Well that makes me feel dumb (which is fine, I will learn)! I should have had the sense to calculate a suitable load value and I should read the data sheets more carefully! Hopefully my trial and error will be instructive to others as well as myself.
I'll do it again with calculated load values, if only to ram the lesson home. I will also get around to trying out the mosfet version of the pmos current source at the start of this discussion. Thanks for all your input into this. > On May 9, 2017, at 12:23 AM, gregebert <[email protected]> wrote: > > A 5K-ohm load with 2mA thru it only drops 10V; with a 200V supply, you would > have 190V across the mosfet. At 2mA load current, that translates to 380mW > dissipation in the mosfet. From the datasheet, the max Theta ja I saw listed > was 170 C/W. That would translate to a 65C rise, which is fine for room-temp > even in a hot climate. > > At 4mA, though, you will get into trouble as you noted. > > Typically you wont see anywhere near that much voltage across a nixie > current-limiter. Assuming 150V typical nixie voltage, and 10V for the > resistor, you will get 40V across the transistor. That translates to 80mW, > and a temp-rise of about 15C, which is plenty of margin. > > A current limiter wont reduce the overall power dissipation, but it will > reduce the variation in nixie current over supply-voltage variations and > nixie aging. > > > > -- > You received this message because you are subscribed to a topic in the Google > Groups "neonixie-l" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/neonixie-l/gbJ0Beiu66I/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To post to this group, send email to [email protected]. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/820f82b0-8b70-4c70-b589-d224f70db2f3%40googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- 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/45D3CF44-2397-4BF4-A7EE-3F03400982D9%40gmail.com. For more options, visit https://groups.google.com/d/optout.
