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Recently I salvaged a piezo humidifier driver board which produces high frequncy AC volage. Naturally I decided to touch it's output. It hurt so I deduced there might be enough voltage to power a nixie tube with it. To my surprise it lit up, but with purple flares around cathodes. So the questions are: what are the drawbacks of powering a nixie tube with high frequency AC, why does it even work and what are these flares?

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    \$\begingroup\$ Corona discharge? It's likely fine to use the driver board as it probably don't produce enough current to hurt anything. The frequency shouldn't really matter unless you go so high that skin effect starts to mess things up \$\endgroup\$
    – crossroad
    Jan 24 at 23:38
  • \$\begingroup\$ The disadvantage is that most circuits designed to drive Nixie tubes only work on DC. \$\endgroup\$
    – Finbarr
    Jan 25 at 0:04
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The issue is current, not frequency. Nixie tubes require a series impedance to limit current to jut a few milliamperes or they will be destroyed. Glow discharge tubes are damaged by sputtering (atoms knocked out of metal by ions), also called "poisoning". Doubling the current cuts useful lifespan by roughly a factor of 10!

Humidifier piezoelectric drivers operate at a few watts power, and without a series resistor (or, for AC, capacitor or inductor), the device won't last very long.

That said, there are other issues with using the humidifier power supply:

  • As others have mentioned, how would you control which elements (digits) are lit? For AC control, you might use an 11-position rotary switch (0-9 and off), but most semiconductor circuits need DC.
  • N.B. The PCB shown does not appear to be isolated from the AC mains, and would pose a severe electric shock hazard.
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  • \$\begingroup\$ Thank you for the detailed answer! I wasnt really going to use this driver In a practical circuit, the question was more of a theorerical kind. Didn't find any info about it on the internet, so decided to ask. The PCBs input is 5v DC, so no worries — the only shock hazard present is low current one and isn't severe 😁 \$\endgroup\$
    – Eduard
    Jan 25 at 14:15

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