Electronic Circuit with 2 diodes

[masterchiefo]

Homework Statement

I have to find Vo in every diode state possible.
We know diode Vf = 0.7

Homework Equations

Va-Vc < 0.7 = diode OFF
Va-VC > 0.7 = diode ON

The Attempt at a Solution

State 1:
if D1 OFF and D2 OFF
Vo will be equal to Vi

State 2:
if D1 OFF and D2 ON
Vo will be equal to Vi

State 3:
if D1 ON and D2 OFF
Vo will be equal to 0.7 since the diode is limiting component it at 0.7

State 4:
if D1 ON and D2 ON
Vo= impossible since D2 will not receive enough volt to activate, it will receive less than 0.7 as the resistance will take some.

 

[SammyS]

Homework Statement

View attachment 204809

I have to find Vo in every diode state possible.
We know diode Vf = 0.7

Homework Equations

Va-Vc < 0.7 = diode OFF
Va-VC > 0.7 = diode ON

The Attempt at a Solution

State 1:
if D1 OFF and D2 OFF
Vo will be equal to Vi

State 2:
if D1 OFF and D2 ON
Vo will be equal to Vi

State 3:
if D1 ON and D2 OFF
Vo will be equal to 0.7 since the diode is limiting component it at 0.7

State 4:
if D1 ON and D2 ON
Vo= impossible since D2 will not receive enough volt to activate, it will receive less than 0.7 as the resistance will take some.

What is your question?

To what extent are the diodes to be considered to be ideal ?

 

[mfb]

if D1 OFF and D2 OFF
Vo will be equal to Vi

Only if there is no load (see state 3).

if D1 OFF and D2 ON
Vo will be equal to Vi

Why?

if D1 ON and D2 OFF
Vo will be equal to 0.7 since the diode is limiting component it at 0.7

I don't understand that argument, and the conclusion is wrong. This state is only possible if there is a load at V₀.

if D1 ON and D2 ON
Vo= impossible since D2 will not receive enough volt to activate, it will receive less than 0.7 as the resistance will take some.

I don't understand that argument and the conclusion is wrong.

 

[masterchiefo]

Only if there is no load (see state 3).
Why?I don't understand that argument, and the conclusion is wrong. This state is only possible if there is a load at V₀.I don't understand that argument and the conclusion is wrong.

Each state is independent from each other, its like 4 different problems.
In state 1, both are off so its like there is no diode at all and the second resistor is out as well.
which means Vo = Vi

for state 2, I honestly have no idea how to do it. It confuse me a lot. Can you give me some tips ?

For state 3, I came up with a different solution : Vo = Vi - 0.7

For state 4, I came up with the same solution as state 3, Vi -0.7 = Vo

 

[masterchiefo]

What is your question?

To what extent are the diodes to be considered to be ideal ?

They are perfectly ideal, with vf = 0.7
question is to find Vo in every state as stated in the first post.

Each state is an independent problem.

 

[mfb]

In state 1, both are off so its like there is no diode at all and the second resistor is out as well.

Only if there is no load at V₀. But if there is no load, you never have current through D1!

for state 2, I honestly have no idea how to do it. It confuse me a lot. Can you give me some tips ?

If diode 2 is conducting current, where does the current go? What does that mean for the voltages? There are two things you can say.

For state 3, I came up with a different solution : Vo = Vi - 0.7

Only with a load. Otherwise: Where does the current go?

For state 4, I came up with the same solution as state 3, Vi -0.7 = Vo

Again, that needs a load, and the way you answer state 1 there is no load.
You can make an additional statement in this case, based on the conducting diode 2.Can you have a load attached yes or no?

 

[masterchiefo]

Only if there is no load at V₀. But if there is no load, you never have current through D1!If diode 2 is conducting current, where does the current go? What does that mean for the voltages? There are two things you can say.
Only with a load. Otherwise: Where does the current go?
Again, that needs a load, and the way you answer state 1 there is no load.
You can make an additional statement in this case, based on the conducting diode 2.Can you have a load attached yes or no?

Not really sure how to answer the load attached question, this is all I know about the problem. I believe there is load.
I forgot to mention that it is also possible that some state are impossible.

For state 1, that would mean Vo = R*I

For state 2, I would say current would go to Vo, as D1 can't receive current in that direction. only from Anode to cathode.
so Vo would be -0.7 - R*I = Vo

I want to clear state 1 and 2 before trying again with 3 and 4, one step at a time so I understand the problem correctly

 

[mfb]

Okay, with possible loads then.

For state 1, that would mean Vo = R*I

That is the voltage drop at the resistor, the difference between two potentials - it is not V_i or V₀

For state 2, I would say current would go to Vo, as D1 can't receive current in that direction.

But the resistor can.

so Vo would be -0.7 - R*I = Vo

Right, assuming I is the current flowing through the lower part.

 

[rude man]

.

Staes 1, 3, 4 OK
State 2 wrong.