VFD Clock Design Feedback - Page 1
Forum section: electronics / projects

author: MrChzl
author_rank: Newbie
timestamp: January 28, 2018, 02:52:19 pm
content: Over the last year I have been designing a VFD Clock to give as a gift to friends and family. I was hoping to get some feedback on my design being the first time I've ever used an EDA. I do know that running VFD's on DC is the "quick and dirty" way of powering them, but keep in mind this project was supposed to be done by last Christmas, however that deadline has come and passed. Designed in KiCad. All feedback welcome!

author: Rolo
author_rank: Regular Contributor
timestamp: January 28, 2018, 05:47:41 pm
content: I like VFD displays so this topic caught my attention, but I do not use Kicad so can't view your project. I did find an online kicad viewer but that showed three pages, two with many switches and one with some sort of module. No VFD found. I think the viewer is showing a different project.Could you give some more info?

author: Macbeth
author_rank: Super Contributor
timestamp: January 28, 2018, 07:14:41 pm
content: Even with KiCad I got a load of missing library/component errors.You should really upload the schematic in PDF form (use the Plot option in KiCad to generate it)

author: MrChzl
author_rank: Newbie
timestamp: January 30, 2018, 02:01:07 am
content: Plotted out in PDF Format. Thanks a bunch for taking a look!

author: edavid
author_rank: Super Contributor
timestamp: January 30, 2018, 02:38:25 am
content: 1. The PNP drivers won't work as shown.2. If you drive the filaments that way, you will have a substantial voltage gradient, perhaps too much to compensate for with PWM.3. Don't make us calculate the supply voltages.

author: MrChzl
author_rank: Newbie
timestamp: January 30, 2018, 03:01:53 am
content: Quote from: edavid on January 30, 2018, 02:38:25 am1. A little feedback on why the PNP drivers wouldnt work would be great so I can learn from erroneous design.2. Filaments ran in series, so supply voltage divided by number of displays should net 1.18V per filament. Would I have to calculate voltage drop per display and adjust accordingly, then wouldn't filament #1 burn right up upon powering?3. 30V Grid, 30V Anode, 7.2V Filament.If I'm doing something wrong (besides driving VFD's on DC) maybe you could give me some feedback, or even point me in a direction where I could learn...

author: edavid
author_rank: Super Contributor
timestamp: January 30, 2018, 03:31:35 am
content: Quote from: MrChzl on January 30, 2018, 03:01:53 amPNP emitter has to be more positive than collector to functionYou need to use common emitter mode for a PNP level shifter, but you would also need voltage dividers for the bases, or use extra NPNs as level shifters, or just buy some VFD driver ICs...QuoteNot what I'm talking about... the voltage gradient across the filaments creates a brightness gradient.https://www.futaba.co.jp/en/display/vfdinfo/vinfo_kudo_1.htmlhttps://www.noritake-elec.com/technology/general-technical-information/vfd-operationQuoteWhy the separate grid and anode regulators?Also, you probably want to use a separate supply voltage or DC-DC converter for the filaments, to save power.

author: floobydust
author_rank: Super Contributor
timestamp: January 30, 2018, 04:16:09 am
content: I thought you need a -ve grid-cathode voltage to turn off a digit. That might be where the PNP's (emitter) came from. IV-22 datasheets are hard to read in Cyrillicand I don't know the tube well.I use a dedicated filament transformer with the center tap going to a -ve bias supply. This also lowers the brightness gradient, you can't really see it. Each digit appears the same brightness; whereas OP's circuit from right to left digits is dimmest to brightest due to each filament having a different potential wrt to ground.