Transient Analysis of RL and RC Circuits Using LTSpice®
Mechanical Engineering (BEng.) Degree
MEC1151 – Electrical Circuits and Analysis
27/10/22
School of Engineering
University of Glasgow
Date of Completion: 24/11/2022
Table of Contents
,Abstract.................................................................................................................................................3
Introduction...........................................................................................................................................3
1.1 LTSpice.........................................................................................................................................3
Theoretical Background.........................................................................................................................3
2.1 RL Circuit......................................................................................................................................4
2.2 RC Circuit......................................................................................................................................4
Experiment Procedures..........................................................................................................................5
3.1 Transient Response of a Series RL Circuit.....................................................................................5
3.2 Transient Response of a Series RC Circuit....................................................................................5
Experimental Results and Analysis.........................................................................................................6
Discussion............................................................................................................................................10
5.1 Experimental Discussion............................................................................................................10
5.2 Experimental Questions.............................................................................................................10
Conclusion...........................................................................................................................................11
References...........................................................................................................................................12
Appendix..............................................................................................................................................13
, Abstract
The objective of this report is to evaluate two circuits and their transient responses. For each circuit,
we will need to determine the response analytically through calculations and simulate the response
using LTSpice.
For the RL and RC circuits transient analysis, calculations were performed, and computer simulations
were performed. The theoretical and simulated results returned nearly the same.
Introduction
The purpose of this experiment is to study transients and time constants in simple RL and RC circuits.
For the first part of the experiment, RL transient response, using LTSpice, a voltage source and a
resistor is connected in series with an inductor forming the RL series circuit. The voltage source is
also modified to pulse and configured with the given details.
For the second part of the experiment, RC transient response, using LTSpice, a voltage source and a
resistor is connected in series with a capacitor forming an RC circuit. Then the voltage source is
adjusted by setting it to pulse function.
1.1 LTSpice
LTSpice is a free circuit simulator from the manufacturer Analog Devices that uses a mixture of Spice
command and circuit diagrams with a sizable library of passive and active components. The software
also allows sub-circuits and Hierarchical circuits of any size, even from third-party sources to add
components that are not currently available in the library. Furthermore, this tool is useful for testing
out ideas that often use high current which requires plenty of safety factors when testing.
Theoretical Background
An inductor is an electrical element which stores energy in the form of a magnetic field and a
capacitor is an electrical element which stores energy in the form of an electric field. When charged
by a power source, an inductor or capacitor can function a temporary power source itself, until its
charge is depleted. The action of charging an inductor or capacitor is known as step response.
Once the power source is removed from the circuit, the charged inductor or capacitor will discharge
itself into any connected resistance. The action of discharging an inductor or capacitor is known as
natural response.
In transient analysis, elements in a circuit have time varying responses rather than constant values.
These responses are modelled as differential equations and are functions of time. The rate at which
an element response changes according to time depends on a time constant.
Mechanical Engineering (BEng.) Degree
MEC1151 – Electrical Circuits and Analysis
27/10/22
School of Engineering
University of Glasgow
Date of Completion: 24/11/2022
Table of Contents
,Abstract.................................................................................................................................................3
Introduction...........................................................................................................................................3
1.1 LTSpice.........................................................................................................................................3
Theoretical Background.........................................................................................................................3
2.1 RL Circuit......................................................................................................................................4
2.2 RC Circuit......................................................................................................................................4
Experiment Procedures..........................................................................................................................5
3.1 Transient Response of a Series RL Circuit.....................................................................................5
3.2 Transient Response of a Series RC Circuit....................................................................................5
Experimental Results and Analysis.........................................................................................................6
Discussion............................................................................................................................................10
5.1 Experimental Discussion............................................................................................................10
5.2 Experimental Questions.............................................................................................................10
Conclusion...........................................................................................................................................11
References...........................................................................................................................................12
Appendix..............................................................................................................................................13
, Abstract
The objective of this report is to evaluate two circuits and their transient responses. For each circuit,
we will need to determine the response analytically through calculations and simulate the response
using LTSpice.
For the RL and RC circuits transient analysis, calculations were performed, and computer simulations
were performed. The theoretical and simulated results returned nearly the same.
Introduction
The purpose of this experiment is to study transients and time constants in simple RL and RC circuits.
For the first part of the experiment, RL transient response, using LTSpice, a voltage source and a
resistor is connected in series with an inductor forming the RL series circuit. The voltage source is
also modified to pulse and configured with the given details.
For the second part of the experiment, RC transient response, using LTSpice, a voltage source and a
resistor is connected in series with a capacitor forming an RC circuit. Then the voltage source is
adjusted by setting it to pulse function.
1.1 LTSpice
LTSpice is a free circuit simulator from the manufacturer Analog Devices that uses a mixture of Spice
command and circuit diagrams with a sizable library of passive and active components. The software
also allows sub-circuits and Hierarchical circuits of any size, even from third-party sources to add
components that are not currently available in the library. Furthermore, this tool is useful for testing
out ideas that often use high current which requires plenty of safety factors when testing.
Theoretical Background
An inductor is an electrical element which stores energy in the form of a magnetic field and a
capacitor is an electrical element which stores energy in the form of an electric field. When charged
by a power source, an inductor or capacitor can function a temporary power source itself, until its
charge is depleted. The action of charging an inductor or capacitor is known as step response.
Once the power source is removed from the circuit, the charged inductor or capacitor will discharge
itself into any connected resistance. The action of discharging an inductor or capacitor is known as
natural response.
In transient analysis, elements in a circuit have time varying responses rather than constant values.
These responses are modelled as differential equations and are functions of time. The rate at which
an element response changes according to time depends on a time constant.
