objective The objective of this exercise is to explore the operation of a basic common emitter biasing configuration for bipolar junction transistors, namely fixed base bias. Along with the general operation of the transistor and the circuit itself, circuit stability with changes in beta is also examined. Theory Overview For a bipolar junction transistor to operate properly, the base-emitter junction must be forward biased while the collector-base junction must be reverse biased. This will place V at approximately .7 volts and BE the collector current I will be equal to the base current I times the current gain β. For small signal C B devices, the current gain is greater than 100 typically. Thus, I I and I I . C B C≈ E The common emitter configuration places the emitter terminal at ground. The base terminal is seen as the input and the collector as the output. Using a fixed base supply, the base current is dependent on the value of the base resistor via Ohm’s law. Consequently, any variation in current gain across a batch of transistors will show up as an equivalent variation in collector current, and by extension, a variation in collector-emitter voltage V . CE Equipment (1) Dual Adjustable DC Power Supply model:________________ srn:__________________ (1) Digital Multimeter model:________________ srn:__________________ (3) Small signal NPN transistors (2N3904) (1) 1.2 k Ω resistor ¼ watt actual: ________________________ (1) 330 k Ω resistor ¼ watt actual: ________________________ 2N3904 Datasheet: http://www.fairchildsemi.com/ds/2N/2N3904.pdf 20 Laboratory Manual for Linear Electronics

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