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ripple factor in fly back converter

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veladimir

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hello
I'm going to make a offline fly back converter and i have heard that its recommended to set ripple factor to 0.1 to 1.
but all of core i found have big Al (small reloctance) and after wiring they have large inductance even with reasonable air gap. then i have to use very low ripple factor.
I want to know what restrictions is for ripple factor and what will happen when using low ripple factor for example Krf=0.02

thanks
 

It's usually not a demanded ripple current number that restricts the design and e.g. sets the AL value. It's the other way around: Maximum core flux due to saturation limits or loss considerations requires a maximum AL value and sets a particular current ripple. This means, unless you use an uneconomic large core, you'll hardly achieve 0.02 ripple factor.
 
FvM said:
It's usually not a demanded ripple current number that restricts the design and e.g. sets the AL value. It's the other way around: Maximum core flux due to saturation limits or loss considerations requires a maximum AL value and sets a particular current ripple. This means, unless you use an uneconomic large core, you'll hardly achieve 0.02 ripple factor.
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I choose core according to tables suggested with fairchild datasheets and i set the primary wiring number based on saturation restriction then i have large inductance , where i made mistake that it is not uneconomic ?

best regards
 

Sounds unlikely. Either the core is larger than necessary, or there's a calculation fault in some step.
 
FvM said:
Sounds unlikely. Either the core is larger than necessary, or there's a calculation fault in some step.
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thank you my friend . you are right ! I have been make a mistake.
but another question !
i read AN4137 fairchild application note but I dont understand design feed back loop section that present one-zero one-pole compensation circuit . what is the necessity of one-zero one-pole compensation circuit ? would you like to
explain more about this issue?
 

hi
no one has information ?
help me please?
 

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