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  #11  
Old 11-07-2010, 12:03 PM
notoriusjt2 notoriusjt2 is offline
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recalculating with D=0.316 gives me...

but that answer is incorrect. am I not using the right formula here?
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  #12  
Old 11-07-2010, 12:17 PM
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mik3 mik3 is offline
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What is this formula?

Use this link to find the answer:

http://en.wikipedia.org/wiki/Buck_converter
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  #13  
Old 11-07-2010, 08:21 PM
notoriusjt2 notoriusjt2 is offline
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based on this graph off of wikipedia, it appears that on time is only from 0 to DT.


so would duty cycle actually be DT/T

which would be equal to 0.316?
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  #14  
Old 11-07-2010, 08:39 PM
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The duty cycle is duty cycle, it doesn't change. You set the duty cycle and the output voltage depends on the duty cycle. Now, the relationship of the output voltage to the duty cycle depends whether the converter operates in CCM or DCM.
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Old 11-07-2010, 09:26 PM
t_n_k t_n_k is offline
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Quote:
Originally Posted by notoriusjt2 View Post
recalculating with D=0.316 gives me...

but that answer is incorrect. am I not using the right formula here?
Kindly permit me an observation or two ...

You've been tinkering with these problems for some time now and still seem to be struggling.

As Mik3 & others point out, the particular converter mode of operation and topology dictate the approach required. I'm sure you've grasped that fact.

You asked me some posts back whether I remember the formulas for any given situation. In brief - no I don't. Well that's not exactly correct - I recall the relationship between switching duty and output voltage in a continuous mode buck converter. Rather than remembering a formula which may not be relevant to a particular case, I try to understand what's happening physically and then analyse the circuit.

The present example is a case in point. I came momentarily came 'unstuck' because I didn't initially think it through carefully.

You may derive some benefit from putting the text book aside and systematically analyzing the various cases for yourself - or make sure you understand why a certain formula is relevant for a particular case. Then you may be able to apply the formulas with confidence.
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  #16  
Old 11-07-2010, 10:04 PM
notoriusjt2 notoriusjt2 is offline
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Quote:
Originally Posted by t_n_k View Post
Kindly permit me an observation or two ...

You've been tinkering with these problems for some time now and still seem to be struggling.

As Mik3 & others point out, the particular converter mode of operation and topology dictate the approach required. I'm sure you've grasped that fact.

You asked me some posts back whether I remember the formulas for any given situation. In brief - no I don't. Well that's not exactly correct - I recall the relationship between switching duty and output voltage in a continuous mode buck converter. Rather than remembering a formula which may not be relevant to a particular case, I try to understand what's happening physically and then analyse the circuit.

The present example is a case in point. I came momentarily came 'unstuck' because I didn't initially think it through carefully.

You may derive some benefit from putting the text book aside and systematically analyzing the various cases for yourself - or make sure you understand why a certain formula is relevant for a particular case. Then you may be able to apply the formulas with confidence.
thats a very good idea, i will take that into consideration

however, the graph that i posted from wikipedia and the graph that is in my textbook shows two different on/off concepts. if i would have seen the wikipedia version from the beginning i probably would have gotten this concept much earlier
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