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tdabboud
Group Title
Transient analysis problem
http://imageshack.us/photo/myimages/827/99437379.jpg/
I need to find the value for C, where the voltage across the capacitor will not exceed a) 200V, b) 20V and c) 2V.
I have done it on pspice and got answers but I want to understand how to do the problem by hand. Your help is much appreciated
 3 years ago
 3 years ago
tdabboud Group Title
Transient analysis problem http://imageshack.us/photo/myimages/827/99437379.jpg/ I need to find the value for C, where the voltage across the capacitor will not exceed a) 200V, b) 20V and c) 2V. I have done it on pspice and got answers but I want to understand how to do the problem by hand. Your help is much appreciated
 3 years ago
 3 years ago

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imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
no worry, ee here
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
thank god, I have been working on this problem for 3 hours now
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
What I think I have come to is that i need to do an analysis for when t=0+ and t=100u as well as when t=100u+ and t=infinity
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
Let me see , if I have that correctly There are two switches , one open at t=100 us other close at t=0 ?
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
yes that is correct
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
It's a DC , right?
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
i dont think that would matter though. I know when you have dc, the capacitor will open but i dont think it will in this case since the voltage across that resistor is the same as the capacitor
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
Well we have to consider phase lag if it is AC
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
okay that makes sense
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
This is DC Parellel RC circuit First time for me
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
I got some Differential equations that might work, hopefully
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
Yeah same here..all of the examples are usually series RC and parallel RL. I think thats why it is so challenging. I made an attempt the first time to change the source and resistor into a non ideal current source. then find the current through the resistor. From that I feel that you may be able to get the right voltages but its very confusing. Another thing is I think it is two transient problems in one. one being 0<t<100us and the second being t>100us
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
Did you get 9.91 uF using PSPICE?
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
for 200 V
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
well for 200 V you could have any value capacitance because the voltage across the resistor will peak at 150 V.. so you will never have a value of capacitance that can make it go higher
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
But isn't capacitor connected in parellel across the 300 V source?
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
dw:1322624761701:dw
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
the capacitor is parallel with the resistor....which is in series with the next resistor...which is in series with the voltage source
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
oh, I was looking at it wrong
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
so at t=0, the 300V will drop to 150V after the first 2 ohm resistor, since the capacitor and resistor are in parallel they will both have a voltage drop of 150 V. So this is the max voltage that can be across the capacitor no matter what the value. once 100us comes the capacitor stops charging and then discharges as you can see from my sloppy grapg
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
So , I am assuming at t=0 , \[I_c= infintiy\]
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
that cant be true
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
at t=0 the current through the resistor is not infinity so the current through the capacitor cannot be 0
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
sorry cannot be infinity
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
oh, it should start at 75 amps?
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
i do not think so. I am not sure how you got that. are you converting to NICS?
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
I don't know what to do. Try www.physicsforums.com , if you haven't already; They may be able to help you . Good luck
 3 years ago

tdabboud Group TitleBest ResponseYou've already chosen the best response.0
ok thanks I will try that! I too am an EE, junior, goodluck with your studies
 3 years ago

imranmeah91 Group TitleBest ResponseYou've already chosen the best response.0
I am Sophomore,
 3 years ago
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