I just want to add that for the low current scenario, the voltage should be consumed by the nixie. The voltage across the LM317 will continue to drop with reducing current, down to about 0.75V at 0.2mA under a test I did. Only in overcurrent would there be an issue, as the voltage across it will increase beyond it's limit.
On Monday, 27 March 2017 02:36:01 UTC-4, Tomasz Kowalczyk wrote: > > It all depends on R11 and desired current. Most nixies have a minimum > voltage drop of around 120V (although they will maintain 130 for most of > the time, they will just continue to work with lower voltage), so if > voltage drop on R11 is more than (supply voltage - 120V - > LM317_max_voltage), then it is safe - the only case where the nixie doesn't > have that voltage drop is when it is internally shorted. > In this schematic, assuming that U15 is fully open, so voltage at R11 left > side is just about 180V, everything will be okay - the LM317 is set for > 8mA, so voltage drop over R11 would be around 34V and everythin would be > safe. The problem is that if current is significantly lower that (nixie is > heavily poisoned), then stuff can get bad: as far as I understand, R11 > voltage drop has to be lower (Ohms law), so the voltage across LM317 will > get higher, I think - it has to drop somewhere. > Long story short, you are right - LM317 can fail in non-standard > situation. That's why I would go for a two-transistor design using MMBTA42 > (or MPSA42), which will withstand almost anything. The only problem is > power dissipation - 5mA with 50 volts drop across current limiting circuit > is 0,25W. With such constant current design one should lower HV voltage to > minimum (just above striking point of all nixies), normally the > significantly higher voltage (200V) is used to make choosing limiting > resistor easier. > > W dniu poniedziałek, 27 marca 2017 04:17:46 UTC+2 użytkownik gregebert > napisał: >> >> I dont see anything fundamentally wrong; I just have paranoia about >> running devices in an environment where this is potential for overvoltage. >> The LM317 is rated for ~35V, and the HV supply is around 180V, so you are >> relying on the voltage drop across the nixie tube. There are all kinds of >> unexpected things that happen during power-up/down; maybe there are >> scenarios that could damage the LM317. >> >> >> >> >> -- 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/0d854699-9439-4c03-ad10-376766ebada2%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
