> First, remember that the B7971 is not a stacked-digit Nixie tube, rather > it's a > planar segmented display. So it's more like an LED character display in > terms of > its circuit topology. > > You don't need an anode resistor if you use cathode resistors. > > The resistor value is Rcath = (Vsupply - Vtube)/Icath >
David, many thanks - this is actually kind of what I figured - very analogous to the LED displays I'm working with, where I wouldn't use an anode resistor either, just cathode ones. I was just a bit thrown by seeing a number of B7971 circuits which use anode resistors, and the spec sheet for it specifying an anode current and a suggested resistor value - is this just overengineering? Thanks also for confirming where the voltage difference is - I should have twigged, again just the same as with an LED version. I guess the voltage and the resistor are interlinked, but using a variable resistor to figure it out sounds like a good plan. The one thing I couldn't figure out was that if I'm sinking the current into a 50V ULN2003A clamped to 47v, would that affect the eg 170v of Vsupply? It sounds like you like to try something new rather than using the old > MPSA transistors. Tell you what, why don't you use an opto triac? For > example the FOD4208, for sure it can support the required LED current. > Michel - thanks also - I didn't even know what a triac was, but now I do :) Definitely an option. I don't have anything against the MPSA transistors, it's just that my understanding of the circuit is lacking - after much research online, I still don't quite get why we don't just use one to switch the tubes, as opposed to the linked PNP and NPN arrangement. (I did, however, figure out that on the same PCB layout, I could use a a TLP627-4 for the lower-current nixie version, and regular individual transistors for the LED one - might go with that even though it's a bit of a hack...) -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msg/neonixie-l/-/zUb2MJfDNGAJ. For more options, visit https://groups.google.com/groups/opt_out.
