• Support PF! Buy your school textbooks, materials and every day products Here!

Help with KCL/Thevenin Problem - Urgently Needed

  • Thread starter Fjolvar
  • Start date
  • #1
156
0
I tried solving this problem using KCL, but V1 keeps adding up to zero for my second set of equations. I'm not sure what I'm doing wrong. Any help is much appreciated.

1. Homework Statement

I need to find the Thevenin equivalent circuit. I chose to find the Isc and the Voc by using KCL, since I don't see another way.

o72d0w.jpg


Homework Equations


KCL

The Attempt at a Solution


[/B]
You can see for equation 2, my V1 equals zero due to the dependent current source relation. Not sure how to get around this.

2vltrf5.jpg
 

Answers and Replies

  • #2
NascentOxygen
Staff Emeritus
Science Advisor
9,244
1,071
Right at the start you write is = 8v/2Ω

Why do you say this?
 
  • #3
156
0
Right at the start you write is = 8v/2Ω

Why do you say this?
My mistake. That should read (v1-8)/2.

I'm still stuck on the second equation however since v1 equals zero. Am I missing something obvious here?
 
  • #4
CWatters
Science Advisor
Homework Helper
Gold Member
10,529
2,295
My mistake. That should read (v1-8)/2.
I don't think that's right either.

Edit: Do you mean "Is = (v1-8)/2" or that term in equation should be (v1-8)/2 ? The latter is correct.
 
Last edited:
  • #5
156
0
I don't think that's right either.

Edit: Do you mean "Is = (v1-8)/2" or that term in equation should be (v1-8)/2
That's for the term in the first KCL equation. But V1 in the second equation equals zero which has me stuck. I can't set up my equations to find any of the unknowns.
 
  • #6
CWatters
Science Advisor
Homework Helper
Gold Member
10,529
2,295
I think you mean V2 = 0 not V1.
 
  • #7
156
0
I think you mean V2 = 0 not V1.
I mean (-1/20 + 1/20) zeroes out V1 at node 2, since the dependent source is equal to 0.05V1
 
  • #8
NascentOxygen
Staff Emeritus
Science Advisor
9,244
1,071
You can see for equation 2, my V1 equals zero due to the dependent current source relation. Not sure how to get around this.
I see the problem. They cunningly have the current source always draining the entire current sourced through the 20Ω.

An alternative method to determine the impedance at ab is to apply a test voltage across ab and calculate how much current is drawn from that source. I guess that means the Thévenin equivalent will then be a simple resistance.
 
  • #9
156
0
I see the problem. They cunningly have the current source always draining the entire current sourced through the 20Ω.

An alternative method to determine the impedance at ab is to apply a test voltage across ab and calculate how much current is drawn from that source. I guess that means the Thévenin equivalent will then be a simple resistance.
I'm not quite sure what you mean :/
 
  • #10
CWatters
Science Advisor
Homework Helper
Gold Member
10,529
2,295
If V2=0 you can connect node V2 to 0V with a wire. Try that and redraw the left hand side of the circuit.
 
  • #11
NascentOxygen
Staff Emeritus
Science Advisor
9,244
1,071
I'm not quite sure what you mean :/
Connect a 1v supply to the right-hand side of a-b and calculate the current that flows into a-b from that 1v source.
 

Related Threads on Help with KCL/Thevenin Problem - Urgently Needed

  • Last Post
Replies
9
Views
4K
  • Last Post
Replies
13
Views
743
Replies
16
Views
1K
Replies
8
Views
2K
Replies
14
Views
4K
Replies
3
Views
941
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
2
Views
379
  • Last Post
Replies
6
Views
2K
Top