Thanks a LOT Anne! I'm finally understanding that it's sort of like an LED! To test if I understand it properly, would I be correct if I simply connect the nixies to 180v and use a BJT current limiter to limit the current to 2mA?
On Monday, 11 August 2014 22:06:57 UTC+1, Arne Rossius wrote: > > Hi, > > 'Alaba Baju' via neonixie-l wrote: > > I understand the IN-1 needs about 170v to light up and about 133v to > > stay on. One thing I've noticed though is that most people only seem > > to build switching supplies for the higher voltage. I don't > > understand! > > The higher voltage (ionization voltage) is the *minimum* voltage your > power supply needs to provide. If the output voltage of your power > supply is lower, the tubes may not light up at all. The lower voltage is > the (approximate) voltage at the tube anode when the tube is on, similar > to an LED's forward voltage. You use a resistor between the voltage > supply and the tube's anode to get these two voltages automatically. > When the tube is off, (almost) no current is flowing so the resistor > doesn't drop any voltage, and the full power supply voltage is available > at the anode. Once the gas ionizes and the tube lights up, it starts > drawing current, thus dropping voltage across the resistor. In effect, > the difference between the two voltages is dropped across the resistor, > and you don't have to do any switching. > > A simple way to approximate the resistor value is this: > > R = (V_supply - V_sustain) / I > > where V_supply is your power supply voltage (may be higher than 170V), > V_sustain is the tube's sustaining voltage (133V) and I is the desired > current (a typical or maximum value can usually be found in the tube's > datasheet). > > The formula isn't quite exact because the sustaining voltage will be > dependent on I, but it is good enough to get an idea for the correct > anode resistor value. If you are unsure, start with a high resistance > and measure the current. > > If you use a lower current than the datasheet recommends, the tube life > will be prolonged but the digits will be less bright (obviously) or not > light up completely. Some datasheets also list a minimum current for > this reason. > > In my nixie clock with four NL-840 tubes, I used a 180V power supply > with 18k anode resistors (one for each tube). The datasheet recommends > 10k at 170V and 47k at 250V. From that, we get I = 2.2 mA and > V_sustain = 148V, so with my 18k resistors the current should be about > 1.8 mA, just above the minimum value of 1.5 mA and well below the > maximum value of 3.5 mA. > > > HTH, > Arne > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/3dcd6a4a-e7f6-49fa-b2d3-4c3b5b2ea108%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
