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# CALVIN ENGR 311 - BJTs Lab

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ENGR 311 Lab - October 24, 2002ENGR 311 Lab - October 24, 2002BJTs The objective of this lab is to investigate the characteristics and operation of the bipolar junction transistor(BJT). Determination of .Gathering data for the static characteristicsThe dc analysis of BJT circuit.The transistor which will be used in this lab is the 2N3904 (npn) transistor.Experiment1. Determine the approximate value of  for your transistor circuit below. You should note that data bookstypically give a wide range of beta for transistors. For example, the National Semiconductor data book lists for the 2N3904 as ranging from 60 to 360 with a typical value of 150 when IC = 10mA and VCE = 5v.Measure the actual values of the two resistors using the RLC bridge, and wire the circuit shown in Figure 1 (seethe transistor pinout below).Additionally, measure the actual value of a 1k resistor and place it in series with the 100k resistor. This willact as a "low" impedance shunt for measuring the base current of the transistor. The 100k resistor and the inputimpedance of the Kiethley DMM's are too similar and the DMM presents an alternate, and sometimes significantpath for current to flow.The first thing to determine if a transistor circuit is operating properly is to see if you have base control. Thiscan be accomplished by varying VBB, observing the variation in IB (the voltage drop across RB), and alsoobserving the variation in IC with IB (the voltage drop across RC).Set VBB such that IC does not exceed 10mA (the exact value is not important) and observe IB and IC. Calculate and compare your values with those from two more people in your class. Also compare with PSpice results andthe TestMate 175 Multimeter.2. Using the circuit shown below, set VBB such that IB = 20A. Set VCC = 0 initially, then increase VCC andobserve the behavior of IC vs. VCE for VCE = 0 - 10V. Be sure to verify that IB remains a constant throughout this procedure. With data try to construct a characteristiccurve if you can. ReportReport the measured values of .Graph IC vs. VCE if possible. Using your characteristic curves, estimate the Early voltage for your transistor if possible. Using the actual values for , VBE and the resistors, calculate the theoretical values of IC, IB and VCE (use alsoPSpice) and compare these to the measured

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