As you can see, no shortage of confusing answers and opinions. I thought science long ago abandoned the opinion or Socrates approach: -if one reasons long enough, the truth will reveal itself- long ago in favor of the empirical options. David Forbes is correct that the nixie behaves more like a zener, and cold cathode tubes (what a nixie essentially is) were often used as voltage stabilizers in the old tube era for exactly that property.
I am somewhat at a loss to what you are trying to accomplish. The voltage value you are looking for varies, and at best you may establish a range for your tubes. It may vary from 70 up to as much as 100V. If you are looking for a transistor to use, I'd recommend the MPSA42 for low side switch, and an MPSA92 for the high side if you wish to implement tube blanking. They are cheap, plentiful, and available in through hole as well as SMD. They have never failed me on any nixie tube so far. Check E-Pay for pricing if you are not in a rush. Hope that helps Bill From: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] On Behalf Of alex nolan Sent: Friday, October 23, 2015 9:09 AM To: neonixie-l Subject: Re: [neonixie-l] How much voltage do cathode transistors need to be able to handle? Thanks Bill! Is there any way to calculate that internal voltage drop when for unpowered cathodes (or when all the cathodes are off)? I don't believe I've seen it on any data sheet. On Friday, October 23, 2015 at 8:29:41 AM UTC-4, Bill v wrote: On re-reading your message, if one digit is lit, the voltage drop over the anode resistor can be calculated according to Ohm's law, and determines the "real" voltage present at the tube's anode (Ub - Ura). The remaining open switching transistors now see the calculated anode voltage minus the internal tube voltage drop. This is usually in the order of 70V or so, depending on your tubes and supply voltage. That voltage would jump significantly if all digits were switched off simultaneously, the condition I described in my first reply since there would now be 0V drop over the anode resistor. For that reason tube blanking should not be done by opening all cathode transistors unless they can handle that voltage. Bill From: neoni...@googlegroups.com <javascript:> [mailto:neoni...@googlegroups.com <javascript:> ] On Behalf Of Bill van Dijk Sent: Friday, October 23, 2015 8:14 AM To: neoni...@googlegroups.com <javascript:> Subject: RE: [neonixie-l] How much voltage do cathode transistors need to be able to handle? According to Mr. Ohm, the voltage drop over a resistor is equal to the resistance multiplied by the current. In the off state, the current is 0A, so regardless of the value of the anode resistor, the drop over the anode resistor is 0V. The switching transistor therefore sees the full voltage minus the internal drop in the tube. Bill From: neoni...@googlegroups.com <javascript:> [mailto:n...@googlegroups.com <javascript:> ] On Behalf Of alex nolan Sent: Friday, October 23, 2015 3:30 AM To: neonixie-l Subject: [neonixie-l] How much voltage do cathode transistors need to be able to handle? I'm struggling to get my head around this. But considering the following setup for a nixie tube, wouldn't the voltage across the cathode transistor be close to 0? Most of the voltage should be dropped across the tube itself, with the remained dropped across the current-limiting resistor, right? Does it have to do with the transistors keeping the other cathodes open? If so, how do we calculate those voltages given the tube is on, just to a different cathode? <http://www.mcamafia.de/nixie/images/nix_th01.jpg> -- 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+...@googlegroups.com <javascript:> . To post to this group, send email to neoni...@googlegroups.com <javascript:> . 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