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					                    LABORATORY EXERCISE #2 - DIODE PROPERTIES

Objective: to become familiar with the basic properties of junction diodes.

Components: 2 1N4002 diodes, 1 1N4742 Zener diode, resistors as follows: 1 200-, 1 510-,
and 2 1-k.

1. Diode Characteristics
   (A plot of diode current vs. diode voltage is called a diode characteristic.)
  a. Take one of your 1N4002 diodes into the electronics lab and put it on the curve tracer. Your
      TA will show you how to use the curve tracer.
  b. Very carefully draw what you see on the screen in your notebook.
  c. A diode and its circuit symbol are shown in Figure 2.1. Construct the circuit shown in Figure
      2.2, connecting +VS to one of the dc supplies in your dual power supply.
  d. Adjust VA to approximately 0.1 V; measure both VA and VB.
  e. Increase VS in steps of 0.1 from 0.1 to 1.0 V, then in steps of 1 V to 6 V, then in steps of 2 V
      to 12 V. Record the measured value of VA and VB for each step.
  f. Calculate the value of the diode current for each step.
  g. Plot the diode current vs. the diode voltage, VB, and compare the curve you saw on the curve
      tracer.
  h. Carefully label this diode number 1 and the other 1N4002 diode number 2.

2. Diode Parameters
  a. With the same circuit, Figure 2.1, adjust VS to +10 V.
  b. Measure VA and VB.
  c. Turn the power off.
  d. Remove the 1-k resistor, label this resistor 1.
  e. Replace it with the other 1-k resistor.
  f. Turn the power on and remeasure VA and VB.
  g. Repeat these measurements for diode number 2.
  h. For each of the four cases, calculate the current through the diode.
   i. Using the two measurements on the same diode, for each diode calculate nVT, IS, rd, and the
      current through the diode when the voltage is 0.7 V. (Hint: use equations 3.3, 3.4, and/or
      3.5 and 3.18 and/or 3.19 in the text.)
   j. Make a results table with columns for diode number, nVT, IS, rd, and I0.7V. Enter your
      results in the first two rows of this table.
  k. Collect results from other teams and add them to your results table. Identify each set of
      results with the names of the members of the team you got it from. If any values look
      unreasonable, check to see that they were calculated correctly.
  l. Find the average and standard deviation for each of the parameters in the results table.
3. Zener Diodes
  a. Go to a data book and look up your Zener diode, 1N4742. Record the nominal Zener
      voltage, the nominal current at that voltage, and the Zener resistance. If the data book gives
      minimum, maximum and typicals, record all three (or as many as there are) for each of the
      parameters. Write down the title, publisher, & date of the data book and the page number
      where you found the information. (If your TA doesn't explain how to read the data book,
      there is a section in the data book that does: read it.)
  b. Construct the circuit shown in Figure 2.3.
  c. Set VS to +20VDC and measure VA and VB. Calculate IZ.
EE 345                       LAB # 2 - DIODE PROPERTIES                             PAGE 1
 d. Reduce VS to +19VDC and repeat the measurements and calculation.
 e. Calculate the Zener resistance using rZ = VB/ IZ. Compare this result to the nominal
    value found in the data tables.
 f. Calculate the error in the output voltage due to the variation in the input voltage: Errout = 
    VB/VB, using the value of VB from part 3.c above.
 g. Calculate the error in the input voltage: Errin = VA/VA, using the value of VA from part 3.c
    above.
 h. Compare the disturbance in the output voltage to the disturbance in the input voltage (3.f and
    3.g above).

                 V                          VS                          VS
             + D-
                                                 VA                             VA
         +                -
                                    1 k                       200
         Diode band
                                                 VB                             VB
         +                -
                                   1N4002                     1N4742
             +        -
                 vz
       Figure 2.1. Diode and Figure 2.2. Circuit for      Figure 2.3. Zener Diode
         Zener Diode and         Determining Diode          Voltage Regulator
         Circuit Symbols        Parameters                   Circuit
Computer Simulation: Generate the diode charateristics on PSPICE. Use the circuit shown
below. Step through Id and plot Id vs Vd.




                                                                    +

                              Id                                        Vd




EE 345                         LAB # 2 - DIODE PROPERTIES                         PAGE 2

				
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