On 3/11/12 4:18 PM, Cobra007 wrote:
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.
Then don't turn on the other tube at that time! I turn on only one tube
at a time, which removes that problem.
--
David Forbes, Tucson AZ
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