Question

Transient analysis problem

http://imageshack.us/photo/my-images/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

Answer 1

no worry, ee here

Answer 2

thank god, I have been working on this problem for 3 hours now

Answer 3

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-

Answer 4

Let me see , if I have that correctly

There are two switches , one open at t=100 us other close at t=0 ?

Answer 5

yes that is correct

Answer 6

It's a DC , right?

Answer 7

yes dc

Answer 8

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

Answer 9

Well we have to consider phase lag if it is AC

Answer 10

okay that makes sense

Answer 11

This is DC Parellel RC circuit

First time for me

Answer 12

I got some Differential equations that might work, hopefully

Answer 13

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

Answer 14

Did you get 9.91 uF using PSPICE?

Answer 15

for 200 V

Answer 16

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

Answer 17

But isn't capacitor connected in parellel across the 300 V source?