5V to 250V DC-DC boost converter - Page 1
Forum section: electronics / beginners

author: zlaurin
author_rank: Contributor
timestamp: May 20, 2025, 06:50:21 pm
content: Hello,I wish to create a 5V to 250V DC-DC boost converter to drive a neon/plasma display. This would be my first time making a power circuit / converter but my third PCB project. The 5V would be from a USB-C VBUS and I just need ~5mA total at 250V.I'm not sure where to start. I found TI's WeBench power designer website but it isn't useful since all it can come up with either has a crazy high BOM count or an awful efficiency (~33%). I can't really find anything online either. Everything regarding HV Nixie power supplies is only up to around 220V.I anyone could point me in the right direction I would greatly appreciate it. Thanks in advance.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: May 21, 2025, 02:16:21 am
content: If you're using USB C, consider using a higher input voltage (ex. USB PD of Qualcomm Quick Charge, 9/12/15/20v). Assuming 100% efficiency, you'd need a 5v 2.5a supply, to get the 250*0.05 = 12.5w, which isn't very common, and that 100% efficiency isn't realistic. There's also many old CCFL power supplies from old laptops which used CCFL backlights, which may meet your requirements. Have you looked into those?If you're determined to make this, you'll probably have an easier time creating the 250v using a step-up transformer, instead of an inductor.

author: Psi
author_rank: Super Contributor
timestamp: May 21, 2025, 03:16:30 am
content: You could just get two of these plus a 5V to 5V isolated converter so you can wire the 2nd ones output in series with the first.You would also need to find the feedback resistor and adjust the output voltage down to ~125V so you get 250V in series. (There is some text about the output adjust resistor on the page)https://www.aliexpress.com/item/1005009010121580.html3Asearch%7Cquery_from%3AOne of the pictures says 160V 20mA, so you should have plenty of current.You might even get lucky and only need one, it looks like that thing can be adjusted up to 240V, assuming 240V is close enough to the 250V you need Dunno at what current though.<Add obligatory safety warning about the dangers of high voltage>

author: Buriedcode
author_rank: Super Contributor
timestamp: May 21, 2025, 03:21:25 am
content: The internet is full of "nixie" tube supply designs, often at about 150 - 180V. Many of these designs are questionable (some use the 555...) and often have pretty bad efficiency due to sub-optimal choice of MOSFET, output diode, the use of a 555 instead of any kind of proper switching controller and... being a plain boost converter, rather than a flyback. Sure, they will often work, and are usually quite cheap to make, but not particularly elegant/efficient/regulated. I guess they were designed as somethign cheap, and with generic parts that are easily obtained.A common way to increase the output voltage of boost converters is with a diode/capacitor multiplier - that way you use the boost converter to get up to say 60V or something reasonable, then a few stages of multipliers to get your desired output voltage. Efficiency goes down, but at 5mA output, even at 50% efficient you're looking at 2.5 - 3W in, so about 500-600mA @ 5V.Aliexpress has quite a few small "nixie" supplies thatappearto be rather good quality - tiny SMT flyback transformer, proper switching controller and regulation. I can't speak to their actual quality though as I have never used them, just seem them on the site.A link I paste here many times due to the excellent write up (not mine!) is Flybacks for Dummies:https://www.dos4ever.com/flyback/flyback.htmlIt explains the pros and cons of using a boost converter vs flyback for the nixie tube power supplies nicely.