On Monday, March 5, 2018 at 7:14:56 AM UTC, gregebert wrote: > The MAXIM device uses BiCMOS technology, so the I/O pins are > probably NPN devices and should be more tolerant of voltages above > 76 VDC.
I'd prefer not to allow the voltage to rise that far. 70 volts seems to be enough to reliably blank all the cathodes on the couple of tubes I tested. The data sheet I have says the output stage consists of a push-pull pair of N and P channel FETs. A switched-on FET will conduct current in both directions; even a switched-off FET has a body diode that will start to conduct 700mV or so above the rail. There may well be protection diodes in there too. So I expect the chip to be capable of sinking a few uA of current back from its outputs into the positive rail, and testing seems to confirm that this works. > It's best to follow the datasheet for all possible operating > conditions, but I think you could use a bleeder resistor across the > MAX6921 pins and GND. I'm honestly not convinced that this is necessary. I think the driver can handle the leakage on its own while staying within its specified operating range. > First, measure the leakage voltage on all of your nixie tubes with a > DMM that has an input impedance of 10Megs. Basically, connect the > anode of the nixie tube to the anode supply, and measure the voltage > at all 10 cathodes to GND. If it's significantly lower than 76 volts > and you get no noticeable glowing on the tube, you can use a 10Meg > bleeder resistor. A 10 meg meter reads ~60V (so it's drawing 6uA) and just starts to light the tube ever so slightly. The leakage current at 70V will presumably be significantly less, though I don't have the equipment to measure it easily. I don't think this is going to stress the driver too much. (This does prove that I have to be careful using my multimeter to measure these voltages, though!) Mike -- 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 neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to firstname.lastname@example.org. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/fc4b9beb-a76d-49cf-8752-d0745706dc4a%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.