W dniu piątek, 19 stycznia 2018 19:01:52 UTC+1 użytkownik Jon napisał: > > Tomasz - which nixies are you using in this application? I seem to > remember some discussion from years ago that some tubes (maybe ZM1000?) > were particularly prone to ghosting and leakage effects even at microamp > currents. > > Jon. > B-5445
W dniu piątek, 19 stycznia 2018 19:02:23 UTC+1 użytkownik Frank Bemelman napisał: > > And use a 50/50 divider, to make the voltage between anode and cathode of > the tube as low as possible. Do not set it at 120V, but go for 90V, using > equal resistors. If your HV is higher than 180V, try reducing that to at > least 180V or perhaps 170V. > Actually I did use same value resistors, but the current from cathodes is big enough to make a difference. I used high valued resistors, though - 470k. I have only 0805 resistors and I don't want to fry them. I'll doodle around to get the real voltage at 90V and also check what will happen at 60V. W dniu piątek, 19 stycznia 2018 21:29:20 UTC+1 użytkownik gregebert napisał: > > From the datasheet, collector leakage current is about 100nA. Assuming all > of the NPN leakage current is amplified in the PNP, you would get 4-5uA of > actual leakage to the anode from the PNP. That doesn't seem like enough > current to me to cause a visible glow in a nixie. > > Your scope probe (10meg) will "pull" 5uA of leakage current down to 50V. > You can do a quick leakage test on the PNP by disconnecting the nixie > anode, and any bleeder resistors, and measure the voltage at the PNP's > collector when it's off (but while your power supply is on, of course). You > should measure substantially less then 40v; anything near or more than > that, confirms a leaky PNP or NPN. Be aware that if the NPN is leaky, it > can cause a good PNP to appear leaky, because your driver is basically a > 2-stage amplifier. > > Based on the scope pictures so far, I'm not convinced it's leakage. But we > need to know if we can rule it out. > The last set of scope photos show good turn-on, turn-off, blanking, and > control signal behavior. So I think that can be ruled out. > > There's definitely a clue with the 'ugly' shaped signals; I just havn't > figured it out yet. > > Can I assume your probes are properly compensated ? The leading-edge > 'spike' at the anode when it turns on is hopefully the effect of the tube > ionizing. But on the falling-edge I noticed some undershoot which goes > significantly below 0 volts. That could be a clue. > I think that NPN transistors are not leaking at all, at least not significantly. PNP transistors base signal looks really clean, and also if the root of the problem would be leakage, then the problem would be visible during blanking period. For sanity check I'll try to make a differential reading of a PNP base and HV rail to check if there is a significant difference between those two or not during nominal off time. That again narrows my mind to MMBTA92 only. I have some of these purchased from Aliexpress, I've gotta use these instead and observe if I get same result. I'll check the voltage at the anode with the tube disconnected. I'll have to be careful, the sockets are holding the tube really tight and I bet the glass is getting stressed during dismounting. The probes were recently compensated, however I'll check them again just to be sure. I also see the strange undershoot. It might be just some stray/probe capacitance discharging. -- 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/60f4b3b0-351f-4e0c-ac98-c74fb16dcdb0%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
