Tiny neon bulb driver circuit - Page 1
Forum section: electronics / projects

author: prosper
author_rank: Regular Contributor
timestamp: February 11, 2025, 08:50:42 pm
content: I'm trying to build the smallest possible circuit to light a neon bulb. Ideally, I could fabricate some round PCBs about 6mm (or less) in diameter, and incorporate them into a bulb holder or bezel of some sort. The end goal is to be able to use neon NE-2 bulbs in a circuit the same way as you would use a LED, for a retro aesthetic. The main difficulty is that I want to light them with AC so that both electrodes glow; which eliminates a DCDC boost circuit. Power Efficiency isn't a primary concern, but I'd like it to keep the input current requirement to about 20mA or so. The NE-2 needs about 100V to strike, and maybe 1/2mA at 80V continuous. Right now, I'm working with the circuit attached below.I have two questions:1. What are my options for a transformer that's both tiny and has a high ratio of turns? Right now I've hand wound on an EE5 core which really sucks as it needs a LOT of windings, and it isn't as small as I'd like.2. Are there any circuit improvements you can think of or alternate circuits to consider?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 11, 2025, 10:10:44 pm
content: Getting that step-up from a LVC gate might be a big ask?I did see these go past in recent news, in SOT26https://www.nexperia.com/products/analog-logic-ics/isolation/transformer-driversThose would allow a less-ideal transformer.

author: prosper
author_rank: Regular Contributor
timestamp: February 11, 2025, 10:44:28 pm
content: oooo! that's a cute part!Yeah, the LVC seems to mostly work, but I need to do some more testing and simulations to see if it'll be reliable enough; it's definitely not designed for this purpose.

author: David Hess
author_rank: Super Contributor
timestamp: February 12, 2025, 12:06:20 am
content: The output from a flyback converter may be AC coupled through a capacitor to drive a neon bulb. This would allow the use of existing flyback transformers and integrated flyback switching regulators.

author: prosper
author_rank: Regular Contributor
timestamp: February 12, 2025, 01:39:25 am
content: you know, I tried that but I gave up on it pretty quickly... it probably bears going back to it and playing around some more. Added advantage is that I could achieve high boost ratios without as many turns. If I size the capacitor carefully, I bet I could run in open loop, too, reducing the size a bit

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 12, 2025, 05:06:19 am
content: Quote from: prosper on February 11, 2025, 10:44:28 pmAnother part could be the Nexperia 74LVC1G19, which gives two push-pull outputs for twice the swing ?lcsc have MX6505T - similar to the Nexperia part above, tho with higher FET rating, so can power the coil from 12V for less of a leap.(still needs 5V for the core)

author: Zero999
author_rank: Super Contributor
timestamp: February 12, 2025, 09:40:21 am
content: How about the SN6501?https://www.ti.com/lit/ds/symlink/sn6501.pdf

author: RoGeorge
author_rank: Super Contributor
timestamp: February 12, 2025, 11:58:43 am
content: I would use a 555 + a current transformer, or for more dramatic effect a miniature Tesla-coil.

author: prosper
author_rank: Regular Contributor
timestamp: February 12, 2025, 02:52:35 pm
content: you know, I'd wondered if a current transformer might work. I'll probably give it a shot. They're available in really small packages with high ratios. What's stopped me so far is the really tiny primary inductance, and liklihood of saturation problems. They're not characterized for this sort of operation, so the datasheets are of limited use.

author: TurboTom
author_rank: Super Contributor
timestamp: February 12, 2025, 10:19:31 pm
content: As the transformer, you may experiment with trigger coils for Xenon flash tubes.Here are some examples shown.They are meant to be powered by a capacitor charged to a few hundred volts and then generate several kilovolts at their secondary, but driven with a high frequency low voltage signal, they will be very well suited to power your Neon indicator.

author: prosper
author_rank: Regular Contributor
timestamp: February 12, 2025, 10:44:08 pm
content: Interesting idea. I've also experimented by winding a new primary onto a drum inductor. Works OK in flyback or flyboost mode. Not so great as a resonant converter.Also, the attached works; a classic 'joule thief' type oscillator. Various transformers work with it; the smallest one I've found was to wind a few dozen turns around the body of one of those 'resistor-style' axial inductors. (specifically, 50 turns with a tap at 25t over a 10mH '1W' inductor) Surprisingly, efficiency is actually quite decent; lighting a neon bulb at about 30mA/1.25V. Stability is poor though, and it's very picky about supply voltage.

author: amyk
author_rank: Super Contributor
timestamp: February 13, 2025, 01:40:46 am
content: What input voltage are you looking for?

author: Analog Kid
author_rank: Super Contributor
timestamp: February 13, 2025, 02:28:55 am
content: Quote from: prosper on February 12, 2025, 10:44:08 pmWait, what? 1.25V?No neon bulb is going to light at that voltage. Is that a typo?I've built lots of joule thieves that run on 1.5 volt cells and will brightly light a high-brightness LED, but certainly not a neon bulb.

author: squadchannel
author_rank: Frequent Contributor
timestamp: February 13, 2025, 03:26:17 am
content: If it were 1.25V, it would just be a light bulb.Neon requires about 150V.

author: prosper
author_rank: Regular Contributor
timestamp: February 13, 2025, 04:04:29 am
content: the joule thief posted above takes in 30mA from a 1.25v source, and boosts it to the point a neon bulb lights up.

author: Analog Kid
author_rank: Super Contributor
timestamp: February 13, 2025, 04:05:16 am
content: Now that's believable.

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2025, 08:28:41 am
content: Quote from: prosper on February 12, 2025, 10:44:08 pmDoes it light both electrodes?I was going to suggest a Joule thief circuit, but decided against it because the output waveform isn't symmetrical, therefore I would expect it to light one electrode more than the other.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 13, 2025, 09:03:29 am
content: You could probably do it without a double-wound transformer - should be possible with a simple flyback output stage - transistor (e.g. MPSA42) with inductor ( low millihenries) to positive with the neon across it, driven by a squarewave.

author: prosper
author_rank: Regular Contributor
timestamp: February 13, 2025, 03:01:25 pm
content: Quote from: Zero999 on February 13, 2025, 08:28:41 amIt does, but not very well/evenly, as you noted. Capacitively coupling the output also makes the circuit that much more finicky, too

author: Wolfram
author_rank: Frequent Contributor
timestamp: February 13, 2025, 06:36:09 pm
content: The ATB322515/322524 come to mind, as compact step-up transformers with a useful ratio. They are made for flyback operation so primary inductance is pretty low, and wiring them for self-oscillation might be tricky on account of them only having a single primary, but it's something to look into. Flyback only provides unipolar pulses, but a capacitor in series with the neon lamp, as shown in prosper's diagram, solves this.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 13, 2025, 07:49:19 pm
content: There are some chips designed to drive EL lamps that may be of interest, e.g. MIC4826 - these are typically flyback boost followed by an H-bridge - could be good if you care about lighting both electrodes.It is is also not too hard to use a similar architecture with discrete parts, though finding small, high-value inductors may be tricky

author: prosper
author_rank: Regular Contributor
timestamp: February 13, 2025, 07:57:49 pm
content: Quote from: mikeselectricstuff on February 13, 2025, 07:49:19 pm100%. Building a circuit that will light a neon bulb is trivial. But finding a tiny inductor is trickier. I have some parts on order to try... I think I'm gonna revisit a flyback topology with an ac coupling cap again, driven by a simple pulse generator without feedback

author: Langdon
author_rank: Frequent Contributor
timestamp: February 13, 2025, 08:02:17 pm
content: There are neon bulbs that can be powered by 120VAC, directly from the mains (perhaps through a resistor of some sort).Why do you need a transformer?

author: Analog Kid
author_rank: Super Contributor
timestamp: February 13, 2025, 08:24:41 pm
content: Quote from: prosper on February 13, 2025, 07:57:49 pmHow about winding your own? I've done that for low-voltage applications (Joule thieves) and it has always worked well. I just use small pieces of ferrite rod and magnet wire.

author: prosper
author_rank: Regular Contributor
timestamp: February 13, 2025, 08:50:16 pm
content: Doable, but it's a pain to put a hundred plus turns onto a 4mm core

author: themadhippy
author_rank: Super Contributor
timestamp: February 13, 2025, 09:15:19 pm
content: QuoteA cordless drill makes it more bearable

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2025, 09:28:06 pm
content: Quote from: Langdon on February 13, 2025, 08:02:17 pmTwo possible reasons:1) A battery powered device.2) Controlling the neon from a microcontroller and it's easier to switch 5V, than mains.

author: Xena E
author_rank: Frequent Contributor
timestamp: February 13, 2025, 11:47:04 pm
content: Size you're looking for will be a hard ask for a 200mW inverter.I've used miniature CCFL inverters for neon driving: find on the auction sites for very little coin.If you want to roll your own there's loads of inspiration from prior art, just search CCFL circuit... but the inductor as always will be the chore, personal advice, unless you want the challenge I'd buy a solution...X

author: RoGeorge
author_rank: Super Contributor
timestamp: February 14, 2025, 12:07:09 am
content: Is this for production, or for a one-off art installation?How many of these Neon-LEDs do you need?

author: Langdon
author_rank: Frequent Contributor
timestamp: February 14, 2025, 12:10:23 am
content: Quote from: Zero999 on February 13, 2025, 09:28:06 pm120V can easily be switched with a relay or SSR; the amperage is not great.If it's battery powered, why would you use neon?LEDs are usually the way to go for battery power.

author: Analog Kid
author_rank: Super Contributor
timestamp: February 14, 2025, 12:13:23 am
content: Quote from: Langdon on February 14, 2025, 12:10:23 amGo back and read the original post:QuoteSame reason some of us like to use nixie tubes instead of LED/LCD displays.

author: themadhippy
author_rank: Super Contributor
timestamp: February 14, 2025, 12:20:02 am
content: good luck getting a ssr to turn off just a neon

author: prosper
author_rank: Regular Contributor
timestamp: February 14, 2025, 12:29:33 am
content: Quote from: RoGeorge on February 14, 2025, 12:07:09 amOnce i come up with something I like, I envision making up a bunch of small round PCBs, then 3d printing some lamp holders that contain the pcb and bulb. A bulb, a base, and two leads that i could run off an MCU, or whatever.Just for personal use, but I do have about a thousand old ne2 bulbs, so, more than I'd want to hand-wind.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 14, 2025, 12:43:19 am
content: 1kpcs. hand-made of whatever item (doesn't matter what item) will be painful to manufacture by yourself, no matter the technical solution. No matter what you would hand-made, when it's above 100pcs., hard work and determination is not enough. It will need serious thinking about manufacturing processes.Maybe search on Alibaba a small assembly house that can manufacture it for you. They can do a custom coils/transformers, too, if needed, or maybe repurpose existing coils/transformers from LED light-bulbs.

author: eliocor
author_rank: Unknown
timestamp: February 14, 2025, 01:19:52 am
content: TDK ATB3225mini transformers series, perhaps ?Edit: sorry: Wolfram already suggested them...

author: TurboTom
author_rank: Super Contributor
timestamp: February 14, 2025, 01:28:56 am
content: I would try the following: Use one of the flash lamp trigger coils as I suggestedhereand drive it with a tiny class D audio amplifier chip like aPAM8302A. Short the inputs together, properly bypass the power supply and maybe install a small cap in series with the primary of the coil in order to limit power -- you may as well use a resistor in series with the output. Three / four tiny components and you're good to go.

author: prosper
author_rank: Regular Contributor
timestamp: February 14, 2025, 01:47:40 am
content: i have a handful of various coils and chips suggested on order. I do have a bunch of similar audio amps in my stash, so I'll definitely give them a try

author: prosper
author_rank: Regular Contributor
timestamp: February 14, 2025, 01:51:44 am
content: sorry, i didnt mean to suggest that I'd be making 1000. More like thats the absolute upper limit of what I'd consider. And definitely not all in one go, either. I have a project in mind that would need about 60 in total, so thats a more realistic first batch size.Now that I think about it, I might also 3d print some 8x8 matrices too, and do up some sort of blinkie with them.... but for something like that, I'd build up a single larger power supply, not a few dozen small onesQuote from: RoGeorge on February 14, 2025, 12:43:19 am

author: TurboTom
author_rank: Super Contributor
timestamp: February 14, 2025, 03:09:13 am
content: Quote from: prosper on February 14, 2025, 01:47:40 amJust be sure they are class D since the PWM frequency is used to drive the coil and not the (non-existant) modulated AF. Also, the frequency should be somewhere in the 150...300kHz range, of course also somewhat depending on the coil's primary inductance.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 14, 2025, 03:11:48 am
content: Quote from: prosper on February 12, 2025, 10:44:08 pmYou can add a RC element to the base drive, so the base-emitter junction DC restoration gives a sort-of AGC action, to make it 'less picky'.Next step would be current or voltage regulation.Addit: eg current regulation diodes like WS7628(27.5-28.5MA) WS7612(11.5-12.5MA) WS7614(13.5MA-14.5MA) have useful 0.7-14V operating regulation regions.What voltage do you want to run this from?Quote from: prosper on February 13, 2025, 03:01:25 pmMaybe adding a resonant cap can make the secondary waveform more symmetric, and improve that electrode effect?Of course, all of this edges up the BOM & size.

author: Analog Kid
author_rank: Super Contributor
timestamp: February 14, 2025, 03:16:36 am
content: If you have any interest in winding your own transformer you could check outthis postI made which includes that in a project. May or may not be helpful.

author: squadchannel
author_rank: Frequent Contributor
timestamp: February 14, 2025, 03:32:35 am
content: https://www.analog.com/en/resources/technical-articles/small-highvoltage-boost-converters-guide.html6mmx8.5mm

author: prosper
author_rank: Regular Contributor
timestamp: February 14, 2025, 03:58:10 am
content: Quote from: PCB.Wiz on February 14, 2025, 03:11:48 amideally, from 3-5V.

author: prosper
author_rank: Regular Contributor
timestamp: February 14, 2025, 04:01:01 am
content: Quote from: squadchannel on February 14, 2025, 03:32:35 amI've seen that AN before, had forgotten about it. Might be a good candidate for a capatitor decoupled experiment

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2025, 08:05:24 am
content: Quote from: Langdon on February 14, 2025, 12:10:23 amAn SSR won't switch a neon. A mechanical relay is bigger and uses more power than a tiny voltage boost circuit.

author: Langdon
author_rank: Frequent Contributor
timestamp: February 15, 2025, 02:36:32 am
content: Quote from: Zero999 on February 14, 2025, 08:05:24 amWhy can't an SSR switch it?

author: themadhippy
author_rank: Super Contributor
timestamp: February 15, 2025, 02:50:29 am
content: ssr's dont fully turn off,they leak a few milli amps,and as a neon will light up on mouse farts theres enough leakage current to keep them glowing

author: Analog Kid
author_rank: Super Contributor
timestamp: February 15, 2025, 03:08:38 am
content: I just confirmed that experimentally. Connected to a SSR, the neon bulb will glow even without any applied control voltage.That's 10 minutes of my life I'll never get back ...

author: Langdon
author_rank: Frequent Contributor
timestamp: February 15, 2025, 06:49:28 pm
content: Quote from: Analog Kid on February 14, 2025, 12:13:23 amWhy not just use Red LEDs and make themlooklike Neon?Who could tell their actually fake?

author: Analog Kid
author_rank: Super Contributor
timestamp: February 15, 2025, 07:30:21 pm
content: Quote from: Langdon on February 15, 2025, 06:49:28 pmYou really don't understand the aesthetic here.Why would anyone want to use nixie tubes when there are much easier to use low-voltage numeric displays available?You're young, so you can be forgiven.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 15, 2025, 11:27:50 pm
content: Quote from: prosper on February 11, 2025, 08:50:42 pmThe suggestion to use a colour matched LED is not totally silly.Google finds LED tech has advanced with more phosphor-tuned colours available(mentioned herehttps://www.eevblog.com/forum/projects/replacing-neon-lamp-with-led/)https://www.optosupply.com/newproduct/detail.asp?id=1898https://www.optosupply.com/product/list.asp?id=89and it seems there are stocks, of this orange peach, for a slight premium over vanilla LEDs.https://octopart.com/search?q=OSCG4L5111A&currency=USD&specs=0OSCG4L5111A 59stk 0.600/100

author: themadhippy
author_rank: Super Contributor
timestamp: February 16, 2025, 12:40:01 am
content: Quotebut then you need 2 leds and extra circuitry to give it that shimmery flickery look of neon

author: Langdon
author_rank: Frequent Contributor
timestamp: February 16, 2025, 12:47:47 am
content: Quote from: PCB.Wiz on February 15, 2025, 11:27:50 pmWhat about a UV LED that lights up a phosphor which emits identical wavelengths to a neon bulb?That way, you could get multiple hues.(In general, most LEDs only emit one hue)

author: Langdon
author_rank: Frequent Contributor
timestamp: February 16, 2025, 12:51:35 am
content: Quote from: themadhippy on February 16, 2025, 12:40:01 amThe Neon itself is not flickery, the power is.Power is 60Hz, so any gas discharge lamp will flicker at 60Hz.

author: themadhippy
author_rank: Super Contributor
timestamp: February 16, 2025, 01:00:32 am
content: Quoteif they flickered at 60Hz here i'd be very worried

author: eliocor
author_rank: Unknown
timestamp: February 16, 2025, 02:15:51 am
content: Ehm....I think the flicker is 100 or 120 Hz

author: Analog Kid
author_rank: Super Contributor
timestamp: February 16, 2025, 02:37:55 am
content: Quote from: eliocor on February 16, 2025, 02:15:51 amRighto. And alternating from electrode to electrode.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 16, 2025, 05:34:17 am
content: Quote from: themadhippy on February 16, 2025, 12:40:01 amYes, if that was very important to you, two LEDs could conduct on different polarities, to mimic the alternate illumination of a neon.Optosupply have a 3528 package that could side by side mount OSCG4LS1C1A 14.5c/100+

author: Langdon
author_rank: Frequent Contributor
timestamp: February 16, 2025, 07:02:07 pm
content: Higher frequency = smaller transformer.What about a 555 running in astable mode at a high frequency with a small little transformer?Use a 1.5pF ceramic cap, a 10kΩ resistor, a 1MΩ resistor, and a 555 to drive a transformer.Use 2 fast diodes to protect the 555 from tranformer inductance.Usually, it is recommended to bypass pin 5 to GND with a 0.01µF cap (ceramic disk caps are cheap and recommended).(make sure the voltage on the 555's output pin is never well above VCC or well below GND)If the capacitor makes annoying noise, use neutral-cure silicone or something to shut it up.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 16, 2025, 10:10:37 pm
content: Quote from: Langdon on February 16, 2025, 07:02:07 pmPerhaps, but the 555 itself borders on large.There are SOT23 sized alternatives already mentioned that are designed to drive transformers, and you can also get gate drivers and small motor drivers in SOT23-6 packages.

author: Xena E
author_rank: Frequent Contributor
timestamp: February 16, 2025, 11:54:12 pm
content: I'm not really getting what the TS application is for this, but, if they require to switch on individual neons from low level signals I'd suggest a single low frequency AC supply, (for the ambience of the vintage neon), and isolate and interface with the low voltage control circuitry using an opto triac such as the MOC3020. (As an example, other newer parts available)https://www.amazon.co.uk/10PCS-MOC3020-DIP6-Optocouplers-Optocoupl/dp/B09PYL9DKMAt around the 25c per single they're not breaking the bank, and their current capacity will be easily adequate to drive a neon with no problems. Holding current can be increased by putting a capacitor across the load if necessary.X

author: prosper
author_rank: Regular Contributor
timestamp: February 17, 2025, 12:01:18 am
content: Quote from: Langdon on February 16, 2025, 07:02:07 pmIm sort of not a 555 fan. Too big for what it does, takes too many passives to set up, doesn't go rail to rail, kinda slow, and power inefficient.You can get TWO rail to rail astables out of a sot23 lmv14 with a single resistor and cap for each

author: Zero999
author_rank: Super Contributor
timestamp: February 17, 2025, 06:51:51 pm
content: Quote from: Langdon on February 16, 2025, 07:02:07 pm1.5pF where? That's far too smaller capacitor for use with a 555. Such a small capacitor also needs careful attention to be paid to the layout, so it's not swamped by the parasitic capacitances of the connections.

author: Langdon
author_rank: Frequent Contributor
timestamp: February 17, 2025, 09:35:48 pm
content: You need at least a 10K value for R1 to prevent major power losses (reisitor is connected across VCC and ground almost 50% of the time)This limits the capacitor to a small value.You can lso use a 1N4148 diode an a larger cap, if you like, however.Never use a >50% duty cycle to power a transformer, there is no real benefit.What you are making is an inverter, you can always puchase one too.

author: Zero999
author_rank: Super Contributor
timestamp: February 18, 2025, 06:51:44 pm
content: Quote from: Langdon on February 17, 2025, 09:35:48 pmThat's pretty meaningless without a schematic. Can't you post one? If you struggle with your drawing, then take a screenshot from the 555 data sheet and annotate it using MS Paint, or print it, draw on it and take a photograph.Anyway, a 555 timer won't work very well with a capacitor much smaller than 100pF, yet alone 1.5pF.

author: Langdon
author_rank: Frequent Contributor
timestamp: February 19, 2025, 12:39:33 am
content: Fine.Use a 100pF cap then with a 1N4148.I will post a schematic.