> > A fine way to achieve the PWM dimming you want with a low-voltage Nixie > driver is to have a current measurement device in the power supply's > feedback path, which is conveniently provided from the common emitter > terminal of the TD62083 (ULN2083).
I think this is what you have done in your nixie watch. It will effectively increase the anode voltage until ionization has taken place. > > You can detect when the tube begins to ionize by sensing the current > using a comparator such as an LM339 working across a small resistor to > make <1V drop from emitter to B-, and use this time to start the on-time > countdown in the PWM dimming code. You then have to reduce the OFF time > after that pulse by the measured ionization delay. In this case I would need 2 comparators to distinguish through which tube the current flows because the current will flow but it will flow through the wrong tube. I can see my anode voltage rise to 170V but the tube doesn't light up, as there if no reason the voltage rise should stop at 170V, the only explanation is that the current starts to flow through the wrong tube. I have measured that current can flow through the nixie down to about 120V. Interestingly, 120V + 50V zener is exactly the 170V that I measure at my anode voltage. And then, after I have detected that the current flows through the wrong tube, there is nothing I can do about it unless I add more circuitry to be able to stop the current flowing through the wrong tube. > > The advantage of this method is that it will produce a more uniform > brightness in your dimmed display, since you are guaranteed that the > ionization time is taken into account. Plus, you can use the small, > low-cost driver chips. > If all these features are added, it will probably produce a more uniform brightness, but I can see from the amount of PCB space that I have left over that it is not going to fit :-). Michel -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
