Thanks everyone for answers, I will probably use some cheap VFD to test the 9.2% PWM @3,3V on high frequency. I'll measure current and will look on it on oscilloscope to see on which frequency the filament will be heated so frequently, that it won't have time to really cool (current will be flat enough on all ON time). I will also test if any kind of soft-start is needed (rushing 3,3V through cold filament sounds risky). as for the aspect of uneven lightning while PWMing - as far as I understand it doesn't change much if I PWM it or not, of course filament-anode voltage will be different, but on such a small tube with 50+ anode voltage I doubt it will make a change. Also, it definitely won't be visible as left-right difference, because in IV-6 filament is a single wire going directly in the middle from top to bottom - so depending on connection I can make top or bottom a bit dimmer.
I've found one project, where author built a H bridge to be able to imitate AC. I think that it might be the way to go, combining H bridging with PWM. Definitely gonna try it some day - I must find a lot of cheap VFDs, here in my country there is someone offering 100x IV-8 for 30 dollars, I'll probably just buy them to have enough "material". https://callumnunesvaz.wordpress.com/portfolio/dogbonevfd/ W dniu wtorek, 7 marca 2017 18:30:16 UTC+1 użytkownik taylorjpt napisał: > > An important aspect of the filament has not been discussed in this > thread: Yes, the filament needs to be heated so that it emits electrons > efficiently but it also sets the potential difference between the cathode > (Itself) and the anodes (the segments). For the later reason you can't > simply calculate the number of watts and then use a PWM to get to that > number. 20% of 5V is technically 1V but that means that one end of the > cathode is at 5V potential (for 25% of the time) and the other end is at > 0V. If the anodes are at 30V then the end of the display nearest the PWM > will get 28V (anode to cathode) and the end nearest the ground side will > get 30V (anode to cathode) or 7% brighter. This is why filaments, > especially for wide multi digit displays, are operated with an AC drive to > minimize the end-to-end voltage differential. For a single digit like the > IV-6 this will result in uneven illumination between the left and right > side of the display. > > Another consideration is the grid to filament bias. The grid for an "Off" > digit is typically held at a negative potential relative to the filament to > repel the emitted electrons thus preventing them from hitting the anodes. > A grid that is not properly biased this way results in segments that are > dimly lit when they should be off because of electrons that sneak through > the grid. This is why the filament is usually biased so that ground is > below the lowest voltage of either end of the filament so that grids at > ground potential are negative with respect to the filament... or else the > grids are operated at a negative voltage for filaments at zero volts. An > IV-6 operated by itself does not need the grid to be used but for a group > of them in a multiplexed display this is critical. If 5 filaments are > connected in series to 5V, they will all get 1V but the cathode to anode > potential (For a 30V anode voltage) for the one nearest the 5V will be > 25.5V (Average) and the one nearest ground will be 0.5V (Average) or a 20% > difference in brightness. > > > > > -- 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 neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/8c816c3c-10b8-4117-963e-a89a1be7bf29%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
