I'm afraid all active current limiters will change with temperature, just some will be affected more and some less. But small changes (0,1mA or less) won't be critical in a nixie clock, I think. So if a circuit will be stable enough to provide desired current +-0,1mA in temperature range of 0°C to about 70°C, with supply voltage changing 20V max - I'd call it good enough. About variations of Vgs curves - within one production batch of transistors differences are usually minimal. So after ordering a batch of transistors you have to check just one of them and you can safely assume that all other will behave almost identically. Vbe differences in current mirrors are much more critical, as the difference gets amplified.
If those two factors are still too big, then you have to use a circuit using a current sensing resistor, an amplifier of Rsense voltage drop and a drive transistor. Multiply that by 15 segments and by number of tubes and you end up with a large and costly circuit. I think that that level of current stability is not needed here. I'll test J-FET current limitter with a hot air gun - how it behaves in temperature range of 20-150°C, both with 5V and 30V dropping on it. If I find some time, I'll do the same with a very similar circuit using LM317 (similar - both use only one resistor and one cheap active component). W dniu sobota, 8 kwietnia 2017 05:02:25 UTC+2 użytkownik gregebert napisał: > > My concern with current limiters that rely heavily upon the datasheet > specs (Vgs for Depletion-mode regulator; Vbe for current-mirror) is that > variations due to process & temperature will have significant impact on the > actual current. Using a slightly more complex+costly design will mitigate > this; well-worth it in my opinion when you consider the value of the tubes > you are protecting. > > > -- 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/d4ac524b-2a5b-4293-99a0-4a731ebd84bd%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
