Apart from the transformer, I need to find a suitable switching controller. The key to a good power supply is that it produces a stable output. The keyword here is 'regulated'. To produce a regulated voltage, the power supply needs to be able to adjust to the load being placed on it (or, I guess, be so powerful that any load you put on it is negligible). There are quite a lot of tutorials on the internet for building Nixie power supplies, including some that use transformers (none that use an off-the-shelf transformer, hence this little project) and most of them use a switching controller. Here are some:

• Coin cell-powered supply. I built this one. It isn't regulated, but it uses a transformer. I learn't a lot about batteries building this :)
• A regular boost converter. This one has invaluable advice about the actual engineering of building something that works. It uses a regular inductor, not a transformer.
• Obsolete Time Lite, right here on Hackaday. This actually uses a transformer. I was really excited! But I couldn't figure out which transformer, and the project seems to have been abandoned. My big takeaway from this was the specific controller it used.

There are many more, and I'll provide a list from my bookmarks at the end, but my point in listing these is to give a sample that use different controllers. So, I created a spreadsheet of some of the controllers that included a list of specific features. This enabled me to focus on a few that had everything that I wanted. My key requirements were:

• Needed to operate on an input voltage of 3V-12V.
• Needed to be able to produce a high duty cycle, say 90%
• Needed to be able to drive an external MOSFET - rather than having a built-in transistor.
• Needed to have a way of enabling and disabling the output.
• Needed to draw a small amount of current in disabled mode.

I tried the MC34063 first, even though it didn't have a way to disable it - it is widely used and I could get an LTSpice model for it (modelling is a big part of this, as will become apparent).

I tried the LM3478 next, as used in Obsolete Time Lite. This is as far as I got! This made it all the way into my finished supply.

Next up would have been the MAX1771. Everyone swears by it. Many apparently swear at it! It is allegedly very finicky.

After that would have been the LT1619. In many ways this seems like the ideal choice, I just never got this far - the LM3478 seems to work just fine. Plus I didn't want to be swayed by what the excellent Taylor Edge HVPS uses. Part of the reason for this project is to produce my own power supply.

All of these companies sent me samples. Something I am very grateful for.