In my opinion, you want a transistor rated at the full anode-voltage in order to ensure reliability. This is probably more critical for MOS devices, because of the risk of oxide breakdown.
Basically, when the cathode driver is off, there is only leakage current, typically less than 1uA. Therefore, the voltage-drop across the anode resistor is about zero. If you consider the nixie to be a resistive device, it's voltage-drop will be about zero. Therefore, almost the entire anode voltage will appear across the driver. For bipolar devices, you might be able to use a Vceo rating less than the anode supply-voltage because breakdown isn't destructive as long as the current is limited. I suspect that NPN drivers with Vceo less than the anode voltage actually begin to breakdown, and as the current increases the voltage-drop across the tube & anode resistor will increase; this causes the voltage across the NPN to drop. At some point, equilibrium is reached. What matters the most is if the leakage current at equilibrium is enough to cause visible glowing. Leakage is exponentially temperature-dependent. I thought about measuring the voltage-drop across an un-ionized nixie with a voltmeter, but my DMM's impedance is only 10Meg so I doubt I would get an accurate reading. -- 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/91cd6917-df25-4dd4-a33b-712d7bb75a4f%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
