David_
Advanced Member level 2
Hello.
I have for a while been designing a step-down dc/dc converter, I have no education to speak of nor experience and all I know I have learned online.
That leaves me in many cases unable to use information I find, the following is not 100% serious but there seam to be a safe guard in place allover the application notes related to amongst other things switcher input filter design.
I find papers saying "here we will show you how to design a dc-dc converter input filter" and then goes on to tell me the shocking truth that the filter consists of coils and capacitors! But not a word of how I work out which coils and caps, that's not very useful.
And then I find a few documents that do contain equations and descriptions of those BUT, they always leaves out one or two variables.
So when I try to work it out for my circuit then half way through the final equations there appears variables in the equations that has no explanation of what they are or where they come from and it all falls apart and this happens to me every time. I have not found a single complete solution other than that the second LC output filter if used should be set to 1/10 the switching freq... After input filter I also am searching for output filter design that is more complex than a LC filter, perhaps a two stage LC filter, But I would think that I can solve that my self when I have slayed this input filter monster.
Or that might be incorrect, I've might have found a more or less complete solution for a very basic input filter but it has flaws that can be "easily" cured. And its performans is weak next to a more complex filter.
I have searched for filter design solution for weeks and I have spent so many hours on it that it makes me feel ill, for real. I can't at all count the hours, its a enormous amount of time anyway.
Can someone help me?
I have a mains transformer which outputs 28VAC that's rectified and filtered with a 10,000µF electrolyte. I can not give any info about the regulators input impedance which I know is of vital importance in that the filter output Z must be lower than the regulator input Z at all times and frequency's in order to avoid negative resistance which can leads to oscillations. But I have seen that one can estimate the input Z with some info. I know its about damping and I would really like to be able to use a multi-stage input filter.
The input voltage might be 37V and the output will go between 3V and 33V, that is the thought anyway and I have been made aware that my transformer voltage is somewhat low but lets forget that for know.
The regulator output current is 3A max.
The design uses LT8612.
I know that this might be a big ask but I have run into a wall and I can't think of anything other than to ask here, any guidance what so ever is much appreciated.
With regards
I have for a while been designing a step-down dc/dc converter, I have no education to speak of nor experience and all I know I have learned online.
That leaves me in many cases unable to use information I find, the following is not 100% serious but there seam to be a safe guard in place allover the application notes related to amongst other things switcher input filter design.
I find papers saying "here we will show you how to design a dc-dc converter input filter" and then goes on to tell me the shocking truth that the filter consists of coils and capacitors! But not a word of how I work out which coils and caps, that's not very useful.
And then I find a few documents that do contain equations and descriptions of those BUT, they always leaves out one or two variables.
So when I try to work it out for my circuit then half way through the final equations there appears variables in the equations that has no explanation of what they are or where they come from and it all falls apart and this happens to me every time. I have not found a single complete solution other than that the second LC output filter if used should be set to 1/10 the switching freq... After input filter I also am searching for output filter design that is more complex than a LC filter, perhaps a two stage LC filter, But I would think that I can solve that my self when I have slayed this input filter monster.
Or that might be incorrect, I've might have found a more or less complete solution for a very basic input filter but it has flaws that can be "easily" cured. And its performans is weak next to a more complex filter.
I have searched for filter design solution for weeks and I have spent so many hours on it that it makes me feel ill, for real. I can't at all count the hours, its a enormous amount of time anyway.
Can someone help me?
I have a mains transformer which outputs 28VAC that's rectified and filtered with a 10,000µF electrolyte. I can not give any info about the regulators input impedance which I know is of vital importance in that the filter output Z must be lower than the regulator input Z at all times and frequency's in order to avoid negative resistance which can leads to oscillations. But I have seen that one can estimate the input Z with some info. I know its about damping and I would really like to be able to use a multi-stage input filter.
The input voltage might be 37V and the output will go between 3V and 33V, that is the thought anyway and I have been made aware that my transformer voltage is somewhat low but lets forget that for know.
The regulator output current is 3A max.
The design uses LT8612.
I know that this might be a big ask but I have run into a wall and I can't think of anything other than to ask here, any guidance what so ever is much appreciated.
With regards