That is helpful - thankyou - I shall get some MPSA44 and give it a go! - Richard
On Wednesday, 15 April 2026 at 16:02:52 UTC+1 gregebert wrote: > Your MPSA44 transistor is fine for 3 reasons > 1- You are below BVceo > 2- You are within the safe operating area (SOA) with 4meg of resistance > that limit the max current below 1.5mA at any voltage (in your case, it's > 85uA) > 3- Bipolar devices, unlike MOSFETs, can actually sustain voltages above > BVceo as long as your circuit limits the current. At higher voltages, there > is reverse-junction breakdown resulting in current, but it's not > destructive as long as the current is limited. MOSFETs, however, will have > permanent oxide destruction at any current. > > Those IN-28 boards are cool !! > > > > On Wednesday, April 15, 2026 at 7:48:37 AM UTC-7 Richard Scales wrote: > >> [image: 7SegIN28.jpeg] >> >> On Wednesday, 15 April 2026 at 15:30:51 UTC+1 Richard Scales wrote: >> >>> Hello, >>> >>> I have a number of these '7 segment' panels which are made up of >>> discreet groups of IN-28's. >>> [image: 7SegIN28.jpeg] >>> >>> I am in the UK and am driving them with bridge rectified UK Mains (238V >>> before rectification). >>> >>> Each 'segment' has all it's grids connected to VCC via a 3M, a 1M >>> resistor is also connected so when the end of that is pulled to ground, the >>> grid voltage is reduced to about 85V (assuming 340V peak). >>> >>> If I ground a segment via the 1M resistor, the tubes turn off, if I let >>> it float, the tubes turn on - all good so far. >>> >>> [image: IN28.jpg] >>> >>> My question is this, what safe and reliable mechanism might I employ to >>> make that switch? I was thinking of using MPSA44 NPN transistors which have >>> a Vceo max of 400V, is it as simple as that or is there more to it? >>> >>> Right now I am using a hand made bridge of x 4 UF4007, I would use a >>> proper bridge if this project ever gets anywhere near the finish line! >>> >>> Many precautions are being taken during testing to ensure that the >>> rectified does not go anywhere near me (or anyone else for that matter!). >>> >>> - Richard >>> >> -- 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 view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/dc88f59e-69e2-4327-9665-6289d39afd0cn%40googlegroups.com.
