Author Topic: Showing my VFD PSU  (Read 2439 times)

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Offline Rolo

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Showing my VFD PSU
« on: June 15, 2018, 05:26:02 pm »
I Like to show my current project, it's a PSU for VFD display's.
The PSU is for multiple digits VFD display's. It pretents to be a universal as in it's adjustable for different types of display's.
It contains a filament driver section with the LM4871. This is an audio driver by name but it's the same as the
(now out of production) LM9022 Filament driver. This driver is in self oscillating mode at arround 27 KHz.
Second part is a high freq. switcher (LM2733Y) for the high voltage. It goes up to 40V on a 5V input.

The filament driver is AC coupled and has a virtual center tap that is raised from the ground by a zener diode.
Inspiration for this design comes from the Noritake VFD fundamentals guide : https://www.noritake-itron.jp/eng/cs/appnote/apf100_vfd/index.html
The PSU runs on 5V DC, the filament and the HV can be enabled/disabled by a microcontroller.
Low on HV-PD shuts down the HV switcher, HV output goes to Vin (5V) when disabled. High on FIL-SD shuts down the filament.
This high can range from 3.3v to 5V so it's compatible with 3.3V controllers.
Shutting down the filament saves the lifetime of the VDF display when the controller has a power-save function.

If you leave the shut-down inputs not connected the filament and HV are both on. Easy for experimenting.
The filament power can be adjusted for different VFD display's by changing R7 and R10, this are 1206 type resistors.
R8 and R11 have to be about 5 times the hot resistance of the filament. (Got this bit of information from member Ian.M)
The HV output can be adjusted bij changing R2 and R13, I choose two in resistors in series here to get more values using the standard E values. See the LM2733 datasheet for specs and calculations on Vout and the value of C1.
I have made a PCB design in Diptrace and assembled one today, it's going to be used with a 8 digit dot matrix VFD.
Made some quick pictures of the 8 char display I'm working with now, also have a 13 char laying arround. That will be the next one that gets this PSU. Also want to make a graph about the filament output with different loads. To be continued.
 











« Last Edit: June 15, 2018, 05:47:06 pm by Rolo »
 
The following users thanked this post: Sparky49, Ian.M, NivagSwerdna, Sputnik7

Offline apblog

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Re: Showing my VFD PSU
« Reply #1 on: June 17, 2018, 02:54:30 am »
Thanks for posting this.  I am definitely going to add this to the list of things to review when I start my own VFD project soon.
 

Offline Rolo

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Re: Showing my VFD PSU
« Reply #2 on: July 04, 2018, 07:27:13 pm »
The 13 character display is working now, it has it's own serial board and VFD PSU. In real life the contrast is much better, my phone can't handle the brighness very well.





 

Offline luiz10000

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Re: Showing my VFD PSU
« Reply #3 on: May 01, 2019, 05:56:42 pm »
hello, thank you for this circuit. I assembled one and it is working (I did not connect yet to my 16dig vfd) .... but are really c7/c8 1 microfarad capacitor? The ones in your photo are so small to be 1uF!!
 

Offline Rolo

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Re: Showing my VFD PSU
« Reply #4 on: May 01, 2019, 06:07:40 pm »
Yes, they are 0805 sized 1uF caps. Where did you get the LM4871? I'm asking because there a fake's arround that do work but have lower output power then the original chips. This can be an issue on VFD's with longer filaments (like your 16 digit model). I  have both chips so can post what's printed on them if you need that info.
 
« Last Edit: May 01, 2019, 06:24:40 pm by Rolo »
 

Offline archeocomp

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Re: Showing my VFD PSU
« Reply #5 on: October 05, 2019, 07:59:45 pm »
Hi Rolo, do you still have datasheet for that VFD display? I can't find it anywhere.
« Last Edit: October 06, 2019, 06:34:00 am by archeocomp »
 

Offline Rolo

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Re: Showing my VFD PSU
« Reply #6 on: October 06, 2019, 06:41:26 am »
I do not have a real datasheet, the seller listed some printscreens of a datasheet, I extracted a PDF from that. It does not give the pinout but that's easy to find out. I will PM you some info.
 


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