> Hello. I'm pretty new to nixies/vfds, and I have some questions on how to > drive a VFD tube before I pick some up on ebay: > > 1) If the filament needs 1.5v at 0.02A, and I'm driving with 5v, would I just > do (5-1.5)/0.02 to get the resistor value? > > 2) For the same filament, if I have a 1.5v source, am I safe to drive it > without the resistor? > > 3) I read that the grid needs a negative voltage to make sure all the > segments are off. Is this true?
Yup, it's true. However, it's easy if you're running your filament from 5V: just put the resistor between filament and ground and hook the filament directly to 5V. Then when you ground the grids/anodes, they'll be more negative than the filament. > 4) Why do some circuits bias the filament at a negative voltage like -30v? So they can drive the anodes and grids by simply grounding them (which makes them 30V more positive than the filament). > 5) Do I need current limiting resistors at the grid and anodes? Nope. > 7) Is it safe to leave grid/anode pins floating? Floating anodes is okay, but you should probably hook unused grids to your most negative voltage (usually ground), so they don't float high and turn on unwanted digits. > 8) If I drive one segment more than the other segments, would it "wear out"? > Kinda like cathode poisoning with nixies? Very slowly. The phosphor used in VFDs is much more durable than the one used in eye tubes, so it lasts a long time. However, a segment that's on most of the time will eventually be dimmer than one that's rarely lit. > 9) What contributes more to tube life? Less filament current, or lower > grid/anode voltages? Is it both? For optimum life, run the filament at its rated voltage, no higher and no lower. Lower brightness (which comes from lower anode voltages) will make the phosphors last longer, however VFDs generally have very long lifetimes. > 10) What is the mechanism in which VFDs fail? If I don't drive them out of > spec, are they "immortal" like LEDs are, or does turning them on consume some > sort of material inside that puts a timer on their lifespan? I'm just curious > that if I leave a VFD clock on, and it's rated for 2000h or something would > it fail in a few months? While they're not immortal, lifetimes from 30,000 to 100,000h are usual. They're very long-lived devices. Generally they get dimmer and dimmer as they get older, but filaments very rarely burn out (and even if one does, most VFDs have multiple filaments and will still function). 2000h is a VERY short lifetime for a VFD. > 11) If I want to dim the VFD, do I pulse the grid or do I pulse the filament? Pulse the grid, you don't want to undervolt the filament (this damages its emissive properties). - John -- 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 post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/9326451F-5705-40D4-AC90-256D11BF434F%40mac.com. For more options, visit https://groups.google.com/d/optout.
