[neonixie-l] Re: Constant current source design

[gregebert]

Assuming you have high-enough HV power-supply headroom for the nixies (180V 
or more), the choice for the resistor begins with the isolated power 
supply; I chose 12V because there are a lot of small, efficient DC-DC 
converters that provide 12V. You can use other values, but be careful to 
stay below the rated Vgs(max). 

Next, you want some adjustment range for the anode current. I set the 
nominal gate voltage at 10V. That gives +/- 2V of range to adjust the anode 
current without changing resistors.

Next, from the datasheet, you need to find Vgs(on) for the MOSFET. It's 
usually plotted on a curve. For the FQD7P20TM that I use, it's about 4V 
(see the transfer characteristics curve).

Next, you need the target anode current. For a Burroughs 5092, it's 2.2mA.

The voltage-drop across the resistor is 10V - Vgs(on); in this case, it's 
6V. Now you can solve for the resistor value:
   R=V/I= 6/0.0022   = 2727 ohms. The nearest standard value = 2.7K.

Sanity-check the power in the resistor: P=I^2R; in this case,  P=13mW, so 
even with tiny surface-mount devices you are fine.

You should also sanity-check the PMOS transistor worst-case power 
dissipation. Assume a ridiculously low nixie voltage of 125V. The voltage 
across the PMOS is Supply_voltage - Nixie_voltage - Resistor_voltage = 
200-125-6.

PMOS power = Max voltage * typical current = 69*0.0022 = 150mW.

This device has a Theta j-a of 110C/W, so the temp-rise = 110*0.15 = 17 
degrees. Plenty of margin here.

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[neonixie-l] Re: IV-1 datasheet English translation

[Paul Andrews]

I 'paraphrased' much of the literal translation e.g. 'Max' instead of 'not 
greater'. The translator completely failed to translate Накала, though it gave 
the Roman alphabet equivalent of Nacala. From the context it was fairly clear 
that it is the filament, which I translated as heater. 'Incandescent' was the 
closest I could get at the time, though I am seeing things like накаливания 
being translated as both 'filament lamp' and 'incandescent bulb'. 

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[neonixie-l] Re: Constant current source design

[Paul Andrews]

Hi (Greg?),

Using the datasheet for the PMOS transistor you use in your circuit, how do 
you calculate the value of R116 (the resistor between +200V and the source 
of your MOSFET)?

On Saturday, March 25, 2017 at 12:30:53 PM UTC-4, gregebert wrote:
>
> That's basically what I use in my designs. I'll highlight the differences:
>
>- I use a PMOS instead of PNP, mainly because it requires no 
>drive-current.
>- R1 & R2 are replaced with a pot to make the current adjustable.
>- The above pot can driven from a small DC-DC converter (my 
>preference), or between the HV supply & GND. There's essentially zero 
>current for PMOS gate-drive, so high resistance values are fine. Not the 
>case with PNP, though, due to finite base-currrent.
>- A zener diode is added to clamp any spikes that may arise at the 
>gate of the PMOS device. It's a paranoia item.
>- A filter cap was added, in case there is unexpected noise from the 
>DC DC converter, and also to suppress any very-short transient that may 
>arise that are too fast for the zener to kick-in. (paranoia item).
>- A large resistor across the PMOS to bleed any potential ESD. Without 
>it, there is a remote possibility of charge-buildup. (paranoia item)
>
> So, this circuit is replicated for each anode. When multiple anodes are 
> driven, they all share the same gate-drive signal, which I call PDRV on the 
> attached schematic.
>
>
>

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[neonixie-l] Re: EEV blog on Nixies

[GastonP]

Hey! 
"Our" Mike got some air time!
Get ready for a surge on requests :)

On Monday, May 8, 2017 at 11:25:19 PM UTC-3, Pramanicin wrote:
>
> For those of you who haven't seen this, the crazy Ozzie has a 5 part video 
> blog on his channel about an 8 digit IN12 nixie tube project that I'm 
> currently watchinggood stuff (as usual)..
>
> https://www.youtube.com/watch?ev=7uogKucrPks 
> 
>
> Cheers,
>
> Nick (the Pharma one..)
>

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