Nixie Power Supplies: have I been doing it all wrong? - Page 1
Forum section: electronics / projects

author: NivagSwerdna
author_rank: Super Contributor
timestamp: November 25, 2019, 07:17:43 pm
content: So the requirement is a 170V PSU of say 10W..To date I have just followed the standard approach of a boost converter from a 9V or 12V supply... It works... But..... and then in the mailbag there was a similar design for 100W... Which got me thinking...Perhaps we are doing this all wrong!This isn't for a Nixie watch so there will be a mains supply available... 240V in old blighty, 120V in the EUso it seems a bit stupid to use a wall wart switching supply to decrease 240V to 12V and then just boost it back up again?Are there any transformer based designs that make more sense? Is is possible to have one that could operate at both continental and UK voltages?Thanks in advance

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 25, 2019, 07:59:04 pm
content: Nah, it's 230/240V in most of the EU. I actually don't know of a country member of the EU that is @120V, but I may have missed it. If it exists, show me that weird beastOTOH, you may have meant the US.Anyway, even though your idea makes sense from an efficiency POV, there's the practicality of it to consider. In many applications these days using Nixie tubes (mostly for the vintage/design look), the PS comes from a separate mains adapter. Unless you really have to, you usually don't want to mess with the mains part yourself for several reasons including safety/CE marking/cost/etc. So all you may have at your disposal is a relatively low DC voltage. You'll have to go the boost converter path.Now if your device includes a mains supply section, you could indeed generate the high voltage for the Nixie tubes directly. Thing is, it'd likely require a custom-made transfomer, which is not cost-effective at all unless you go for high quantities.Additionally, I haven't worked with those tubes before, so I don't know how important that would be that the supply voltage be well regulated or not? If so, there would be little advantage using the above solution IMO, as you would still need a regulating stage.Just a few thoughts.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: November 25, 2019, 08:42:16 pm
content: Quote from: SiliconWizard on November 25, 2019, 07:59:04 pmMy mistake. In fact looking at a list it's only USA, Canada, Japan and a few others that have the lower voltages.Quote from: SiliconWizard on November 25, 2019, 07:59:04 pmSo that's the crux... not worth frying any customer so don't bother?

author: David Hess
author_rank: Super Contributor
timestamp: November 25, 2019, 10:45:58 pm
content: Quote from: NivagSwerdna on November 25, 2019, 07:17:43 pmProduction quantity transformers do not cost any more than standard off-the-shelf transformers so in the past, it was common to just include a separate low current high voltage winding for the Nixie supply. Several of my old salvaged transformers include such a winding.Regulation is not critical because the current limiting resistor ballasts the Nixie element.What I might do for simplicity if my design already has a power transformer is to add another small power transformer and wire it backwards to one of the low voltage AC outputs to produce an isolated 120 volts AC. Alternatively it could be driven with a simple inverter circuit from a low voltage DC supply.

author: james_s
author_rank: Super Contributor
timestamp: November 25, 2019, 10:47:29 pm
content: Nixie tubes are just glorified neon glow lamps, regulation is not critical at all. Most real equipment that used them back in their day used a simple single diode rectifier on a transformer winding. I've used a resistor directly off rectified and filtered mains on a few designs. With others I used a dual primary transformer with one of the primaries used as a secondary in series with one of the other secondaries to get around 180VDC after rectifying and filtering. You can also use two back to back transformers, it's not critical. The advantage of a boost converter is that it's isolated from the mains and you need low voltage to power the electronics anyway. For a commercial product you can also have a UL or whatever certified wall wart and the device itself doesn't need to be compliant.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: November 26, 2019, 11:43:45 am
content: So if you want to not design the mains side due to certification etc.... then you presumeably want to buy an off the shelf power supply with the highest voltage (and sufficient power) to do the job and hence minimize the amount of 'boosting'....So... a 19V Laptop PSU? Is 19V the sweet spot for cheap consumer PSUs?

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 26, 2019, 04:38:08 pm
content: I don't know about the sweet spot... I'd say it would really depend on the quantities you're going to sell. For a >100W PSU, I'd guess laptop PSUs may be indeed one of the cheapest options (provided you want to buy reliable stuff.) For lower power, you have really tons of cheap options on the market.Getting back to your initial concern - again it makes sense in general to want to minimize losses, but another quick thought here is that if you're going to use Nixie tubes in a product, you are already probably not caring much about efficiency or power draw.Oh, and some boost converters have as high as > 90% efficiency at their typical output load, and a decent mains adapter as well, so overall we're talking about >80% efficiency if you select your parts well. Is it that worth it to try and do better, considering the above paragraph?

author: David Hess
author_rank: Super Contributor
timestamp: November 26, 2019, 05:42:07 pm
content: Quote from: NivagSwerdna on November 26, 2019, 11:43:45 amI would not go that far but higher input voltages do make for lower primary side currents which is convenient. Some voltage boosting typologies are better than others at low input voltages so it depends on what you use.12 volts is unusually convenient if you want to support inexpensive lead-acid battery backup.