Is this impossible to solve due to lack of information

[Enochfoul]

Homework Statement

I came across this question in another forum and the members of the group said it can't be solved due to lack of information. Can anyone solve it?

Homework Equations

The Attempt at a Solution

 

[Enochfoul]

I should have said 3b can't be solved

 

[CWatters]

That question has been posted on this forum recently. I don't think it can be solved. Too many unknowns. I think the best you can do is calculate R2 as a function of Vin for 3b(i) but then you are stuck for (ii).

 

[Tom.G]

I think the best you can do is calculate R2 as a function of Vin for 3b(i) but then you are stuck for (ii).

And for (ii) solve for V_IN as a function of R2.

 

[donpacino]

Where did this problem come from?
any chance a Vout value is given on a previous page?

If you had Vout you could get both as a function of Vout

 

[Enochfoul]

Where did this problem come from?
any chance a Vout value is given on a previous page?

If you had Vout you could get both as a function of Vout

Its an assignment question which I believe they have messed up on by omitting information.

 

[Enochfoul]

Hi

The missing piece has been found Vout= 7.5V

Using the formula: Vout=Vref*(R1+R2/R2)

Vout=1.25(10+2/2) = 7.5

R2 must be 2 does that look right?

 

[donpacino]

Hi

The missing piece has been found Vout= 7.5V

Using the formula: Vout=Vref*(R1+R2/R2)

Vout=1.25(10+2/2) = 7.5

R2 must be 2 does that look right?

looks good to me!

 

[rude man]

What happened to part (ii)? We await with bated breaths ...

 

[Enochfoul]

What happened to part (ii)? We await with bated breaths ...

The problem stated had missing info. The Vout should have been 7.5V. Sorted it now thanks the lecturer missed it off by accident

 

[rude man]

The problem stated had missing info. The Vout should have been 7.5V. Sorted it now thanks the lecturer missed it off by accident

Yes I know, and part (a) was I presume solved. But what about part (b)? It's still an interesting problem.

 

[Enochfoul]

Yes I know, and part (a) was I presume solved. But what about part (b)? It's still an interesting problem.

D=Vout/Vin. There are 2 knowns in the question Duty Cycle which is 30% and Vout which is 7.5V. So Vout is 30% of Vin.

 

[Enochfoul]

Im happy to show the solution for 3bi if you would like

 

[Tom.G]

In post #7:

Using the formula: Vout=Vref*(R1+R2/R2)

There seems to be some parens missing: Vout=Vref*((R1+R2)/R2)
Which reduces to the usually seen: Vout=Vref*(1+R1/R2)

 

[rude man]

D=Vout/Vin. There are 2 knowns in the question Duty Cycle which is 30% and Vout which is 7.5V. So Vout is 30% of Vin.

The answer is correct. Good going.