I'm happy to read that.
I'm curious what would happen in a circuit with both anode 22mA limiter and cathode limiters after the anode limiter kicks in - will the current of each lit cathode get lowered by same percentage or will it equalize to same value on each cathode and then lower further with the same value? Anode limiter could possibly lead to uneven illumination of segments, if first option was the real one. Unfortunately, B7971s are totally out of my league and I can't test it myself. W dniu środa, 10 maja 2017 09:39:03 UTC+2 użytkownik Luka C napisał: > > I'm glad you've done the test with BSS139 and it turned out to work fine. > I've used the same transistor for the cathode current control on my B7971 > clock, completed routing the PCB and currently sparing some money to send > it to the fab house :) > > Dana utorak, 18. travnja 2017. u 11:08:58 UTC+2, korisnik Tomasz Kowalczyk > napisao je: >> >> I've ran some tests with BSS139 + a potentiometer as a variable resistor. >> Conclusions: >> - this design offers cheap and stable current limiting >> - it varies with voltage dropped over the circuit, so it should be >> tunable - the difference is about 14% change between 5V dropped and 105V >> dropped across it (4,37mA vs 4,91mA). >> - it is thermally stable - at 100V dropped and 4,93mA cold current I am >> breaking the allowed power dissipation (allowed 0,36W, here - 0,5W), it >> heats up to a bit over 50°C (many probe cables connected close to the >> transistor act like a radiator), the current has changed by 40µA >> - while testing it I found out that striking voltage of tubes is a max >> value - I've tested one Z567M and one LC-631, they both strike with >> voltages lower than their normal maintaing voltage! While powered correctly >> they sit at 140V across the tube, and I was able to lower power supply >> voltage to 135V, disconnect tube, connect it again and it worked. I >> suspected that due to large resistors and a cap in the feedback I have high >> pulses over 170V in my supply, but it is not true - at 135V the spikes >> measured with an oscilloscope were less than 5V. Of course, with voltage >> lower than 140V + minimum drop over BSS39 and resistor, the current was >> lowered. >> - due to that it is possible to create a clock wasting very low power on >> anode limiting - classic operation uses 170V, 180V or 200V supply + >> resistor, which wastes quite a lot of power on those resistor. here we can >> tune the power supply just above striking voltages of all tubes and be sure >> that we don't have to recalculate the resistors. This will have a very >> positive effect in clocks which run on batteries or USB supplies - with >> both lower voltage required and lower power consumption. >> - after tuning to desired current it is very stable - drift is max 20µA >> I wonder if this low striking voltage is common among different tubes or >> does the striking voltage change with temperature. >> >> In my opinion the only drawback of this design is that it is changing the >> current with voltage drop across the limiter. This change in normal >> operation shouldn't be noticable, because normally power supply doesn't >> change much - maybe 10V under bad circumstances. With such voltage change >> the current will be pretty much the same, but a resistor calculated once >> isn't universal for every design. >> Everything else (simplicity, price) says that this is it, I'll be using >> this instead of resistors. >> >> I'm attaching photos of setup - left multimeter measures voltage across >> the tube, middle measured power supply voltage, and the right one measures >> current (in mA). Voltage across limiter is of course the difference between >> middle and left. >> > -- 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/8b4f3f02-97bc-419c-b6f8-59a07bf76641%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
