# Choose device values given Vin and Vout

Discussion in 'Homework Help' started by applefat, Oct 12, 2007.

1. ### applefat Thread Starter Member

Oct 12, 2007
10
0
Hello;

I've really been pulling my hair on this AC analysis design question, though I assure you I have put in a significant amount of effort before coming here. The attached circuit is VERY simple, so I clearly must be making the same mistake over and over.

What I've tried to do mainly is approach it like a reverse thevenin-equivalent problem, but instead of having to find Vo, you already have it. Then you choose a value for one of the resistors and go from there, using impedance, but I absolutely cannot get a reasonable answer (that is, POSITIVE resistances and REAL capacitance!)

I've tried nodal, thevenin, and mesh (simultaneous equations), but the latter especially went nowhere fast.

Please, anyone who can point me in a good direction for properly approaching this problem will earn a huge amount of appreciation!!!

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2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
Is the voltage out 25 volts, or 2.5?

3. ### applefat Thread Starter Member

Oct 12, 2007
10
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2.5, sorry. The part after the @ is the phase btw, if that wasn't completely clear.

4. ### techroomt Senior Member

May 19, 2004
198
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are you positive about that phase number of 104 deg? i did not think reactance could cause any more then 90 deg phase shift, and even then it is only ideal.

5. ### applefat Thread Starter Member

Oct 12, 2007
10
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Yep, it's what the assignment sheet tells me anyway, and while it could be an error, he isn't really known for them...

The functions:
Vi = 12cos(1000t) V
Vo = 2.5cos(1000t+104) V

6. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
That's a head-scratcher - I thought RC combos only approached 90 deg phase shift. I'm glad I never had to mess with those school problems.

7. ### Distort10n Active Member

Dec 25, 2006
429
1
You sure this is not a trick question? You cannot have anymore than 90 degrees of phase lag with a capacitor.

8. ### applefat Thread Starter Member

Oct 12, 2007
10
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Hmmm, interesting insight... I will email the instructor, thanks for the clue guys.

9. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,281
326
If you make R1 a negative resistor it can be done.