Good point... OK, looks like I might be increasing the voltage. Also, my A1A lamps came in the mail, I see now about the voltage holding effect. With a 100k ohm resistor it holds at about 60v, and with a 200k ohm it only drops to about 55. On Jan 20, 7:12 pm, threeneurons <[email protected]> wrote: > >> Thanks... But again, what kind of voltage should I set the supply to? > >> Many seemed to think that 170v was enough, but I guess not... > > I'd go at least 180V, maybe even higher (190V-200V). For a couple of > reasons. > > One, your muxing it. Nixies don't turn-ON instantaneously. There is > some turn-ON delay, which is a function of supply voltage. The higher > the voltage, the quicker the neon ionizes. If you choose 170V or less, > it might be just fine for a direct drive design. On a mux'd design you > may experience some erratic behavior, and come back to us wondering > why the tubes are flickering, even if you picked a total refresh > frequency over 100Hz. Also, if you want to implement PWM dimming to do > some fancy effects like cross fading, you want consistency, which a > quick turn-ON time will give you. Turn-ON times, at 190V, is in the > 20-40uS territory for standard size nixies. There's no period > literature on this. I found out by running a few experiments, and > reporting it back to this group. > > Reason two, the higher the supply voltage, the lesser will be the > variation of anode current, with variation of the tubes inherent > maintaining voltage. The maintaining voltage is usually between 130 to > 150V. > > Say your using a 170V supply, and you design more the middle, 140V. > Pick 2mA. 170V-140V=30V dropped across the anode resistor. 30V/2mA=15K > resistor. If the one tube sets in at 130V, then it will draw > (170V-130V)/15K = 2.7mA. Another tube set in at 150V, and it will draw > (170V-150V)/15K = 1.3mA. That's a two to one variation. > > If you up the supply to 190V, and pick the same (hopeful) target spot > of 140V, and 2mA. The anode resistor is (190V-140V)/2mA= 25K. Pick a > 24K part. Again if a tube comes in at 130V, then the real current is > (190V-130V)/24K = 2.5mA, and the other tube at 150V is (190V-150V)/24K > = 1.7mA. The variation is reduced to ~50%. > > For 200V supply with all else being equal, the results are a 30K > resistor, and anode current variation from 1.7mA to 2.3mA; 35%. > > In all cases, however, you are still in the operating specs of most > standard size (0.5"-0.6") tubes. That's why you can continue with your > design and not wait til your tubes come in. Note big IN-18s should run > at 4mA minimum. > > OT: The 'supply trick' also works with LED displays. And you'll get > much better > consistency going with a 12V supply over a 5V supply. I 1st did this > in the early 80s with a mux'd 8 digit 7-seg display. Not only did I > have to consider the variation of the forward drop of LEDs (equivalent > to nixie's maintaining voltage), but also the variation in saturation > voltage of both the anode and cathode drivers. At 5V, all those 0.2V & > 0.5V (and God forbid, 0.7V) drops add up. At nixie voltages, a half a > volt, or even a volt or two, here and there, are no cause for alarm.
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