Power Supply Waveform for VFD - Page 1
Forum section: electronics / projects

author: jazawe
author_rank: Newbie
timestamp: September 02, 2022, 07:17:23 pm
content: I recently found a cool dot-matrix VFD that I would like to use as a display for a project that I'm working on. Its part number is MN12864k. I'm confident that I can write the necessary driver code, but I'm having trouble deciphering the requirements for the filament power supply.The part has 2 useful data sheets:-https://d1.amobbs.com/bbs_upload782111/files_49/ourdev_704971DI6NU6.pdf-https://img.jdzj.com/UserDocument/2017y/wenzihui/dn/zl7968.pdfAnd this page has some information that's intended to be helpful, but that I'm struggling to understand the meaning of:-https://www.noritake-elec.com/technology/general-technical-information/vfd-operationIt looks like the filament wants an ac voltage at somewhere between 10khz to 200khz. According to the data sheet, the voltage needs to be 3vac biased to 4v. If you go to the noritake website link and look at section 5.3 (Pulse Filament Drive), it seems to imply that the RMS voltage of the filament should be calculated relative to the bias voltage. All these things together seems to tell me that I should drive the filament with a 10khz-200khz square wave with a minimum voltage of 1 volt, and maximum of 7 volts (4-3 to 4+3). However, the page also states:"A 1/2 duty factor should be set, and the peak to peak pulse wave form should be 1.5 times or less than the RMS value."I have absolutely no idea what this means. It would be super helpful if somebody more knowledgable about VFDs provide some insight.Thanks!

author: Terry Bites
author_rank: Super Contributor
timestamp: September 04, 2022, 10:18:34 am
content: The filament will operate happily on 3v (RMS) 50/ 60Hz . DC won't work unless you have a custom VFD made.You can, if you want, drive the filament from a pwm waveform if you want variable brighness .The pulse frequency is not critical. Varying the duty cycle sets an RMS voltage as per their explanation.Note the bipolar pulse.Its a lot of expense faff if you dont need it.All you need is a small transformer. Or an AC converter if there is no DC available. Eg An audio power amp driven by an LF oscillator. PAM8302A? You might be able to add a phase shift network from output to input to make it self oscillate.seehttps://www.eevblog.com/forum/projects/vfd-filament-power-using-lm4871-replacement-for-obsolete-lm9022/

author: macboy
author_rank: Super Contributor
timestamp: September 04, 2022, 03:31:24 pm
content: Honestly I understand the desire to use this display. Nothing else comes close to the unique and beautiful VFD look. But I would seriously consider buying a display with built in driver. Noritake makes many of these. It is the same chip on glass display you have, but mounted on a board with a microcontroller programmed to drive the display. They have a frame buffer, built in fonts and graphics commands, and do all the work of row column updates 70 times per second. And they have the required power supplies built in, usually boosting from a single 5v input.Making this raw display of yours actually display anything useful is an entire project in itself. That's fine if it is what you want to do, but if what you want is a display for a project (and not a display that is a project) then just buy a module. Look on eBay, NOS displays show up pretty frequently. A well used one may work but will likely have burn in.