Semiconductors - Circuits and Electronics for Mechanical Engineers | ECEN 3010, Lab Reports of Electrical and Electronics Engineering

Download Semiconductors - Circuits and Electronics for Mechanical Engineers | ECEN 3010 and more Lab Reports Electrical and Electronics Engineering in PDF only on Docsity! ECEN 3010 Lab Circuits and Electronics University of Colorado at Boulder Lab #4 Semiconductors Names of All Participating Lab Partners: Lab Section (Circle One): M T W Th F Learning Objectives This lab will introduce you to basic semiconductor components (diodes and transistors) and will demonstrate how these components are used to create common circuits. Minimum Parts Required One 2N3904 transistor, four 1N4148 diodes, an LED, and various resistors and capacitors. Part 1 – Diodes Use the function generator to produce a 120 Hz, 5-volt amplitude sinusoidal voltage waveform. Set the DC offset to zero. 1.1) Construct the circuit in Figure 1 using a 1N4148 diode. The 1N4148 diodes are small, translucent, rust-colored cylinders. The stripe on the diode package indicates the cathode lead of the diode. Use a 22 Kohm resistor for R1. ECEN 3010 Lab 4 Page 1 of 7 Rev. 2008-08-24 This material is subject to copyright notice on last page. Output 1N4148 R1 Input Figure 1. Diode circuit. 1.2) Use the oscilloscope to observe the output. Draw the output waveform and label the voltage/div and the time/div axes. 1.3) What is the name of this circuit (it was discussed in lecture and in the textbook)? What is its use? 1.4) How would the output be different if you used an ideal diode rather than an actual diode? Use the specifications of the 1N4148 to support your answer (from www.fairchildsemi.com). ECEN 3010 Lab 4 Page 2 of 7 Rev. 2008-08-24 This material is subject to copyright notice on last page. Part 2 – Transistor as a Switch (Saturation) You will use a 20 Hz signal from the function generator to cause an LED to flash. You will use a transistor to as the LED current driver. 20 Hz Square wave from Function Generator R1 Vcc = 5 V LED R2 Q1 Figure 4. Transistor circuit. The output current capability of the function generator is low, so you will use R1 to limit the current into the base of the transistor. You will limit the current to 2 mA. The maximum voltage across R1 will be 5 volts from the function generator minus the base- emitter voltage (VBE) of the transistor. The node voltage of the base of the transistor will be VBE since the emitter is connected to ground. 2.1) Assume that VBE= 0.6V. Calculate the ideal resistance value of R1 to limit the base current to 2 mA. What resistor from your kit will you use? 2.2) Use a red LED from your kit. The allowable current through the LED is 25 mA. The forward voltage across the LED is specified to be 1.8 V. Assume that VCE = 0.2V when the transistor is in saturation. What voltage is needed across resistor R2? Calculate the ideal resistance value needed for R2. What resistor from your kit will you use? 2.3) Build the circuit on your breadboard. The input to the base resistor should be a 0- to-5 V, 20 Hz square wave (5Vpp, 2.5V DC offset). The anode (positive) lead of the LED is slightly longer than the cathode (negative) lead. With the circuit ECEN 3010 Lab 4 Page 5 of 7 Rev. 2008-08-24 This material is subject to copyright notice on last page. powered with the power supply and the function generator on, can you see the LED flash? 2.4) Change the duty cycle on the function generator to 20%. Place an oscilloscope probe in the circuit to measure the node voltage at the base of the transistor; place a second oscilloscope probe in the circuit to measure the node voltage at the collector of the transistor. Compare the waveform at the base to the waveform at the collector. Are they different? If so, why are they different? 2.5) What is the measured VCE in this circuit when the transistor is in saturation (with the base current at 2 mA in this circuit)? (Measure the lower portion of the square wave at the collector. It will be near, but not at, ground.) 2.6) Change R1 to 220 KOhm while using the same R2. Measure the voltages at the base and the collector of the transistor. What is VCE in this circuit? Calculate β for the transistor with the new R1. Is it operating in the linear or saturated region? Part 3 – Transistor Amplifier (Optional. Up to 10% Extra Credit) 3.1) Assemble the circuit shown in Figure 5. The power supply and function generator should be turned off during assembly. Observe the polarity of the capacitors. Combine the 2.2µF and 4.7µF capacitors to make the 6.9µF capacitor. 3.2) If you have a wire connected from the signal generator to your breadboard for a previous circuit, disconnect it for now. Turn on the function generator and set it to produce a 1 KHz, 1Vpp sine wave with zero offset. 3.3) Turn on the power supply and apply power to your circuit. Using the multimeter or an oscilloscope probe, measure the voltages at the three transistor terminals. These voltages should be approximately 9 V (collector), 3.4 V (base), and 2.8 V (emitter). If your measured voltages are off by a few tenths of a volt, this is not a concern, but it is important that the voltage at the collector be several volts above the base voltage, and the base voltage should be higher than the emitter voltage by approximately 0.6 V to 0.7 V. Measure Vce. Is the transistor operating in the active (linear) or saturated region? 3.4) Connect the function generator to the circuit and use two oscilloscope probes to measure the input and output node voltages. Use the voltage measurement functions to measure the peak-to-peak voltages at the input and output terminals. Adjust the function generator to so you can measure four Vin, Vout pairs: set the Vin (peak-to-peak) to 1.0 V, 1.5 V, 2.0 V, and 2.5 V. Measure Vin and Vout for each case. Determine the gain, Vout/Vin, over the range of values. 3.5) Increase the function generator output amplitude so that you can observe distortion in the output waveform. At first the sinusoid should appear lopsided, ECEN 3010 Lab 4 Page 6 of 7 Rev. 2008-08-24 This material is subject to copyright notice on last page. and then you should see distinct clipping of the waveform peaks. At what voltage values does the clipping occur (top and bottom of the output waveform)? 3.7) Return the function generator output to a level that does not cause distortion. Increase the frequency of the input sinusoid. How is the output affected? 100k 51k 4.7k 2.2k 15k 6.9uF 100uF Function Generator Vcc = 15 V Output 2N3904 Input Figure 5. Transistor amplifier circuit. Copyright Notice: Original documents and labs created in 2005 by Derek Reamon. Subsequent modifications and additions authored by William Newhall and James Avery. No part of this document may be distributed in any form without the written consent of the copyright holders. ECEN 3010 Lab 4 Page 7 of 7 Rev. 2008-08-24 This material is subject to copyright notice on last page.