DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 1

EE 221 L CIRCUIT II

LABORATORY 1: DC CIRCUITS & LTSPICE

DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING

UNIVERSITY OF NEVADA, LAS VEGAS

OBJECTIVE

Better understand circuit laws, theorems and analysis approaches, e.g. KCL, KVL, node &

mesh analysis, superposition, Thevenin’s Theorem & Norton’s Theorem, Δ-Y convertion, etc.

Learn to use LTspice for circuit simulations, measuring voltage at each node and current

through each component.

COMPONENTS & EQUIPMENT

Computer with Windows OS

LTspice software

BACKGROUND

SPICE (Simulation Program with Integrated Circuit Emphasis) is a general-purpose, open

source analog electronic circuit simulator. It is a program used in integrated circuit and board-level

design to check the integrity of circuit designs and to predict circuit behavior.

LTspice is a high-performance SPICE simulator, schematic capture and waveform viewer with

enhancements and models for easing the simulation of various circuits. Current version included

in this download are LTspice, Macro Models for majority of Linear Technology's switching

regulators, over 200 op amp models, as well as resistors, transistors and MOSFET models.

Kirchhoff's circuit laws are two equalities that deal with the current (KCL) and potential

difference (commonly known as voltage, KVL) in the lumped element model of electrical

circuits. “±” can be used to represent the directions of currents and voltages.

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DC is the unidirectional flow of electric charge. The DC solution of an electric circuit is the

solution where all voltages and currents are constant, zero-frequency, or slowly varying local mean

value of a voltage or current. A battery is a good example of a DC power supply. Some power

adapter (e.g. your laptop power adapter, desktop power supply, etc.) can convert AC power, which

will be examined in future labs, into DC power.

Electrical Circuit Rules &

Elements

Graphic Description (I-V Plot)

KCL

I1

I2

I3

I4

I5

KVL

Ideal DC Voltage Supply

𝑉 = 𝑉0

𝐴 ∈ 𝑅

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Ideal DC Current Supply

𝐴 = 𝐴0

𝑉 ∈ 𝑅

Non-Ideal DC Voltage and

Current Supply

Resistor

𝑉 = 𝐼𝑅

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Voltage divider

Thevenin Equivalent Theorem

Δ − 𝑌 Conversion

𝑅1 =𝑅𝑏𝑅𝑐

𝑅𝑎 + 𝑅𝑏 + 𝑅𝑐

𝑅2 =𝑅𝑐𝑅𝑎

𝑅𝑎 + 𝑅𝑏 + 𝑅𝑐

𝑅3 =𝑅𝑎𝑅𝑏

𝑅𝑎 + 𝑅𝑏 + 𝑅𝑐

𝑅𝑎 =𝑅1𝑅2 + 𝑅2𝑅3 + 𝑅3𝑅1

𝑅1

𝑅𝑏 =𝑅1𝑅2 + 𝑅2𝑅3 + 𝑅3𝑅1

𝑅2

𝑅𝑐 =𝑅1𝑅2 + 𝑅2𝑅3 + 𝑅3𝑅1

𝑅3

Two forms of same network (a) Y (b) T

Two forms of same network (a) Δ (b) Π

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LAB DELIVERIES

PRELAB:

1. Read:

https://en.wikipedia.org/wiki/Electronic_circuit_simulation

https://en.wikipedia.org/wiki/SPICE

2. Go through “Simulations Step-by-Step with Schematic Files” starting from Page 9

of this manual.

LAB EXPERIMENTS:

1. Simulate the following Circuit 1 (1) and (2) for 1ms, respectively, and measure the

output voltage and current through each resistor.

• Fill in the table, and show your hand calculation process.

• Compare the hand calculation and LTspice simulation, do they meet KCL and KVL?

• Compare Circuit 1 (1) and (2), what can you conclude with Thevenin’s/Norton’s Theorem?

Circuit 1 (1) Circuit 1 (2)

𝑉𝑜𝑢𝑡 (V) 𝑖𝑅1 (mA) 𝑖𝑅2 (mA) 𝑖𝑅3 (mA)

Circuit 1 (1) Hand Calculation

LTspice Simulation

Circuit 1 (2) Hand Calculation

LTspice Simulation

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2. Simulate the following circuit for 1ms.

• Does it include one or more Δ or Y circuit? Why?

• Hand calculate 𝑅𝑒𝑞, and compare 10/𝑖0 − 5, where 𝑖0 is measured by LTspice.

Circuit 2

3. Simulate the following circuit for 1ms, and write down 𝑰𝟎.

• Use Δ − 𝑌 conversion to hand calculate 𝑅𝑒𝑞. Show process.

• Run LTspice simulation, and compare 12/𝐼0 with the 𝑅𝑒𝑞 that you have calculated.

Circuit 3

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4. Simulate the following circuit for 1ms, and write down the voltage at each node and

the current through each resistor.

• Hand calculate the voltages at each node and current through each resistor. Show the process.

• Compare the results if

1) only applying voltage source, i.e. no current source

2) only applying current source, i.e. no voltage source

3) applying both current and voltage sources.

• What can you conclude regarding superposition law?

Circuit 4

Circuit 4 V1 (V) V2 (V) I (R1) (mA) I (R2) (mA) I (R3) (mA) I (R4) (mA)

1) Calculation

LTspice

2) Calculation

LTspice

3) Calculation

LTspice

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POSTLAB REPORT:

Include the following elements in the report document: Section Element

1 Theory of operation Include a brief description of every element and phenomenon that appear during the experiments.

2 Prelab report

None

3

Results of the experiments

Experiments Experiment Results

1 Screenshots of LTspice demo, as required in Prelab

2 Experiment 1 simulation results and hand calculation process.

3 Experiment 2 simulation results and hand calculation process.

4 Experiment 3 simulation results and hand calculation process.

5 Experiment 4 simulation results and hand calculation process.

4

Answer the questions

Questions Questions

1 Why do we use SPICE for simulations before implementing real circuits?

2 Answer questions in Experiment 1~4 marked in red.

5 Conclusions Write down your conclusions, things learned, problems encountered during the lab and how they were

solved, etc.

6

Images Paste images (e.g. scratches, drafts, screenshots, photos, etc.) in Postlab report document (only .docx,

.doc or .pdf format is accepted). If the sizes of images are too large, convert them to jpg/jpeg format

first, and then paste them in the document.

Attachments (If needed) Zip your projects. Send through WebCampus as attachments, or provide link to the zip file on Google

Drive / Dropbox, etc.

REFERENCES & ACKNOWLEDGEMENT

1. C. K. Alexander and M. Sadiku, “Fundamentals of Electric Circuits”, 4th Ed。

2. http://www.linear.com/designtools/software/

I appreciate the help from faculty members and TAs during the composing of this instruction

manual. I would also thank students who provide valuable feedback so that we can offer better

high education to the students.

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Simulation Step-by-Step with Schematic Files

LTspice can run simulations on either schematic files or coded netlist files. Both methods are quite

similar, and only simulations with schematic files are introduced in detail here.

Step 1: Install LTspice and open the software (Click No if requested update).

Current version: LTspice XVII.

Step 2: Create a new schematic, or open an existing schematic file.

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Step 3: Add/Modify/Delete electrical components into the schematic.

• Shortcut keys and buttons; zoom in/out or rotate components if needed. Also available to view in

“Control Panel”.

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Step 4: Add components from the library, and place them at proper positions.

• Components will be placed where you left click the mouse, until you press “ESC” to stop placing

that component.

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Step 5: Add wires (click and release) to connect all components; fulfill the circuit/schematic.

Step 6: Right click on the components, and change their values.

Step 7: “Run” the simulation.

• Fill in the simulation duration (stop time) and precision (timestep). Simulation command will be

generated automatically. You can modify the command after you learn more about LTspice or other

SPICE.

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• Click “OK” to run. The window arrangement of the trace panel (Draft1.raw) and the schematic

panel (Draft1.asc) can be adjusted.

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• Color of trace panel can be adjusted in “Tools”, “Color Panels”, “WaveForm” tab, “background”

in pulldown menu.

Step 8: View the output

1) Left click to activate (bring front) the schematic panel. Place the cursor on the node/wire (voltage)

or the element (current), and left click to probe and display the measured values.

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2) Right click on the trace panel, select “Add Traces”, and left click on the signals you want to see.

Click “OK” to display.