PMOS is DMP45H150DHE ( https://www.diodes.com/assets/Datasheets/DMP45H150DHE.pdf ) , with 350 ohm source resistor NPN is a PMBTA42DS (dual NPN) with a 1.3K emitter resistor. Base is driven from a 3.3V FPGA. ( https://assets.nexperia.com/documents/data-sheet/PMBTA42DS.pdf )
On Tuesday, May 25, 2021 at 4:19:35 PM UTC-7 Bill Stanley wrote: > 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 <[email protected]> >>>> 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 [email protected]. 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