Is this impossible to solve due to lack of information

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Discussion Overview

The discussion revolves around a homework problem that some participants believe cannot be solved due to a lack of information, specifically regarding the values needed for certain variables. The conversation explores the implications of missing data and attempts to clarify the problem's requirements.

Discussion Character

  • Homework-related
  • Debate/contested
  • Exploratory

Main Points Raised

  • Some participants suggest that the problem cannot be solved due to too many unknowns, particularly in part (ii).
  • Others propose that calculating R2 as a function of Vin is possible for part (i), but express uncertainty about part (ii).
  • Several participants inquire about the source of the problem and whether additional information, such as a Vout value, was provided elsewhere.
  • A participant later identifies that Vout is 7.5V, which allows for some calculations to proceed.
  • There is a discussion about the formula used to calculate Vout, with one participant noting a potential missing parenthesis in the equation.
  • Another participant mentions that the duty cycle is known and relates Vout to Vin, suggesting a possible path forward for part (ii).

Areas of Agreement / Disagreement

Participants generally agree that the problem initially lacked sufficient information, but there is no consensus on how to approach part (ii) or whether it can be fully resolved.

Contextual Notes

The discussion highlights limitations due to missing assumptions and unresolved mathematical steps, particularly regarding the relationship between Vout and Vin.

Enochfoul
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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

 

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I should have said 3b can't be solved
 
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).
 
CWatters said:
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 VIN as a function of R2. :doh:
 
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
 
donpacino said:
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.
 
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?
 
Last edited:
Enochfoul said:
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!
 
What happened to part (ii)? We await with bated breaths ...
 
  • #10
rude man said:
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
 
  • #11
Enochfoul said:
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.
 
  • #12
rude man said:
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.
 
  • #13
Im happy to show the solution for 3bi if you would like
 
  • #14
In post #7:
Enochfoul said:
Using the formula: Vout=Vref*(R1+R2/R2)
There seems to be some parens missing: Vout=Vref*(([/color]R1+R2)[/color][/color]/R2)
Which reduces to the usually seen: Vout=Vref*(1+R1/R2)
 
  • #15
Enochfoul said:
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.
 

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