I mentioned 300V because that was the rating of the transistors. Cobra, the DMMT5551S would actually work very well for my IN12 driving application, and I also appreciate the bases being on one side, thanks for helping me discover this component! -Paul
On Mar 11, 11:06 pm, David Forbes <[email protected]> wrote: > On 3/11/12 4:44 PM, Cobra007 wrote: > > > > > > > > > > > > >> Then don't turn on the other tube at that time! I turn on only one tube > >> at a time, which removes that problem. > > > That is not completely true, it's not that I turn on both tubes at the > > same time, it is because the current starts to flow through the wrong > > tube because IT CAN. With a 170V anode voltage and a 50V clamping > > zener, the minimum voltage on either of the tubes (on or off) is 120V. > > A tube that has 120V, is switched off but was switched on just a > > fraction earlier (due to multiplexing) will leak current from anode to > > ground through the zener clamping diode. You can't stop that unless > > you disconnect the anode from the HV power supply, through an extra > > transistor or something else. > > > I agree that adding complexity will in most cases reduce the > > reliability. In my case, it is not so much that the circuit becomes > > more complex (replacing 8 transistors in 1 package by 8 discrete > > transistors) it is more an increase in PCB complexity. So I am not > > worried that it will decrease the reliability. > > > Michel > > I am confused. If you are turning off one tube then turning on the other > tube, and operating at a low duty cycle (I assume you're still > discussing the dimmed case), then there will be a long delay between > turning off the first tube and turning on the second tube. So the first > tube should have time to deionize. Is the leakage strong enough to make > a glow? For how long? > > My Nixie watch displays an interesting result when one tube is broken - > the other tube will light all cathodes faintly when the broken tube is > selected. That's because all the cathodes are clamped to 50V, but the > power supply makes about 200V to an open circuit. (I connect both anodes > directly to HV without resistors.) In that case, the tube is lighting > when it shouldn't. But there is a broken tube, so there's no reason to > make the display function properly in that case. > > I provide display blanking in my watch, which is accomplished by feeding > an MPU output to the HV supply feedback node through a carefully-chosen > resistor, which makes the HV drop to 110V when the bit is set to 1. This > allows me to turn off the display and not excite the case described > above in normal operation. It's a very low cost solution to blanking, as > I share the MPU pin with the accelerometer enable. > > The long and short of it is that you ought to be able to use a 50V > driver chip in a two-tube design with a bit of effort. > > -- > David Forbes, Tucson AZ -- 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.
