# DR circuits

Discussion in 'Homework Help' started by mihaipop11, Mar 24, 2013.

1. ### mihaipop11 Thread Starter New Member

Jan 12, 2013
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can you tell me if is any difference between these two circuits, because the VTC's are the same.

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2. ### WBahn Moderator

Mar 31, 2012
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What is the VTC that you are talking about?

Wouldn't you expect the voltage across a forward-biased diode to be different than the voltage across a resistor in series with a reverse-biased diode? Or are you using an ideal diode for your model.

But, in any event, yes, there is a difference between those two circuits.

3. ### mihaipop11 Thread Starter New Member

Jan 12, 2013
5
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VTC is the graphical representation of Vin(Vout), and yes, i'm using an ideal model

4. ### WBahn Moderator

Mar 31, 2012
18,093
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Well, if you are using an ideal model then the output voltages in both cases are always zero, but for very different reasons. I would argue that just because a particular voltage or current is the same between two circuits is no basis for declaring the two circuits equal. If so, then there would be no differences between any circuit powered by a 9V battery because the voltage across the battery is always the same in each circuit.

5. ### WBahn Moderator

Mar 31, 2012
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What does VTC stand for? About the only thing I can think of would be something like "voltage transfer characteristic".

6. ### mihaipop11 Thread Starter New Member

Jan 12, 2013
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this is what i'm talking about

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7. ### WBahn Moderator

Mar 31, 2012
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You've got a strange way of indicating voltage polarity. The typical way (but not only) is to use a + (and perhaps also a -) sign. When an arrow is used, I have always seen it point toward the more posiitve node. But, be that as it may, it is true that the diagrams for that one quantity are the same. But now plot the current in the circuit and you will see that those curves are different.

So while the two circuits can be said to be "equivalent" in terms of the specific voltage indicated, they are NOT the same and there is a significant difference between them.

8. ### mihaipop11 Thread Starter New Member

Jan 12, 2013
5
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ok, thanks, now i got it, but for example, i have to solve a problem, it goes like this: "Find the electrical circuit of the switching port to obtain the given VTC.", and the VTC is that graphical representation, bot circuits are correct, am i right?

9. ### WBahn Moderator

Mar 31, 2012
18,093
4,918
I would say yes.