ELECTRICAL AND COMPUTER ENGINEERING
THE CITADEL
ELEC 313 Lab 2
Diode Characterization
OBJECTIVE:
to compare the voltage-and-current characteristic of a diode
against the Shockley equation model
EQUIPMENT:
diode -- 1N4002
resistors -- 470 Ω, 330 Ω, 680 Ω
resistive decade box -- Heathkit IN-3117 or General Radio Co. 1434-N
triple-output DC power supply -- Hewlett Packard E3631A
multi-meters -- Hewlett Packard 34401A, Fluke 8010A
INTRODUCTION:
The theoretical relationship between the voltage and current for a diode is the Shockley equation
 d

V
Id  Is  e T  1 .




V
In this lab experiment, you will measure the diode current and voltage using simple circuits
and compute the parameters Is (reverse saturation current) and VT (thermal voltage).
PRE-LAB:
Complete the following 3 steps in your laboratory notebook before arriving to perform Lab #2.
Diode Voltage vs. Current Characteristic
1.
Simulate the circuit of Figure 1 in PSpice. For the diode, use [“EVAL” library, “D1N4002” part].
Set Vs = 10 V, and set up a parameter sweep over the value of R :
a.
Place the “PARAM” part on your schematic (“SPECIAL” library). Edit the
“PARAM” part. Add a “New Property” (“Rx”). Give it a nominal value (“1k”).
b.
Give the component value of the resistor the same name, with curly braces (“{Rx}”).
c.
Set up a new “New Simulation Profile” with a “DC Sweep” over the “Global
Parameter” named “Rx”, using the following values: R = 200 , 500 , 1 k, 2 k,
5 k, 10 k, 20 k, 50 k, and 100 k. An example is shown in Figure 2.
Figure 1. Diode circuit schematic for resistor sweep.
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Figure 2. PSpice simulation for diode circuit resistor sweep.
Plot the diode voltage Vd and diode current Id against these resistor values.
Using cursors (“Trace”  “Cursor”  “Display”), make a table of values for Vd and Id vs. R .
Diode Circuit, DC Operating Point, Shunt Resistor
2.
Add shunt resistor R2 as shown to the circuit. Simulate this circuit for a single DC operating point.
(i.e. Change the “Analysis type” back to “Bias Point”.)
Figure 3. Diode circuit schematic, single DC bias point.
Keep Vs = 10 V, set R1 = 330 Ω, and set R2 = 680 Ω . Simulate the circuit and record Vd and Id .
3.
Simulate the circuit again without the diode. Record the voltage across the open circuit as VOC .
Figure 4. 1N4002 diode orientation.
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PROCEDURE:
Diode Voltage vs. Current Characteristic
1.
Ensure that you have the resistor (470 ) and diode (1N4002) to build the circuit of Figure 5.
Figure 5. Diode circuit to be breadboarded for resistor sweep.
a.
b.
2.
Measure the resistor, record this value, and compute percent error from nominal.
Ensure that the percent error is under 10% before proceeding.
Build the circuit of Figure 5. Use the HP E3631A –25-V/1-A supply for Vs .
Refer to Figure 4 for the proper orientation of the 1N4002 diode.
Use one multi-meter (HP 34401A) to measure DC voltage across the diode (Vd).
Use a second multi-meter (Fluke 8010A) to measure DC current through the diode (Id).
Set the ammeter to its lowest (200-A) scale.
3.
Vary Vs from –5 V to 0 V in 0.5-V steps, and record Vd and Id for each value of Vs .
4.
Switch Vs to the +25-V/1-A supply on the E3631A, vary Vs from 0 V to 5 V in 0.25-V steps,
and record Vd, and Id for each value of Vs . Adjust the scale of the ammeter as necessary.
5.
Vary Vs from 5.5 V to 10 V in 0.5-V steps, and record Vd, and Id for each value of Vs .
6.
Replace the 470- resistor with the decade resistance box, set to 200 . Set Vs to +10 V.
To prevent burning out the diode, the decade box must never be set below 50  .
7.
Measure and record Vd and Id at each of the following resistance settings:
R = 200 , 500 , 1 k, 2 k, 5 k, 10 k, 20 k, 50 k, and 100 k.
Adjust the scale of the ammeter as necessary to view small currents.
Be careful not to inadvertently set the resistance of the box to 0  while changing its value.
Diode Circuit, DC Operating Point, Shunt Resistor
8.
Ensure that you have the correct resistors (R1 = 330 Ω, R2 = 680 Ω) to build the circuit of Figure 3.
a.
b.
9.
Measure both resistors, record their values, and compute percent error from nominal.
Ensure that no percent error is above 10% before proceeding.
Build the circuit of Figure 3 with Vs = 10 V, R1 = 330 Ω, R2 = 680 Ω . Measure Vd and Id .
10. Remove the diode and measure the voltage across the nodes where it had been connected, VOC .
11. Complete the Data Analysis section before leaving the lab.
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DATA ANALYSIS:
1.
Using Excel or Matlab, plot Id (vertical) vs. Vd (horizontal) from Procedure steps 3–5.
Label your axes appropriately.
2.
Plot the natural logarithm of the current ln{Id} vs. Vd for Vd > 0 V .
The resulting plot should be a straight line whose slope is equal to 1/VT .
3.
From this generated plot, estimate and record VT .
Pick two representative current values along the straight line, and calculate VT from
1

ln ( I 2 )  ln  I 1 
V 2  V1
VT
4.
Calculate the saturation current Is by solving Shockley’s equation (in the Introduction)
for a measured (Vd, Id) pair and using your calculated VT .
5.
Compute percent error for Vd and Id (vs. simulation) recorded for the shunt-resistor circuit.
QUESTIONS:
1.
Does your measured data set (Vd, Id) match the Shockley diode model? Why or why not?
2.
What is the meaning of the thermal voltage, VT ?
Is your calculated VT reasonable? Why or why not?
3.
What is the meaning of the saturation current, Is ?
Is your calculated Is reasonable? Why or why not?
4.
Does your measured sweep of resistor values match your simulated sweep? Why or why not?
5.
Does your measured shunt-resistor circuit (Vd , Id) match your simulation? Why or why not?
6.
For the shunt-resistor circuit, why does Vd not match VOC ?
LAB REPORT:
Complete your lab report in the format requested by your instructor. It must contain the following items:
1. Cover page -- including the lab number, title, and the date that the experiment was performed
All participating students must list their names on and sign the Cover page.
2. Objective -- a paraphrase of the purpose of the experiment
3. Equipment -- a list of all breadboarded components and instruments used for measurement
All model numbers (of components & instruments) must be listed.
4. Test configuration -- drawings of all relevant circuits and test configurations
Component values and chips must be labeled on the relevant schematics.
5. Procedure -- a summary of the test procedure
The entire report must be written in the passive voice and in the present/past tense.
6. Theoretical results -- tables/figures including all pre-lab simulations, derivations, & computations
7. Measured results & Data analysis -- tables/figures/plots including all data recorded in the lab
8. Comparison -- tables/figures, Theoretical vs. Measured values, with percent error
Results sections must discuss the significance of the data before the Conclusions.
9. Discussion -- any additional relevant analysis/discussion to be included before the Conclusions,
including answers to Questions asked in the lab procedure
10. Conclusions -- a brief statement of how the lab Objective was accomplished
The Conclusions section is not used to discuss data; it is only used to summarize.
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