300V NPN/PNP driver for Nixie tube anode

Thread Starter

South

Joined Apr 7, 2017
28
Hi I just wondered if anybody had experiece in driving NixieTubes?

Attached is an iteration of the design of an anode driver.

In black, the origional and in blue, the updated schematic components.

In red the neccessary supply and current limiting resistor.

I would like to check that this is sensible before testing onthe bench?

SouthCapture of npn-pnp switch 03.PNG
 

schmitt trigger

Joined Jul 12, 2010
497
I see that you have copied an erroneous circuit which is floating around the internet which doesn’t include the resistor between the NPN’s emitter and the PNP’s base.
Keep that.

I don’t see the point for the diode in series with the PNP’s emitter
 

Ian0

Joined Aug 7, 2020
5,507
Nixie tubes have a single anode and multiple cathodes. Why do you want to control the anode? It's usually connected to a 150V to 300V supply with a resistor.
 

Thread Starter

South

Joined Apr 7, 2017
28
Hi All

First things first... that damn diode... it seeemed to do no harm so I included it as the circuit, on the internet, included it and I'm afraid I didn't have the nouce to omit it.

Next the nixi tube striking voltage, perhaps somewhare between 130V and 170V? I maybe need to measure this when my Nixie tube strikes, amongst other readings I need to take to fill in gaps in my knollege.

The Nixie Tube current I would like to say is around 2mA but my lab notes are unclear how I obtained this figure.

I'm sorry, Mr Trigger, but I don't quite follow, are you talking about the PNP's base resistor? I'm sorry if that's not clear, but I now want a 412k resistor connecting the NPN collector to the PNP base.

Ian0... I want to controll the anode because I have six Nixie tubes arranged as a clock, multiplxed to be on only 1/6 th of the time. Showing the time in decimal.

I am planning on constructing the anode control circuit on breadboard and measuring the various, relavent, parameters to see how I should proceed with my project.

I'll do this at the weekend when I'm a little less busy.

Thanks for sparing the time and effort to reply though , I really do appreciate that.

Kind regards

South
 

Ian0

Joined Aug 7, 2020
5,507
I used 3mA, but by the time you have multiplexed them, you will only get a sixth of that on average.
I used TPIC6B595 drivers for them, non-multiplexed.
You are about right with the striking voltage.
The anode driver needs to be able to switch off fast. I would recommend MOSFETs because they switch off faster, or Baker-clamps on bipolar transistors. https://en.wikipedia.org/wiki/Baker_clamp
If they go into saturation they are really slow to switch off, and that would cause ghosting. Sometimes you can't strike a segment if there is already a segment conducting, because it drags the anode down to below the striking voltage.
 

Thread Starter

South

Joined Apr 7, 2017
28
Hi Ian,

I reckon 3mA is about right for a tube.

I really like your idea of using shift-registers. It would save a lot of problems!

Unfortuneately I have already designed and built my multiplexed clock!

I am, at present, upgrading the anode switches.

For completeness I'll look into suitable, SOT-23, SMD, high voltage MOSFETs.

I think pretty much I could substitute a MOSFET for a BJT as they are both similar footprints?

I'd have to adjust the biasing but it could perhaps be done?

I'll have to double check as I have already made the PCB and that can't really be changed at this stage.

I'm also thinking that as i'm multiplexing; the whole display will be six times dimmer than driving the tubes constantly?

So research is needed!

South
 
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