MarkT:
... Remember power = voltage x current so that at high voltages even a few milliamps can cause overheating....
That is, of course, true, but the idea is to drive the transistors so that they are either "Off" or "Saturated."
If a transistor in a circuit like this is "Off" then it has 200 Volts across it, but the current is less than a microamp.
If the transistor is "Saturated" it may have the full two milliamps (or whatever) of Nixie current through it but the voltage across it will only be about a half of a volt.
Now, I have never actually multiplexed Nixie tubes, so I don't know how effective it might be. I mean the eye tends to be a peak detector, so if you are multiplexing, say, 10 digits, you really don't have to drive each of them with ten times its normal current. I'm not sure how much you do have to drive it.
Nixie tubes that I worked with, years and years (and years) ago typically "looked good" at about 130 volts and 2 mA, but there was considerable variation depending on size, exact color, etc...
Anyhow...
If anyone is interested, I have attached what I think is a practical driver circuit that is "typical" for various high-voltage driver applications. I mean, I gave the title "Nixie Tube Anode Driver," but...
Bottom line: In this circuit the transistors are driven with something like 1/2 mA and 3 mA, respectively, which is enough to ensure saturation when they are conducting.
Do I have to say it? "IWFMYMMV" (It Works For Me; Your Mileage May Vary.)
Regards,
Dave
NixieDriver.pdf (11.4 KB)