Solving circuit using Laplace Transforms

In summary, the conversation was about finding the voltage across an inductor in a circuit. The person started by solving for the current using differential equations and got an answer of iL(t) = E^(-5t) (-0.75 + 1.25E^(4t)). They then tried to solve it using Laplace transforms but did not get the same answer. They attached a pdf file with their approach and asked for help. Another person pointed out an error in their equation and the original person thanked them. They then mentioned trying to solve it by hand but have not been successful yet.
  • #1
perplexabot
Gold Member
329
5
Hi all. I need to find the voltage across the inductor. I begin by solving for the current in the inductor. I first solved a circuit using differential equations (with mathematica) and achieved an answer for current in inductor of: iL(t) = E^(-5 t) (-0.75 + 1.25 E^(4 t)

Later, I tried to solve the same circuit using Laplace transforms and was not able to yield the same answer (or anything close). The original circuit and my approach for solving the circuit using Laplace transforms is attached as a pdf file. In the pdf file, I am attempting to solve for the current in the inductor. I get an equation for iL(s), however, when I take the inverse laplace, the answer looks nothing like my diff-eq iL(t). Please let me know where I am going wrong. Hints are preferred over answers. Thank you.
 

Attachments

  • laplacetry.pdf
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  • #2
In your loop 2 equation the voltage drop across inductor should be (i2)sL.
 
  • #3
the_emi_guy said:
In your loop 2 equation the voltage drop across inductor should be (i2)sL.

WOW, you are so right. I can't believe I didn't see that. Thank you so much. I will give it another go. Hopefully I will not run into another error. Thanks again.
 
  • #4
Thanks the_emi_guy. That simple fix gave me the exact answer.
 
  • #5
You're welcome
 
  • #6
I am now trying to solve the circuit by hand using differential equations. I have attempted it twice and went over it many times but have not achieved the correct answer (i am close though). I may upload my attempt tonight and hopefully you (or someone else) may help me with that too.
 

Related to Solving circuit using Laplace Transforms

What is a Laplace Transform?

A Laplace Transform is a mathematical tool used to solve differential equations in engineering and physics. It converts a function of time into a function of complex frequency, making it easier to analyze and solve problems in the time domain.

How is a Laplace Transform used to solve circuits?

The Laplace Transform is used to solve circuits by converting the circuit's differential equations into algebraic equations in the frequency domain. This allows for easier analysis and calculation of circuit parameters such as voltage, current, and impedance.

What are the advantages of using Laplace Transforms in circuit analysis?

There are several advantages to using Laplace Transforms in circuit analysis. It allows for the use of algebraic equations instead of differential equations, making it easier to solve complex circuits. It also allows for the analysis of circuits with varying inputs, such as AC circuits, and provides a more intuitive understanding of circuit behavior.

Can Laplace Transforms be used for any type of circuit?

Yes, Laplace Transforms can be used for any type of circuit, including DC, AC, and mixed signal circuits. It can also be used for both linear and nonlinear circuits, although the calculations may be more complex for nonlinear circuits.

Are there any limitations to using Laplace Transforms for circuit analysis?

While Laplace Transforms are a powerful tool for circuit analysis, there are some limitations to consider. It may not be the most efficient method for simple circuits, and it may not be suitable for circuits with time-varying parameters. Additionally, the process of converting back to the time domain after using Laplace Transforms can be complex and time-consuming.

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