All good points. "The 2 diodes on the HV series parts (CMOS) are actually parasitic devices that are part of how the IC is manufactured."
That's part of the reason I give the HV5812 the hairy eyeball. At least in the ULN the diode is there as part of the design, specifically for inductive loads. I *know* it's going to be OK, but... I'm probably retrofitting a justification to a decision I made for other reasons: I'm a cheapskate and I can get the ULNs from a dozen competing suppliers. :D On Saturday, 8 March 2025 at 09:56:05 UTC+1 gregebert wrote: > All good, though the ULN parts are bipolar devices, so there should not be > any fear of them getting damaged by over voltage, unless it's an extreme > over voltage that punctures the field oxide (way, WAY thicker than gate > oxide in MOS devices). > > The 2 diodes on the HV series parts (CMOS) are actually parasitic devices > that are part of how the IC is manufactured. They provide ESD protection as > long as there is some sort of path between VPP and GND, and they will > protect you from inductive loads, though I don't expect a lot of Ldi/dt on > those parts because they are rather low current compared to the ULN devices. > > I think a zener clamp on VPP is a good idea because it will rapidly > bleed-off any excess voltage better than resistors. However, the zener wont > bleed-off voltage to zero so I usually put a 1-10Meg resistor across them. > On my clocks I put bleeder resistors from every power supply to chassis GND > to protect from any potential ESD and to ensure every supply gets fully > discharged when powered-off, and stays fully discharged. I've only had 1 > Raspberry Pi fail, presumably from ESD, because it had an unknown history > from the person who gave me several of them. > > On Saturday, March 8, 2025 at 3:26:00 PM UTC+7 Ian Sparkes wrote: > >> I started using ULN series devices during the supply chain problems after >> Covid and won't be going back. Many "specialist" parts were not in stock >> and so I decided to use "jelly bean" parts with multiple suppliers. A >> driver circuit with ULN2003 or ULN2008 with appropriate clamping works >> well. I clamp to 68V, and while this is above the specification for the ULN >> device, I have still to see a single failure after many hundred units sold. >> >> Many people think that because you have 170V or whatever across the tube >> that the driver has to stand this. This is not right. The tube digit has >> two modes: off or on. When the digit is off, there is practically no >> potential across driver because there is no current flowing. When it is on, >> you're pulling the cathode to ground and it has practically no potential >> across the driver. >> >> The reason that the above statement is not quite true and the reason >> therefore for the clamp is to sink parasitic currents between a lit digit >> and the unlit ones. If you don't do this, you can get way out of spec >> voltages at the cathodes and this causes the output stage on the driver to >> break down and let the tiny currents through. It rarely breaks the device, >> but the display is "foggy". >> >> The principle for the HV5812 is the same. In this case you have to take >> the VPP pin to some voltage that will not cause the digit to fire, but will >> also drop the parasitic current via the body diode of the top MOSFET in the >> output stage to VPP. The red is the path when the digit is on, the green is >> the path for the parasitic current to VPP when the digit is off. >> >> [image: Screenshot 2025-03-08 at 09.17.21.png] >> >> I've seen people just using a potential divider for the derivation of >> VPP, but I think I would prefer a Zener clamp. >> >> Having said all that, if you want a direct drive and don't want to go >> full design nerd, the HV5622 and HV5530 drivers are dead easy to use and >> give good results with little effort. >> On Monday, 3 March 2025 at 21:46:45 UTC+1 gregebert wrote: >> >>> Similar here, except I use the HV5530 which is rated for 300V. I >>> strongly discourage using zener diodes, or the nixie-tube itself, to >>> drop-down the voltage to CMOS parts, because even the tiniest amount of >>> leakage thru the diode/nixie will cause the voltage drop to be less than >>> expected, and overstress the CMOS device. You could use an >>> appropriately-sized bleeder resistor to ground, but it's still not >>> rock-solid. Another approach is to use a zener as a clamp at each output >>> but that is wasteful because it requires 1 zener per pin. >>> >>> On the other hand, if you are using bipolar parts, such as NPN >>> transistors or 7400-series TTL parts, exceeding the voltage is OK as long >>> as the current is limited to a few uA or less. Bipolar devices do not have >>> oxide-insulated structures like CMOS, so they are not inherently destroyed >>> by over-voltage. >>> >>> On Monday, March 3, 2025 at 11:39:00 AM UTC-8 newxito wrote: >>> >>>> I use the HV5622, which goes up to 220 V, I think there is also a PLCC >>>> version. The disadvantages are the price and that it should be operated >>>> with 12V according to spec. However, I never had any problems using the >>>> chip with 5V. >>>> JBro63 schrieb am Montag, 3. März 2025 um 19:02:56 UTC+1: >>>> >>>>> Hi all, >>>>> >>>>> Group noob here, about to start build on a few different types of >>>>> display using Nixie tubes and ESP32. >>>>> >>>>> Planning to use K155ID1 initially (as I have a bunch) with some IN-12 >>>>> and IN14 tubes but want to also try HV driver such as the 5812 or 5530 so >>>>> would welcome any comment on which is the best one to go for or an >>>>> alternative. I don't intend to multiplex. Any driver would need to be DIP >>>>> or PLCC. >>>>> >>>>> Have spent many hours looking at the schematics and designs of others, >>>>> I'm grasping the basics but one frustration and evident gap in my >>>>> knowledge >>>>> is how to pick / calculate the correct component and its size or rating >>>>> for >>>>> anything other than the most basic circuit. >>>>> >>>>> For example, with a 180v supply, calculating the anode resistor for a >>>>> tube based on the datasheet is straight forward enough as the maintaining >>>>> voltage and current are known. >>>>> >>>>> When looking at something like the HV5812, many seem to use a 60 or >>>>> 70V zener diode with a resistor to keep below the max for the chip but >>>>> how >>>>> do you determine the current needed for the driver, diode and load to be >>>>> able to calculate the current limiting resistor? The diode datasheet is >>>>> simple enough but I'm lost with the sheet for the HV5812. >>>>> >>>>> Thanks. >>>>> >>>>> -- 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 view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/4cd82f32-704d-4777-817e-d09eb2134589n%40googlegroups.com.
