# lab6 - University of California San Diego Department of...

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University of California, San Diego Department of Electrical and Computer Engineering ECE65, Fall 2009 Lab 6, BJT Amplifiers Note: All transistor experiments in this Lab are done with 2N3904 NPN transistor. For your analytical analysis use the following values: β = 200, r π = h ie = 3 kΩ, β = h fe = 200, and h oe = 10 μ S. Use formulas for transistor amplifiers in the lecture notes and see problems in “transisors part 2” lecture notes.. R C V CC R B Experiment 1: Poor biasing Set up the circuit with R B = 1 . 5 MΩ, R C = 5 kΩ, and V CC = 15 V. Circuit Analysis: Compute I C , I B , and V CE . PSpice Simulation: a) Simulate the circuit with PSpice (bias point details only) and compare values of I C , I B , V CE , and V BE from PSpice simulations with your analytical calculations. b) Rerun your PSpice simulations for temperatures of 0 and 60 C. Make a table of I C , I B , V CE , and V BE for the above temperatures and that of part a (which is for default temperature). Explain your observations. Lab Exercise: a) Set up the circuit and measure I C , I B , I E , V CE , and V BE . Note that these measurements are not straightforward. You have to consider the sensitivity of your meter as well as its internal resistance. In some cases, you have to measure the quantities “indirectly.” Check if the transistor obeys KVL and KCL. b) Compare your measurements of I C , I B , V CE , and V BE with your PSpice simulations. Explain why they are different. c) Set the voltmeter to measure V CE . Hold the transistor between two fingers without touching the rest of the circuit. Transistor will warm up slightly by your body temperature. What happens to V CE as transistor warms up? Explain your observations.

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ECE65, Lab 7 Exercises Page 2 Experiment 2: Good biasing R C R 1 V CC R 2 R E - Set up the circuit with R 2 = 12 kΩ, R 1 = 39 kΩ, R C = 2 kΩ, R E = 1 kΩ, and V CC = 15 V.
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