Voltage clamping for nixie tube driver

Question

I want to design a nixie clock based on a high voltage shift register: the HV5530. I don't what to multiplex the tubes to avoid loss in brightness. My idea is to leave the anodes powered all the time and switch the cathodes by connecting them directly to the outputs of the HV5530. I will use a ribbon cable to connect the tube driver to the board that holds the tubes.

Should I worry about any inductive effects of the wires and the traces on the PCBs? Should I use some voltage clamps or will it work by simply connecting the cathodes directly to the chip?

Answer 1

Unless you use absurdly long wires (as in feet or yards of the stuff) to connect up the circuit, no, inductive effects should not be a problem. You're probably thinking of relays, which need an inductance (the relay coil) in order to work. Nixie tubes aren't appreciably inductive.

All gas discharge tubes, when they are on, are basically constant-voltage devices. And to complicate matters, they need more voltage to turn on (the "strike voltage") than they need to stay on.

So you want to do something to limit the current to the tubes. If you were to just connect them straight to that part then you'd fry the tube, the part, or both. It's likely that the part would die and save the tube, but you couldn't count on it.

Connecting all of the anodes to your +V should work fine, but you want to connect the cathodes to the pull-downs through resistors, whose value is set to get you the rated current through the tubes.