Flyback with LAN transformers
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Posted by Joerg on June 18, 2007, 4:17 pm
Please log in for more thread options Ok, most of us have used LAN tranformers for power transfers. However, their datasheets are skimpy at best and usually contain no information about the core. Of course it won't contain any regular air gap and you cannot easily install one later because it's all potted up. So, did anyone use these for a flyback design yet? Low power, something well under 100mW. -- Regards, Joerg http://www.analogconsultants.com | |||||||||||||||||||||||||||||||
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Posted by Fred Bartoli on June 18, 2007, 5:04 pm
Please log in for more thread options Joerg a écrit : Which voltage from which voltage? Do you really need flyback? I once did a funny self-oscillating one for that kind of power, from 50V supply. Worked pretty well with about 60%, maybe 70, efficiency IIRC. I can dig up the drawing. Anyway how about measuring your xformers? That's so easy... -- Thanks, Fred. | |||||||||||||||||||||||||||||||
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Posted by Joerg on June 18, 2007, 5:25 pm
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Fred Bartoli wrote: > Joerg a écrit :
> >> Ok, most of us have used LAN tranformers for power transfers. However,
>> their datasheets are skimpy at best and usually contain no information >> about the core. Of course it won't contain any regular air gap and you >> cannot easily install one later because it's all potted up. >> >> So, did anyone use these for a flyback design yet? Low power, >> something well under 100mW. >> >
> Which voltage from which voltage? > Do you really need flyback? I once did a funny self-oscillating one for > that kind of power, from 50V supply. Worked pretty well with about 60%, > maybe 70, efficiency IIRC. > I can dig up the drawing. > I've used oscillators as well but then there was no DC component and everything was just fine. It's regular voltage levels, 12V, 24V etc. Flyback is very easy from a topology point of view, and regulates very fast. If there is no other way I'll just do the oscillator thing again. > Anyway how about measuring your xformers? That's so easy...
> Sure. But you know how it goes after that. A couple of years later the manufacturer "improves" the design and ... POOF. -- Regards, Joerg http://www.analogconsultants.com | |||||||||||||||||||||||||||||||
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Posted by Fred Bartoli on June 18, 2007, 5:36 pm
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Joerg a écrit : > Fred Bartoli wrote:
> >> Joerg a écrit :
>> >>> Ok, most of us have used LAN tranformers for power transfers.
>>> However, their datasheets are skimpy at best and usually contain no >>> information about the core. Of course it won't contain any regular >>> air gap and you cannot easily install one later because it's all >>> potted up. >>> >>> So, did anyone use these for a flyback design yet? Low power, >>> something well under 100mW. >>> >>
>> Which voltage from which voltage? >> Do you really need flyback? I once did a funny self-oscillating one >> for that kind of power, from 50V supply. Worked pretty well with about >> 60%, maybe 70, efficiency IIRC. >> I can dig up the drawing. >> >
> I've used oscillators as well but then there was no DC component and > everything was just fine. It's regular voltage levels, 12V, 24V etc. > Flyback is very easy from a topology point of view, and regulates very > fast. If there is no other way I'll just do the oscillator thing again. > > >> Anyway how about measuring your xformers? That's so easy...
>> >
> Sure. But you know how it goes after that. A couple of years later the > manufacturer "improves" the design and ... POOF. > Then take enough safety margins. Given the power level it's probably not difficult. And then what can be improved? Ferrite won't change much and evolves at a very slow pace, and turns/geometry will stay the same or it'd be another part number. -- Thanks, Fred. | |||||||||||||||||||||||||||||||
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Posted by Joerg on June 18, 2007, 6:15 pm
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Fred Bartoli wrote: > Joerg a écrit :
> >> Fred Bartoli wrote:
>> >>> Joerg a écrit :
>>> >>>> Ok, most of us have used LAN tranformers for power transfers. >>>> However, their datasheets are skimpy at best and usually contain no >>>> information about the core. Of course it won't contain any regular >>>> air gap and you cannot easily install one later because it's all >>>> potted up. >>>> >>>> So, did anyone use these for a flyback design yet? Low power, >>>> something well under 100mW. >>>> >>> >>> Which voltage from which voltage? >>> Do you really need flyback? I once did a funny self-oscillating one >>> for that kind of power, from 50V supply. Worked pretty well with >>> about 60%, maybe 70, efficiency IIRC. >>> I can dig up the drawing. >>> >>
>> I've used oscillators as well but then there was no DC component and >> everything was just fine. It's regular voltage levels, 12V, 24V etc. >> Flyback is very easy from a topology point of view, and regulates very >> fast. If there is no other way I'll just do the oscillator thing again. >> >> >>> Anyway how about measuring your xformers? That's so easy...
>>> >>
>> Sure. But you know how it goes after that. A couple of years later the >> manufacturer "improves" the design and ... POOF. >> >
> Then take enough safety margins. Given the power level it's probably not > difficult. > And then what can be improved? > Ferrite won't change much and evolves at a very slow pace, and > turns/geometry will stay the same or it'd be another part number. > Well, I've seen it a few times that a manufacturer switched to another source for the ferrite and problems arose. But you are right, if we had something like 90% margin we'd be ok. -- Regards, Joerg http://www.analogconsultants.com | |||||||||||||||||||||||||||||||
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> their datasheets are skimpy at best and usually contain no information
> about the core. Of course it won't contain any regular air gap and you
> cannot easily install one later because it's all potted up.
>
> So, did anyone use these for a flyback design yet? Low power, something
> well under 100mW.
>