# Multiple Diodes Problem

#### SilverKing

Joined Feb 2, 2014
72
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?

#### shteii01

Joined Feb 19, 2010
4,644
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?

#### SLK001

Joined Nov 29, 2011
1,548
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?
It's V1 and V0. V1 is in the upper left corner and V0 about in the center, under the 15k resistor.

#### GopherT

Joined Nov 23, 2012
8,012
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?
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.

#### WBahn

Joined Mar 31, 2012
26,398
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?
It's V1 and V0. V1 is in the upper left corner and V0 about in the center, under the 15k resistor.
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.

#### GopherT

Joined Nov 23, 2012
8,012
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.
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.

#### WBahn

Joined Mar 31, 2012
26,398
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.
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?

#### GopherT

Joined Nov 23, 2012
8,012
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?
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.

#### WBahn

Joined Mar 31, 2012
26,398
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.
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).

#### SilverKing

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

Is it alright?

#### WBahn

Joined Mar 31, 2012
26,398
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.

#### GopherT

Joined Nov 23, 2012
8,012
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).
Whoa, trigger! When did this become about WBahn? Um, insecure much?

#### WBahn

Joined Mar 31, 2012
26,398
Whoa, trigger! When did this become about WBahn? Um, insecure much?
You tried to make it that way. Don't even pretend otherwise.

#### SilverKing

Joined Feb 2, 2014
72
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. ^^"

#### WBahn

Joined Mar 31, 2012
26,398
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.

#### SilverKing

Joined Feb 2, 2014
72
WBahn

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

GopherT

Thanks

#### WBahn

Joined Mar 31, 2012
26,398