Please count me in! I have a stagnated project to drive these large displays - I already made a smart socket to actually switch the segments using opto triacs and that works well - I have also used a bunch of small EL-Wire power supplies which sort of worked OK but it has not gone any further - I am interested to see how your power supply ends up driving the displays. - Richard
On Monday, 4 May 2026 at 19:38:47 UTC+1 gregebert wrote: > *UPDATE*: After a lot of tradeoff analysis, simulations, etc I have > decided to use an H-bridge to create the triangular waveform. Segments will > be controlled by opto-triacs. > > An electroluminescent display is basically a "light emitting capacitor". > > *Why an H-bridge* ?? Electroluminescent displays require an AC supply > around 1 kHz. Lower frequencies, such as 400Hz, will work but require more > voltage, which puts dielectric stress on the display. Higher frequencies > can reduce the voltage for a desired brightness. This is in line with their > capacitor-like construction. I could have used a sinusoidal oscillator and > driven a power transformer, but I've already done 2 previous designs with > high-frequency step-up and ran into a lot of problems on the bench because > it wasn't possible to accurately simulate the design under all load > conditions. The H-bridge is well-behaved in simulations, and they match > reality pretty well. This is a non-symmetric H-bridge: The "pullup" parts > are just a simple on/off switch (NPN) transistor, while the pulldown parts > have variable strength. Due to the high operating voltage, NPN devices had > to be used because there aren't any readily-available PNPs rated above 700V > that also have adequate safe-operating area (SOA) characteristics. Even > finding the NPNs was a bit of a hunt. MOSFETs at that voltage have too much > leakage current. > > *Why a triangular wave* ?? Applying a triangular wave to an > electroluminescent display results in constant current. The H-bridge has > 7-levels of binary-weighted programmable pulldown current (16uA to 2mA per > bit), which will drive up to 8 IEL-0-IV displays. There are options to > drive up to 40mA to handle up to 6 of the large I-195 displays. It's > actually easier to generate a triangular wave than a sinusoid. The current > needs to be adjusted based on how many segments are driven (load > capacitance). > > *Why opto-triacs* ?? I need bidirectional current control, so that > rules-out simple transistor/MOSFET control. Traditional triacs will work, > but because of the way the H-bridge is built, the driver for the > opto-triac is much simpler than for a traditional gate-driven triac. > > So, the design is being captured in KiCad and simulated in SPICE (analog) > and Verilog (digital) as I inch forward. > > On Wednesday, March 11, 2026 at 1:55:43 PM UTC-7 Mac Doktor wrote: > >> On Mar 11, 2026, at 4:50 PM, Sture Nystrom <[email protected]> wrote: >> >> As fair I can remember the lifetime is not so long on a EL display. >> >> >> IIRC, like many technologies EL phosphors have a half-life related >> directly to how hard they’re driven but compared to others it’s really >> short. >> >> >> Terry Bowman, KA4HJH >> "The Mac Doctor" >> >> https://www.astarcloseup.com >> >> "If only you could see what I've seen with your eyes."—Roy Batty, *Blade >> Runner* >> >> -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/7a865818-043e-4148-ab6e-bd8bc99e57e3n%40googlegroups.com.
