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Electronics => Projects, Designs, and Technical Stuff => Topic started by: thefatmoop on October 19, 2021, 04:00:51 pm

Title: Vacuum fluorescent display multiplexing -- max current?
Post by: thefatmoop on October 19, 2021, 04:00:51 pm
Hi all,

I've purchased a few IV-4 16 segment display tubes. I've got an MCU running a boost converter and using the tube grids to multiplex.

Question - with 5 tubes multiplexed, my max brightness when driving at the rated current is ~1/5th compared to static driving the tubes at their rated current. Does it put additional wear on the fluorescent material if I just crank up the anode segment voltage, so that the average current is the same as it were for static drive at rated current?

Question2 - Running the grids at the same voltage as the anodes creates illumination hot spots (even when running far below rated currents/voltage). I haven't found much information on this sort of problem mentioned elsewhere. Running the girds at let's say 12v where anodes are at 30v decreases overall brightness but removes shadows. Any thoughts on this?
Title: Re: Vacuum fluorescent display multiplexing -- max current?
Post by: David Hess on October 19, 2021, 08:38:35 pm
I checked a few datasheets and VFDs intended for multiplexing include a duty cycle specification, which I assume means that you must remain within the given maximum current specification.
Title: Re: Vacuum fluorescent display multiplexing -- max current?
Post by: thefatmoop on October 20, 2021, 02:11:58 am
Yeah IV-4 has no mention in the translated datasheets i've found. I think you're right. Likely it's how hard electrons are hitting (voltage) the fluorescent material that breaks it down early.
Title: Re: Vacuum fluorescent display multiplexing -- max current?
Post by: David Hess on October 21, 2021, 03:24:35 am
Yeah IV-4 has no mention in the translated datasheets i've found. I think you're right. Likely it's how hard electrons are hitting (voltage) the fluorescent material that breaks it down early.

That would be the anode voltage and not the anode current.
Title: Re: Vacuum fluorescent display multiplexing -- max current?
Post by: thefatmoop on October 21, 2021, 08:16:59 pm
number of electrons hitting = current
individual electrons 'speed' = voltage

Anyway I found the official datasheet and found another post that clarified things. The IV-4 tubes in static drive = 25v anode, but in 'pulsed' (multiplexing) mode, they allow up to 50v on anodes with a duty equation mentioned. FYI for anyone in the future building with these great little tubes.