Greg, Would you mind listing the current limiting parts you use for both the PMOS high side and the NPN low side drivers? Thanks; -Bill-
On Tuesday, May 25, 2021 at 3:54:18 PM UTC-7 gregebert wrote: > I'm attempting my first multiplexed nixie project, in this case a > 13-character / 9-segment display. Direct-drive is always my preference, but > that is not an option due to the way the display is pinned-out. > > I'm using an FPGA to control the multiplexing, so I've put a lot of > software-controllable registers to set the time when anodes and cathodes > are turned on and off to prevent ghosting. For my display, the blanking > time is 20-100usec per the datasheet; I believe this is the time required > to dissipate the charge from the ionized gas. I measured less than 10pF of > capacitance between the various terminals, but I'm certain this is an > underestimate of the actual charge that an ionized segment holds, so you > really cant calculate the correct value of the bias resistor based on the > time-constant from the blanking time and the measurable capacitance. > > The anode-driver is a PMOS current-limiter that can be switched on or off, > and the anode will be biased around +100V thru a 5meg resistor (two 10-meg > resistors dividing the anode supply in-half). Cathodes are driven by NPN > pulldowns that are current-limiting (3mA per datasheet). If I'm unable to > eliminate ghosting by changing timer values, I will reduce the anode bias > resistors. > > Unfortunately I have 3 projects going right now (too many!!), so I wont > have any progress update on this for awhile. > > On Monday, May 24, 2021 at 10:25:44 PM UTC-7 Richard Scales wrote: > >> I think I am getting a little closer to understanding this all a little >> bit more. I have almost grasped the concept of clamping the cathodes at an >> intermediate voltage to aid switching them on and off in a timely manner in >> an effort to minimise ghosting. >> >> Now it's all down to driver choice and chip count. >> >> How about HV5812's? i have seen these used in multiplexing circuits - >> especially those where a group of say 6 nixies are split into two groups >> then the 20 bits from the driver are split into two groups of 10 bits, >> each group for one set of three nixies. that works just fine for nixies, >> not so good for a 16 digit device with cathodes common to all! >> >> Regardless, it would be slightly more efficient than using a 32 bit >> device though ultimately an 8 bit device would suffice. Using the HV5812 I >> can see that I can just connect Vpp to 80V, job done. If I wanted to use >> HV513 (on the grounds that I only need 8 bits) would I then just clamp each >> cathode to 80V via a suitable resistor? >> >> I guess I could simply not worry about it and waste the bits, I'm only >> ever going to do this once or twice and one of my design goals is to make >> this thing as small as possible. >> >> For the high side i definitely need to switch 16 anodes so I need to >> employ a push/pull device - HV5523 will do that or I could perhaps use a >> couple of HV513's - again, the easiest thing to do would be to use a single >> HV5523 and waste half of the bits. >> >> In an effort to home in on a solution - a single HV5523 for the 16 anodes >> and a single HV5812 for the cathodes (clamped to 80V) - have I missed >> anything crucial here? >> >> I just feel that I should get a handle on this multiplexing thing. I now >> have a couple of different multi digit panaplex displays coming so I need >> to come up with a plan. >> >> I have some ZM1500 (12 digits) on hand and some IGP-17 (16 digits) on >> their way. >> >> ... and I've not even started to think about the timing of all the >> various switching operations yet! >> >> Thank you all for helping me with my education >> >> - Richard >> >> On Friday, 21 May 2021 at 19:13:35 UTC+1 nixiebunny wrote: >> >>> Richard, >>> A single push-pull HV driver chip will not be able to drive a >>> multiplexed display. >>> >>> The reason is that it only connects each tube element to either 0V or >>> 180V. It is not capable of leaving an element disconnected. >>> >>> >>> On Thu, May 20, 2021, 8:45 PM Richard Scales <ric...@scalesweb.co.uk> >>> wrote: >>> >>>> Sorry, I mean using the same type of device to control the anodes AND >>>> the cathodes but but the actual same piece. >>>> So, using an HV5523 (or perhaps multiple HV513, multiple because there >>>> are probably 8 cathodes (seven segment panaplex displays) and 16 Anodes >>>> (16 >>>> digits)) could be a way forward then. >>>> Please could you let me know more about the need to clamp the cathodes >>>> to a certain voltage? (Exposing my real lack of understanding here!) >>>> - 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/e182dafe-0772-46df-b09a-77b52cddc1fdn%40googlegroups.com.
