# Multiple Diodes Problem

Discussion in 'Homework Help' started by SilverKing, Apr 26, 2016.

1. ### SilverKing Thread Starter Member

Feb 2, 2014
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Hi everyone,

I am stuck with the following problem:
If V(1)=10 V and V(0)=5 V, and the voltage threshold for all diodes is 0.6 V. Determine the current through every diode and the output voltage Vo if V1=V4= 5V and V2=V3=10 V.

I know that the basic idea to determine whether the diode is on or off is by assuming one state and then confirm it. The thing is I could do that with two or three diodes at most. but I know another to determine its state which is done by determining the voltages on both the anode and the cathode separately. And that I what I was going, but I couldn't determine some voltages like V[SUB]A[/SUB] and V[SUB]B[/SUB] in the following figure:

Any help?

2. ### shteii01 AAC Fanatic!

Feb 19, 2010
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I don't see V(1) and V(0) on any of the circuits. What do they represent? Or are they just extra information, placed there to confuse?

3. ### SLK001 Well-Known Member

Nov 29, 2011
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It's V1 and V0. V1 is in the upper left corner and V0 about in the center, under the 15k resistor.

4. ### GopherT AAC Fanatic!

Nov 23, 2012
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Is any current going to flow from the 5V source into the 10V source? I think not. This exercise is just teaching that diodes limit current flow to one direction. Or block flow if anode is not higher voltage than cathode.

5. ### WBahn Moderator

Mar 31, 2012
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Shteii01 is correct. The information given is contradictory and/or incomplete.

The problem states that V(1) = 10 V and V(0) = 5 V. It then asks you to determine Vo if V1 = V4 = 5V. So that indicates that V(1) is NOT the same as V1 and that V(0) is NOT the same as V0. But while V1 and V2 are clearly labeled on the diagram, V(1) and V(0) are no where to be found.

6. ### GopherT AAC Fanatic!

Nov 23, 2012
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The notation is written by the OP (not copied from the image of the publisher or professor) and he doesn't seem bothered by V1 vs V(1) so I would assume they are the same. Even if it was from the publisher, as a teacher, I would crap all over any student who came to class without anything complete if they said, "v1 is on the image but I couldn't find V(1) or V(0)."

More importantly, if an employee came to me and said, "the customer sent this over but I can't find V(1) anywhere so I assumed they were idiots and I stopped working on it", I would crap all over them too.

7. ### WBahn Moderator

Mar 31, 2012
18,087
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I don't have any problem believing that you would crap all over someone who came to you and said, "The diagram has V1 on it but no V(1), however the description that came with it says that V(1) = 10 V but that V1 = 5V. Also, the diagram has V0 on it but not V(0) and, again, the description says that V(0) is 5 V but asks us to find Vo."

Fine. Since you would assume they are the same, then what is V1? Is it 10 V or is it 5 V. The problem says both (if you want to blindly assume that they are the same).

But I guess that doesn't matter since the problem asks you to find V0 right after stating that V0 = 5 V.

So would you just expect your employee to just respond Vo = 5 V and bill the customer for services rendered?

8. ### GopherT AAC Fanatic!

Nov 23, 2012
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If that is the only option you have, I'd crap all over you too! Determine what's missing or unclear and then Pick up the phone and find the missing information. People that sit on their thumbs and claim they can't move forward drive me crazy.

9. ### WBahn Moderator

Mar 31, 2012
18,087
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Who is sitting on their thumbs and claiming they can't move forward?

Did I not, very, very explicitly not only point out that the information given is contradictory and/or incomplete, but described explicitly exactly what was contradictory and/or incomplete?

Did you expect ME to somehow "pick up the phone" and find the information? How on earth was I supposed to do that? Perhaps I should use my crystal ball to peer into the TS's mind to find out where the problem came from and who wrote it so that I can peer into THEIR mind to resolve the issue for the TS?

Or were you driven crazy because the TS didn't come back in less than eight minutes after being informed about the issue (because, of course, it's completely inconceivable that it might take them longer than that to even SEE the post informing them of the information that is contradictory and/or missing)?

Or perhaps you think that everyone should just ignore contradictory and/or missing information, choose their own values regardless of whether they are in any way consistent with the information given, give answers to some problem that may or may not have any relation to the problem given, and then get all upset and take pride in "crapping all over someone" when it's made evident they failed to spot that the original problem contains contradictory and/or missing information (since it might make them look like a buffoon who sloppily made unreasonable assumptions without giving it the slightest thought).

10. ### SilverKing Thread Starter Member

Feb 2, 2014
72
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This is what I've done:

Is it alright?

11. ### WBahn Moderator

Mar 31, 2012
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I can't read your scans, particularly the second one. You need to scan with a higher resolution (or not reduce the resolution so much). If the file turns out to be much over 100 kB, just attach it to the post (instead of inserting it within the post).

Have you resolved the V(1) vs. V1 issue?

It might help if you include an actual scan of the problem statement and the original diagram so that we can see the source material to help you resolve it.

12. ### GopherT AAC Fanatic!

Nov 23, 2012
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Whoa, trigger! When did this become about WBahn? Um, insecure much?

13. ### WBahn Moderator

Mar 31, 2012
18,087
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You tried to make it that way. Don't even pretend otherwise.

Feb 2, 2014
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15. ### SilverKing Thread Starter Member

Feb 2, 2014
72
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Sorry for not clarifying enough, I didn't have access to the internet in the past few hours. V(1) means the logic high output voltage, and vice versa for V(0). I hope I didn't cause any trouble by doing that. ^^"

16. ### WBahn Moderator

Mar 31, 2012
18,087
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Thanks for the clarification.

So if I understand you correctly, we can actually ignore the first part of the statement where it talks about V(1) and V(0) since the actual voltages at the four inputs are given explicitly later on.

Or, said another way, the problem could have equivalently been stated:

If V(HI)=10 V, V(LO)=5 V, and the voltage threshold for all diodes is 0.6 V.

Determine the current through every diode and the output voltage Vo if V1 = V4 = LO and V2 = V3 = HI.

Mar 31, 2012
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Nov 23, 2012
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19. ### SilverKing Thread Starter Member

Feb 2, 2014
72
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WBahn

Yes, we can ignore them. And thank for your time. I'm waiting for you.

GopherT

Thanks

20. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
You did well. Your final answer should be 1.63 mA (1.88 mA - 0.25 mA). It looks like you have either 1.60 mA or 1.68 mA.

You need to write your 8s more clearly -- they look a lot like 0s (or perhaps 6s). In general, make the effort to make you writing, particularly labels and values, very clear.