The amount of ringing is usually load-dependent, and is primarily caused by the transformer being non-ideal. Changing the coupling factor from 0.99 to 0.95 should make quite a difference in the ringing. That wont necessarily reflect reality, but it does show you the effect it has. Also, it helps to include the DC resistance of the transformer windings.
I'm not a big fan of snubbers because they cause losses, and you need to be careful about how much current is going thru the capacitor. When I was tweaking the design of the DCDC converter for my NIMO clock, I was getting a thermal hot-spot on the snubber. After some careful adjustment of the duty-cycle and frequency I was able to reduce the ringing and the heat. I implemented current-limiting in the drivers by adding a small resistance between the source and GND; I think it was about 3 ohms. The exact value is determined by the Vgs(on) of the MOSFET, your peak current, and the driving-voltage at the gate. Like the duty-cycle optimization, this was also done on the bench rather than the simulator. On Monday, August 30, 2021 at 6:59:42 AM UTC-7 Paul Andrews wrote: > I created the circuit in LTSpice so I could mess with various components > and see how it affects things like frequency and wave form. Rings like > crazy, so I added an RC snubber, which seemed to also necessitate tying the > primary center tap to ground through a capictor/diode (I don't know if that > is an artifact of the way LTSpice works, or something that is actually > necessary). I copied this from the LT3999 demo board schematic > <https://www.analog.com/media/en/technical-documentation/eval-board-schematic/DC2049A-1-SCH.PDF> > . > > [image: filament_snub.JPG] > I was wondering about voltage sag with this, as there is no regulation and > then re-read your post where Ed Dinning says "Regulation could be a normal > type of regulator set for constant current". No idea what one of those > might be, and whether he is just referring to the 50Hz solution or not. > > On Friday, August 27, 2021 at 8:45:56 AM UTC-4 Dekatron42 wrote: > >> Since transformers isn't my best area, I only have basic understanding of >> the intricacies but I have experimented some with different transformers in >> different cases like when driving Trochotrons and Dekatrons I decided to >> ask an acquaintance who has worked with transformers. His name is Ed >> Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio >> Repair and Restoration forum: https://www.vintage-radio.net/forum/), he >> told me you are welcome to contact him via me so that his email is somewhat >> protected - if you ask him anything related to the VFD-drivers it would >> be kind if you could post something here in this forum so we all can learn >> from it. >> >> This is his answer to my question on what transformer to chose for the >> driver in the article, it sure helped me and I hope it helps anyone who >> wants to experiment with this driver: >> >> "Hi Martin, as it operates about 50/100KHz virtually any ferrite should >> do. It should be a transformer type with no air gap. >> The turns are normally based on the transformer equation for square waves >> >> N= V/ 4 * F * B* Ae >> >> N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for a >> ferrite, Ae the centre pole area in M^2 >> >> The actual losses come out later on in the design process and are not >> part of the initial criteria >> >> Copper sizing is normally based on 3A per mm^2 of cross sectional area >> >> The turns figure he gives looks about right for something like an RM10 >> core, or you could try an EE25 or an ETD29 core in sat F44 materials >> ETD's are the core of choice for this type of application and should be >> readily available. >> >> The more turns that are used the lower the iron losses and the cooler the >> core runs, but the copper losses increase unless fatter copper is used. >> Skin effect will be of minor importance at your frequency >> >> It would also work on a normal laminated core at 50Hz which should not be >> too big as you can run that at up to 1.5T flux density. >> Regulation could be a normal type of regulator set for constant current. >> >> Always many choices in Engineering >> >> Cheers, Ed >> >> Ed Dinning Retired Engineer" >> >> /Martin >> >> On Wednesday, 25 August 2021 at 23:02:48 UTC+2 Paul Andrews wrote: >> >>> When I have time, I will try the driver at the link Martin gave ( >>> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), but >>> without the transformer initially. As far as I can tell, the transformer is >>> just to make the VFD drive isolated so you can pull it up above ground. >>> >> -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/432fc6e0-57ff-4456-b32d-3ac00065601en%40googlegroups.com.
