Easy way to drive vacuum floroescent displays that is glass only - Page 1
Forum section: electronics / beginners

author: alank2
author_rank: Super Contributor
timestamp: June 24, 2016, 11:45:29 pm
content: Hi Everyone,I got one of the $3 samsung vfd's from elecrow that has nine 7 segment numbers in it. I was able to make it work and figure out its pinout by hooking 2.5V DC across the filament and feeding 12V to the grid and segments.My question is - what easy, low part count, cheap circuits can be used to generate 12V from 5V. Doesn't need to be much current, I think the 12V was only a few mA while the filament was 100mA.Also, the filament is supposed to be AC, any ideas for the same, easy, low part count, cheap circuit to make a voltage AC drive for the filament?Thanks,Alan

author: Signal32
author_rank: Frequent Contributor
timestamp: June 25, 2016, 03:27:02 am
content: 5v->12v : It doesn't get much simpler than using the MT3608 boost converter chip ( See schematic attached, also schematic in the datasheet ).Or perhaps you'dd wanna use a ready-made solution like this:http://www.aliexpress.com/item/B0512S-1W-Free-shipping/32588489712.htmlhttp://www.digikey.com/product-detail/en/recom-power/ROE-0512S/ROE-0512S-ND/5684098For VFD, I think a center tapped transformer is recommended, This would also work:https://threeneurons.files.wordpress.com/2011/09/lm1877_vfd.gifNot sure what are the disadvantages though.

author: alank2
author_rank: Super Contributor
timestamp: June 25, 2016, 04:02:19 pm
content: Thanks - I appreciate it.

author: alank2
author_rank: Super Contributor
timestamp: June 25, 2016, 04:18:48 pm
content: I don't see the MT3608 at digikey/mouser - is there an equivalent?

author: bktemp
author_rank: Super Contributor
timestamp: June 25, 2016, 04:41:34 pm
content: Generating 12V is the easiest task when driving a VFD, even the old 34063 can be used.For 9 7 segment displays you need 9+7 = 16 lines capable of driving at least +15V. 12V may be enough if driven static, but you need to multiplex them at 1/9 ratio. For a decent brightness the voltage needs to be higher. From my experience 15V is the lowest useful voltage, for full brightness the voltage should be around 20-30V.If you can get one of those, that should be the easiest solution:http://www.princeton.com.tw/en-us/products/displaydriveric/vfddrivercontrolleric.aspxGenerating the AC signal for the filament can be done using a simple transistor H-brige. If you can tolerate a bit of non uniformity in brightness, you can even use DC. The positive end will be a bit darker than the negative end, but it does not harm the display.

author: Signal32
author_rank: Frequent Contributor
timestamp: June 25, 2016, 05:00:51 pm
content: Quote from: alank2 on June 25, 2016, 04:18:48 pmhttp://www.ti.com/lit/ds/symlink/lmr64010.pdfhttp://www.semtech.com/images/datasheet/sc4503.pdfhttp://ww1.microchip.com/downloads/en/DeviceDoc/mic2619.pdf

author: Yansi
author_rank: Super Contributor
timestamp: June 25, 2016, 05:12:00 pm
content: Find a suitable VFD driver chip. There is a shitton of them :-)For example the oooold well known "6312" made by almost all chip vendors, including Princeton, ST, ....There is also a bunch of high voltage shift registers from Texas, for example 75518, TL4810, ...

author: Gyro
author_rank: Super Contributor
timestamp: June 25, 2016, 07:14:39 pm
content: Quote from: bktemp on June 25, 2016, 04:41:34 pmI thought it was more common apply negative bias to the filament so that the segment and grid drives are at sensible logic levels.For the filament supply, if whatever you're building is mains powered then a small isolated winding added to a mains transformer is the simplest, and easiest to apply a -ve DC bias to.

author: bktemp
author_rank: Super Contributor
timestamp: June 25, 2016, 07:48:19 pm
content: Quote from: Gyro on June 25, 2016, 07:14:39 pmUsing a negative voltage simplifies the level shifter, because you only need PNP/PMOS transistors capable of >20V switching the segments/grids between high impedance (with pulldown to the negative voltage) and the logic voltage (3.3V or 5V). This is often used when VFD drivers are integrated into microcontrollers or clock ics.If you have a centre tapped transformer for the filament this is probably a bit easier/cheaper, but if you want to power everything from +5V or +12V true level shifters and a positive grid/segment voltage are often used, because you can drive the filament from the DC voltage without using a transformer.Almost every dedicated VFD driver ic I have seen used a positive voltage.

author: janoc
author_rank: Super Contributor
timestamp: June 26, 2016, 09:39:30 pm
content: Here is a good circuit for driving the filament using AC voltage and center tapped transformer:http://www.kerrywong.com/2013/06/05/vfd-filament-driver-using-555/Very simple, works well and you can always add an extra winding for 12V if needed.He has also a full description of a discrete driver circuit, you can certainly steal a few ideas from there:http://www.kerrywong.com/2013/06/13/a-diy-vacuum-fluorescent-display-driver/