One of the challenges of working with a project like this that uses “exotic displays” such as Vacuum Fluorescent or Nixie Tubes is that these displays are very fickle with the way they are driven. VFDs typically need about 20-80 volts to light up the anode/grid segments of the display, and because they are vacuum tubes, they also need a filament to be heated up with about 1-5 volts.

There are a variety of ways to get the higher voltages. If the tubes you are using are not too picky you might get away with 12-24 volts, but if you want to support a variety of displays, and if you want to be able to drive the displays with multiplexing (i.e. flashing the segments+digits one at a time, in rapid succession), then you will need up yo 80v.

I have very little knowledge of analog circuitry and switch-mode power supplies, so I wanted to change that, and researched various ways to get the voltages I would need, and settled on a switch-mode PSU based on the MAX1771 step-up converter. After some trial and error with procuring the right components, I settled on a design based on this switch-mode power supply. This circuit was designed for nixies, which need up to 250 volts. It’s overkill for my current requirements but I want to support a variety of displays, and may use nixies at some point.

It took me a long time to get this working and I smoked a few mosfets and 1771s along the way, so it was pure joy when I saw the voltmeter jump up to 50v. After playing with some resistor values I soon had it cranking out 250v from a 5v supply. I added a trimpot to make it adjustable from about 25-100v.

I then got out one of the russian IV-18 tubes from my collection and hooked it into a breadboard, and ran 5v into a trimpot and then to the filament, and ran the HV power to the anodes/grid. After some trial and error I finally got it to light up. It seems to like about 60v.

The IV-18 tubes more than are worthy of a close-up. I am quite enamoured with them.