Driving an IV12 Vacuum Fluorescent

[peter bunge]

I need to drive a single IV12 vacuum fluorescent display from a BCD to 7 segment chip.

I could use level shifters like the CD40109B or CD4504B but they don't have 7 devices in one chip (4 and 6) and only drive 18 volts which might work.

I could use a ULN2803 transistor array with 7 pullup resistors on the outputs. The problem is the BCD to 7 decoders (e.g. CD4511) are usually active high, which I need, but the ULN2803 is an inverter which I don't need. A CD4543B might work as the BCD to 7 and can be selected for inverted outputs but it is designed for LCDs not driving transistors.

The  74LS47 has the right polarity to drive the transistor array but it has open collector outputs so 7 more resistors are required.

Any suggestions that don't get even more complicated (shift registers, octal inverters, arduinos, etc)

I'm looking for a convenient driver chip.

[John Rehwinkel]

> I need to drive a single IV12 vacuum fluorescent display from a BCD to 7 segment chip.
> I could use level shifters like the CD40109B or CD4504B but they don't have 7 devices in one chip (4 and 6) and only drive 18 volts which might work.

Maybe a 7446, which can support up to 30 volts?

- John

[David Eustace]

Have you looked at a max6920 or 6921?

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[peter bunge]

Thanks John but the 7446 has active low outputs, the VFD requires active high.

Thanks David but a serial drive is too complicated for my application.

I am investigating the 14543 BCD to 7 driver to see if it will replace the 4511 in my schematic below and is capable of driving the ULN2803.

The ULN2803 lends itself well to using a SIP resistor pullups on the outputs which will minimize the components.

The other picture shows one of my modules for an IN16 Nixie. The tube socket screws are used to mount it. One cable is the BCD and 5v and, in this case, the other is 250v DC. The project is a display of various digital indicators from the past. They look better than a jumble of tubes in a box. So far I have 3 Nixies, a Numitron, an E1T, and a 6LO1i CRT clock working on the chassis. Remaining are an 8453, Dekatron, a couple of Magic Eye tubes, and this VFD display I am working on. I am open to suggestions of affordable additions. I have a few items like a Trochotron that can be added as static displays.

Peter

 

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[David Pye]

Hi Peter,

For my vfd clock project (https://github.com/davidmpye/VFD), I used the following high side driver ICs (I used one per tube but of course I could've multiplexed)

They are either known as UDN2981 and there's also a Toshiba version (TDSsomething).  They aren't BCD though - just one pin per segment, so that might not be any good for your application depending on how many IO pins you have spare ..

David

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[peter bunge]

Thanks Davis; I think I have a solution but will look at your suggestion.

The CD4543 seemed to only drive a milliamp or less but I found I had six MC14543B which will drive 10mA source or sink.

This should do it. I will need to find out what anode voltage I need and choose a power supply, probably running off 5v.

Pin 6 (PHase) sets either active high or active low outputs. It is driven by a square wave for LCD displays. 

I left out that my intention is to add a selection of LEDs that will be in the opening at the front.

I'm off to test the circuit. Peter.

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[David Pye]

Hi,

I ended up using a pair of buck/boost converters to generate 30v for iv11 and the 1.5v for heaters. Driving heaters off 5v and a resistor wastes quite a lot of heat as the current required is quite high so a buck converter is quite a bit more efficient :-)

They are only a few £/USD from eBay/Ali etc.

Happy building!

David

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[gregebert]

I'm contemplating the HV57009 for my upcoming VFD clocks; it requires a negative supply so that presents some challenges but a single device can drive 64 segments at 2mA each.

[peter bunge]

Thanks David; note that the IV12 pin numbers are probably wrong except for the filament and grid. 

I can't read Russian and will find out by trial and error.

Peter

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[peter bunge]

I am only driving one tube otherwise I would use such a chip or the HV5812P-G serial-in which does not seem to need a negative supply. You probably have a good reason for your choice. 

My last schematic has errors which I have corrected below. I did not know the pin numbers for the IV12. These are correct and the display works.

Another error on the first schematic was, after all my talk of polarities, grounding PH instead of pulling it high.

Here is the corrected schematic that works. The filament draws 100mA and I can save over half of that if I need to by using a switching regulator as suggested. This is simpler.

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