Title: RLC Circuits (SecondOrder Circuits) Post by: Pis on October 07, 2009, 05:39:41 pm I using LTSPice and PSpice to do a simulation eith RLC circuits. This is my first time using LTSpice for rlc simulation. The problem is, I don't know to handle RLC circuits using LTSpice. PSpice, i haven't try yet.
(http://www.phy.ntnu.edu.tw/ntnujava/img/4846_1.jpg) This is the circuit. (http://www.phy.ntnu.edu.tw/ntnujava/img/4846_2.jpg) This is my drawing using LTSPice I already run the simulation, but, I think, my setting is wrong, for RLC circuits, is different, i cannot directly just input the dc value right?....i confused, please help me...anyone... 1) I want to find V(t) and Vr(t) for t>0 for R=10, R=20, and R=30 Ohm...so i want to verify my answer with this simulation using LTspice... 2) Then i want determine v(t) for t=0.8s... Thank you, this is my first time, using ltspice for rlc circuits... Title: Re: RLC Circuits (SecondOrder Circuits) Post by: FuKwun Hwang on October 08, 2009, 04:48:12 pm Your problem can be solved analytically.
The switch between capacitor and 2Ω opened at t=0, it means that the capacitor is charged to 12V*2/3=8V at t=0. The problem reduced to RLC circuit with initial conditions: t=0; I=0, Vc=8V, V_{R}=0V, V_{L}=2V (V_{L}=10VcV_{R} ) The differential equation need to be solved is $10=L \frac{dI}{dt}+IR+\frac{1}{C}\int I dt$ or $L\frac{d^Q}{dt^2}+I\frac{dQ}{dt}+\frac{Q}{c}=0$ The solution is similar to a spring with constant k, attached with mass m and damping constant b. $m\frac{d^2x}{dt^2}+b\frac{dx}{dt}+kx=0$ The analytical solution can be found in standard textbook. You are also welcomed to check out RLC circuit simulation (DC Voltage source) (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=30.0) to find out the simulated solution. Title: Re: RLC Circuits (SecondOrder Circuits) Post by: Pis on October 09, 2009, 11:46:45 pm Your problem can be solved analytically. The switch between capacitor and 2Ω opened at t=0, it means that the capacitor is charged to 12V*2/3=8V at t=0. The problem reduced to RLC circuit with initial conditions: t=0; I=0, Vc=8V, V_{R}=0V, V_{L}=2V (V_{L}=10VcV_{R} ) The differential equation need to be solved is $10=L \frac{dI}{dt}+IR+\frac{1}{C}\int I dt$ or $L\frac{d^Q}{dt^2}+I\frac{dQ}{dt}+\frac{Q}{c}=0$ The solution is similar to a spring with constant k, attached with mass m and damping constant b. $m\frac{d^2x}{dt^2}+b\frac{dx}{dt}+kx=0$ The analytical solution can be found in standard textbook. You are also welcomed to check out RLC circuit simulation (DC Voltage source) (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=30.0) to find out the simulated solution. Oh, ok, thanks, this problem already solved. I must put in the initial condition for capacitor, 8V. So my circuit will become like this: (http://img2.pict.com/e7/67/54/1738217/0/1.jpg) I simplified it. IC=Initial condition. Then, settings: (http://img2.pict.com/d9/91/de/1738218/0/2.jpg) Tick "Skip initial operating..." Finally, become like this: (http://img2.pict.com/65/49/43/1738219/0/3.jpg) Then I just run the simulation for the graph. Must put the equation also for V(t) and Vr(t)... Already solved, thanks! ;D Title: Re: RLC Circuits (SecondOrder Circuits) Post by: FuKwun Hwang on October 10, 2009, 09:31:03 am It is great that you can solve it by yourself! :D
