# Thenovin's Equiv (Source Conversions)

Discussion in 'Homework Help' started by ajpik, Feb 13, 2014.

1. ### ajpik Thread Starter New Member

Feb 13, 2014
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I have a homework problem I'm working on, and a similar problem meant as an example.

I am having trouble on the homework, but the teacher used some techniques in the sample that I think would solve my problems. Edit: I'm still going to post the example because it directly relates to the problem but while typing this I answered someone of my own quesitons.

Really I think I am having trouble understand V_oc and I_sc, so I also included the excerpt from the book that attempts to explain those to me (I don't get it)

The attachments are annotated...

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2. ### ajpik Thread Starter New Member

Feb 13, 2014
15
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I attached some progress...
I just really don't know what to do about those A and B nodes. What is that thing?!?! Can I treat it like it's not there? Should I treat it like its shorted? I don't know when to do one or the other...

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3. ### shteii01 AAC Fanatic!

Feb 19, 2010
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There are two key concepts.

Concept 1.
Voltage is a field. Fields propagate through matter.

Concept 2.
Current is not a field. It needs medium to provide a path for it.

Moving on.

When you have open circuit, there is no path for the current, so all the voltage shows up at the open circuit. Maximum voltage, minimum current.

When you have short circuit, the short is the path of least resistance so all the current will take this path, and voltage across a short circuit is zero. Maximum current, minimum voltage.

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4. ### NguyenDon New Member

Feb 15, 2014
9
1
When finding the equivalent of a circuit from your reference nodes, you can imagine putting an unknown resistance in between those nodes. A resistance is effectively the ratio between voltage and current at those nodes. So in order to find the equivalent circuit, you must find the open circuit voltage at those nodes, V_oc, and the short circuit current, I_sc, and use the ratio to find the thevenin resistance. Then you may use either V_oc for a Thevenin or I_sc for a Norton.

Another possibility is that since we know that resistance is just the ratio between voltage and current, we may insert a test source, in this case lets say a voltage source, in-between the reference nodes and find the current through the source and vice versa. Using this method you can use an arbitrary source value since it will equivalently change the other value that you are seeking. In this case though, you must find the resistance of the test source and the test voltage/current in the active sign convention. This will only give you the resistance and you must find either V_oc or I_sc.

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5. ### ajpik Thread Starter New Member

Feb 13, 2014
15
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Suggestion to the moderators/admin:

Since this page is the FIRST RESULT when you google "Thenovin's Equivalent" or "Thenovin" (which is probably because I posted my question when 200 other students had the SAME homework and we're googling solutions), it might behoove you to capitalize on the traffic and directly link to your tutorial page about Thenovin's equivalent. Just sayin. Yes I realize I spelt it wrong. But it's something.

Last edited: Mar 7, 2014
6. ### WBahn Moderator

Mar 31, 2012
20,057
5,644
That it came up as the first result is mostly a result of you doing the search on the same computer (i.e., same browser) that you used to visit the site previously. Search engines use your browsing history to filter the searches to favor places you've been before. Sometimes that helpful and sometimes its a royal pain.