Can I drive the INS-1 neon bulb with the SN74141 or KM155ID1 chip?

[Chaos Hydra]

Hello! First time post here. So I am doing a nixie clock with IN-12 and KM155ID1 mux chip. To ensure the look, I decided to use INS-1 neon bulb to do the little colons between the digits. My questions is: can I drive the INS-1 bulb as I did to IN-12? With an 220k current limiting resistor under 170VDC, the INS bulb got 5mA. Considering IN-12 has 6mA without current limiting resistor, I think I can just use K155ID1 to sink in the current and control the neon bulbs.
Consider I give most of my knowledge of digital parts' parameter back to professors, can any one please point out on the data sheet: when I am sinking current into the active low pin(to turn on an bulb or a single filament in nixie), which value is the maximum current?
Very appreciate the help here!

[John Rehwinkel]

On Apr 18, 2015, at 4:06 AM, Chaos Hydra <erguo...@gmail.com> wrote:

> Hello! First time post here. So I am doing a nixie clock with IN-12 and KM155ID1 mux chip.

The KM155ID1 is a nixie driver, not really a "mux chip", although it can certainly be used in multiplex designs.

> To ensure the look, I decided to use INS-1 neon bulb to do the little colons between the digits. My questions is: can I drive the INS-1 bulb as I did to IN-12? With an 220k current limiting resistor under 170VDC, the INS bulb got 5mA. Considering IN-12 has 6mA without current limiting resistor, I think I can just use K155ID1 to sink in the current and control the neon bulbs.

Yes, the chip won't mind at all. However, due to the clamp diodes, the "off" voltage is about 100V (60V for the US equivalent). With an ordinary nixie this is fine as long as another cathode is lit. However,
for individual bulbs and nixies without any cathodes lit, that's enough voltage across the tube to possibly cause some unwanted glow.

> Consider I give most of my knowledge of digital parts' parameter back to professors, can any one please point out on the data sheet: when I am sinking current into the active low pin(to turn on an bulb or a single filament in nixie), which value is the maximum current?

That does not appear to be given on the data sheet, however, it does say that when sinking 7mA, the voltage on an output pin will not exceed 2.5V, so 7mA is allowed by implication.

- John

[Chaos Hydra]

Thanks John! That is very helpful!
 So to avoid unwanted lit, what should I do? Can I just put a diode there to prevent the chip sourcing the bulb?

[threeneurons]

If you want to light up a neon bulb, with that chip, add an extra 220K resistor. Hook it up in parallel with the neon bulb. That should keep any leakage current, when off, from hitting a level to fire the neon. 

[Chaos Hydra]

Thanks! trying it right now!

[Chaos Hydra]

That totally worked! but I did the wiring when the 170v is on, and got zapped, threw  my only 220k ohm to nowhere. DAW!!!!

[gregebert]

I suggest you add a power-on indicator; it only requires a few milliwatts and it could save your life.

Also, it's wise to put a large resistor across each DC supply to discharge the capacitors, especially the HV ones, when the power is off. Nixies will extinguish around 120-150V, so just because they are dark does NOT mean it's safe to go poking around. A 100K 1/2 watt resistor can be used for supplies up to about 200V. At higher voltages it becomes a tradeoff of wasted power vs. discharge time.

The discharge time is about 5 time constants, so T=5RC, where T is in seconds, R is in ohms and C is in Farads. Sometimes it's easier to use megohms & uF.

I've gotten ultra paranoid with my next project ( bench power supply for nixies & dekatrons), so each HV cap in the HV tripler has it's own fuse, reverse-polarity diode, bleeder resistor, and neon-bulb to indicate dangerous voltage (>60V).