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/53E9306E.3010303%40blinkenarea.org. For more options, visit https://groups.google.com/d/optout.
