> Last couple of months have been busy at work, but I have been able to spend > some time thinking about this project. > The best source of multi winding inductors I have found so far is the > Versa-Pac series from Cooper Busman. They come with 6 identical windings and > properly connected they will give me a 1:5 autotransformer.
It seems to me that if you wired it as an autotransformer, you'd get a 1:6 unit. Würth Elektronik offers similar configurable units in their "WE-Flex" series, also with 6 identical windings, but they seem a little more expensive. They're available in both forward converter and flyback (gapped) versions. Are you thinking of operating in flyback mode? > Just when I thought that I had found an optimal way of designing RC- and > RCD-snubbers for the switch and the rectifier I got notice of far more modern > alternatives: active clamps. >From context, it sounds like this is a feature built into switching >controllers, and I hadn't heard about it either, so I got curious. I found this data sheet, showing the active clamp circuitry picked out in a different color: http://www.intersil.com/content/dam/Intersil/documents/fn76/fn7654.pdf Looks like all it involves is a couple of capacitors, a FET, and a diode. Should be something you could add to an existing design, although it might be a technique that only applies to forward converters (I need to do more reading, apparently). > When I look at the few exemples of tapped inductor boost converter that > provide any kind of schematic I have not seen any kind of snubber at all, > except for the secondary side rectifier diode. > Is this just a simplification for sake of presentation clarity, or can it > really be omitted? There's a nice discussion of snubbers here: http://softsolder.com/2009/03/06/rc-snubber-resonant-design/ Apparently, they're to prevent ringing, but I'm unsure why ringing would be a problem. It could be because the ringing introduces an AC voltage on top of the supply voltage at the primary, and exceeds the safe voltage for the switching transistor. Again, I'd have to do some more reading. But if that's the case, you may have little to worry about, with a 5 volt supply and a reasonably sturdy switching transistor. > My plan, so far, is to draw snubber networks for the diode and switch just in > case, and just don't put them on the PCB if they prove redundant. Good idea - you could also add the stuff for an active clamp too, I suppose. > With some strategic test points I can measure the leakage inductance of the > autotransformer and this should be a good starting point for an almost > optimal design. > It seems however that the leakage can be measured in different ways. How > would the members of the group proceed with such measurement? The link above suggests this app note for CCFL drivers - as Ed puts it, "Pay no attention to the CCFL stuff, as snubber fundamentals are the same wherever you go." > This became quite some texts, but I guess that my main questions at this > point boild down to: > > Is there any point in considering more advanced topologies such as active > > clamp and active rectification? I'm sure there is such a point (as such techniques exist and are used), but I don't know how to determine that point. It seems to me like an RC snubber is simpler and probably quite adequate to your use, but I'm totally guessing here. > > To which extent are snubber networks necessary? Alas, I'm not much help here, either. - John -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
