@greg I'd like to ask something related to the B7971 since I'm designing a PCB for the clock at the moment. I have implemented the controlled current sinks for each cathode and will fine tune the current for each segment (already discussed in the HV control chips thread with the schematic). I'm wondering if you implement both the cathode sink drivers and the anode driver you proposed here:
1) If sum of all lit cathodes currents exceeds the maximum value in the datasheet (the current set on the PMOS controlled source) what will happen to the currents of the individual segments, will they proportionally go down for each activated cathode? If so, will this cause the tube to reduce the glow? 2) If the sum of all lit cathodes is less than the maximum defined in the datasheet, it's supposed to stay that way because the PMOS source only limits the upper maximum current but does not enforce it constantly to flow trough the tube when it's activated? 3) How important do you think the maximum current per tube control is? Before deciding to go with the sink controller for each cathode, I browsed for other solutions to drive the B7971 and most of them use resistors, but these resistors have to limit the current to rather low values, are these enough to light the tube properly? For example, http://tayloredge.com/storefront/1386_B7971SmartSocket/1386A.pdf Segment 11 in the datasheet is defined for a max current of 5.5mA, but the above schematic would produce (170V - 140V) / 24 kOhm = 1.25mA. This seems rather low? Dana nedjelja, 26. ožujka 2017. u 09:01:56 UTC+2, korisnik gregebert napisao je: > > Some other things I forgot to mention... > > 1. Generally, you would use a current-regulator on the anode side for > non-segmented tubes (0-9), where all cathodes use the same current. > > 2. Segmented displays (b7971) have different currents for various > segments, so you will need cathode-side current-regulation. I chose to > include an anode-side current-limiter as well because the Burroughs > datasheet specifies a max total current. This max current is about half the > sum of all the spec'd individual segment currents. > > 3. If you use MOS devices, be very careful not to exceed the max-voltage > specs. Doing so will damage the device (impaired reliability, or outright > destruction). I've done some research on MOS device-failures and they often > fail-shorted, which is disastrous. Fortunately, those kinds of failures are > mostly caused by overstress (voltage or temp). > -- 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 neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/bea2bf0a-852e-4d8a-a6f1-57e7ffe79835%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
