# Lab 2 - Lab2Notes Prelab...

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Lab 2 Notes Prelab: Only Parts 1 and 3 will be graded. You are encouraged, but not required, to attempt all parts. Experiments: Only Parts 1 and 3 will be graded. However, you are required to attempt all parts. You may not leave lab early unless the TA signs off on all parts.

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© ECE 220 Lab 2 revised July 2008 by R. N. Strickland ECE 220 Lab 2 Circuit analysis using node voltage & mesh current methods Design of a voltage/current meter Building a transistor amplifier This lab is intended to reinforce the ckt analysis tools covered in the early part of Chapter 4 of the text. The design component requires you to build a simple current/voltage meter (Chapter 3). One of the lab experi- ments requires you to build a transistor amplifier circuit (mostly for the experience and fun). We introduce AC quantities, specifically root-mean-square (rms) voltage and current. The use of rms quantities in resis- tive AC ckts follows directly from DC ckts. For example, Ohm’s Law can be stated as: ckts) (AC R i v ckts) (DC iR v rms rms = = The digital multimeter (DMM) gives rms readings of current and voltage on the "AC" setting. The new lab skills introduced are: Measuring AC voltage and current using the DMM Measuring DC voltage using the oscilloscope Measuring peak-to-peak of AC voltage waveforms using the oscilloscope Operating the oscilloscope in dual trace mode The measurement techniques employed in Lab 1 will also be employed. Prelab (30 points) PRINT ALL PSPICE SCHEMATICS ( PSpice exercises are integrated throughout the Prelab.) 0 R4 LED 0 0 1.65V Is LED R5 R2 R3 R1 C A 2V 2V B Fig. 1 Node/Mesh example: Bridge ckt with a p of LEDs Each LED conducting in the forward direc- tion drops ~ 2V. air Part 1: Node/Mesh example (with LH3330 Light Emitting Diodes) The ckt in Fig. 1 has component values: I s = 20mA, R 1 = 240 , R 2 =150 , R 3 is to be found, R 4 =330 , and R 5 =110 . Each forward-biased LH3330 (or equivalent part no.) red LED can be modeled as an ideal voltage source of value 2V. (a) Use mesh and/or node analysis to find the value of R 3 that makes the LED’s equally bright (i.e. each LED passes the same amount of current). Show your work. 1
© ECE 220 Lab 2 revised July 2008 by R. N. Strickland (b) Using this value for R 3 , compute all the essential branch currents (including the two LED currents) and all the essential node voltages in the ckt . (c) Now set R 3 to zero ohms, and use NVA to find all node voltages and branch currents. (Different values to part (b), of course.) Show all work. (d) Draw and simulate the ckts from (b) and (c) in PSpice to verify your answers, using a 2V voltage source in place of each LED. (The LH3330 is not included in the PSpice libraries.) (e) For the ckt from part (b), find all node voltages and branch currents with the LEDs reversed. (Hint: The behavior of reversed diodes makes the calculations relatively simple to perform.) Check your answers on your PSpice schematic, this time using a D1N4002 diode component 1 (re- versed of course). There is no need to submit a schematic for this part.

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Lab 2 - Lab2Notes Prelab...

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