Lab report

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Experiment 5

DC Analysis of a Diode Circuit Using SPICE

Introduction

The purpose of this experiment is to gain practical experience with the mechanics of a

SPICE simulation, and to compare the results of the simulation with a hand-worked approximate

analysis, and laboratory measured results.

Pre-Lab

Analyze the circuit of Fig. 1 twice, once assuming the diode to be ideal, and then assuming

a constant-voltage-drop (CVD) of 0.7 V in the on state. Find the diode state, the diode voltage,

and the diode current. Bring these expected results to the lab. Equipment Needed

Equipment Needed

 1N4148 Small-signal silicon diode

 Current version of PSpice

 Normal lab equipment

Procedure

Turn on the PC and open the current version of PSpice. All simulations will be done using

a “DC” analysis. (This is also referred to as a “bias point” analysis.)

1. Simulate the circuit of Fig. 1 using a 1N4148 diode model from the component model

library. The results will appear in the output (*.OUT) file. Record the diode voltage and

current.

2. Simulate the circuit of Fig. 1 using the following diode model parameters: IS = 10-15 A

and N = 0.01. These can be entered in PSpice by editing the diode “instance model.”

Highlight the diode on the schematic and pick “Edit,” followed by “Model,” followed by

“Edit Instance Model.” This gives you access to the text file containing the diode model

Fig. 1 DC diode circuit.

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statements. The changes you make to the model will be local to your schematic only (they

will not change the library). Delete all existing model statements; enter the two model

statements1 given above. Record the diode voltage and current.

3. Assemble the circuit of Fig. 1 using a 1N4148 and measure the diode voltage and current

using a digital multimeter. Record the diode voltage and current.

Report:

Write a report that summarizes this experiment. Your report brief must include:

 Cover sheet.

 Objective - a short paragraph stating what the experiment is about.

 Procedure - a description of the process of conducting the experiment. It should not be a

step-by-step account, but rather an overview of what was done.

 Discussion - a complete discussion of the results of the experiment and the principals

involved. Include the outputs and also the screen captures as needed to support the

statements made in this section. Relegate extensive lists of raw data and detailed

computations to an appendix as appropriate.

 Conclusion - a summary of what you have learned from the experiment.

 Appendix - original raw data (initialed by the lab instructor) and details not placed in the

discussion section

The required results are the diode state (on or off), diode voltage, and diode current as given by

each of the following techniques:

(a) Hand calculation based on an ideal diode model.

(b) Hand calculation based on a CVD diode model.

(c) SPICE simulation based on a 1N4148 model.

(d) SPICE simulation based on N = 0.01 and IS = 10-15 A.

(e) Experimental measurement using a 1N4148 silicon diode.

(f) Comment on what happened when N was set to the unrealistically low value of 0.01

1 The format of the SPICE model statement should end up similar to the following:

.MODEL 1N4148 D( N=0.01 IS=1E-15 )