The HV5622 has open drain outputs, so the cathodes will be left to gradually float to whatever value they feel like. They probably won't do this fast enough to prevent ghosting and you don't really want them to float in a multiplexed clock anyway. I would suggest a push-pull chip for the cathodes, like the HV9808.
On Thursday, May 20, 2021 at 1:06:54 AM UTC-4 gregebert wrote: > For my current clock project, I have a 9-segment / 13-character display > that must be multiplexed, so I use a 4:16 decoder to drive PMOS > anode-transistors on the high-side. The 4 bits into the DeMUX are piped > thru digital isolators (SI8710), and driven from the FPGA. I use an > isolated DCDC converter to provide a negative 12V supply relative to the > anode supply (about 200V, because it's unregulated). > > The low-side for the cathodes are just NPN current-limiters, also driven > by the FPGA. > > > [image: ScreenHunter_32 May. 19 22.00.jpg] > On Wednesday, May 19, 2021 at 9:21:49 PM UTC-7 Richard Scales wrote: > >> I am trying to learn about multiplexed displays (I thought it was about >> time I had a go at this) and I believe that I understand the basics - in >> as much as it requires the switching of the required anode as well as the >> required cathode (all of which are wired in parallel). >> >> I understand that I can use something as simple as a single transistor >> for the cathode (low side) and a couple of transistors for the anode (high >> side). >> >> Again, for the low side driver I could use any of the 'standard' shift >> register type drivers that we use in clocks such as an HV5622 (I appreciate >> that's way too many bits and I'm sure that there will be a smaller >> equivalent part available. >> >> Specifically - is there such a part that I could use for the high side, >> ie switching the HV to the relevant anode? >> >> I know that I could use a simple shift register (74595 for example) plus >> the transistors for a high side switch, I just wonder if there is a part >> which does all that in one package? >> >> All pointers gleefully received. >> >> - Richard >> >> >> -- 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 view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/b9b1aeb9-989b-453e-854d-0bfc8fe80a9en%40googlegroups.com.
