DS8884AN substitute? - Page 1
Forum section: electronics / repair

author: TheMG
author_rank: Frequent Contributor
timestamp: August 15, 2020, 01:53:14 am
content: Dug up a a rather peculiar old clock that uses neon gas plasma 7-segment displays. Works except for one digit, which has a missing driver IC. I guess someone was going to repair it, found the problem was the driver IC, removed it from the PCB but was unable to source a replacement and it ended up sitting in a pile of junk for X number of years until I got my hands on it.DS8884AN DatasheetUnfortunately, this IC is long obsolete and has fallen into the near-unobtainable category. Best I could come up with is a few Chinese eBay sellers at the absurd price of $33 or more plus shipping cost, EACH!!! Not worth it, especially since there's really no way of knowing if these are even real.The chances of finding a drop-in replacement, I assume, are going to be next to nothing, as there would be no need for such an IC in any kind of modern electronics.Best I can figure, is a 74LS47 BCD-to-7-segment decoder with either individual transistors or some kind of high voltage driver IC. The trick is, the DS8884AN has built-in current limiting function. Any high voltage driver chip available these days with such a function suitable for driving a neon display? I suppose I could go real basic and just use resistors, but the PCB (which would have to fit in the space where the original DIP-18 IC used to sit, would get a little crowded with so many discretes.Ideas/suggestions (besides throwing the thing in the bin)?

author: Clear as mud
author_rank: Regular Contributor
timestamp: August 15, 2020, 02:04:30 am
content: My first result when searching was the partfor $23. But I think the web site is probably Chinese like whatever you already found.at the text on their "About Us" page.

author: TheMG
author_rank: Frequent Contributor
timestamp: August 15, 2020, 02:15:53 am
content: Don't forget that's $23 USD converts to $31 CAD.

author: Clear as mud
author_rank: Regular Contributor
timestamp: August 15, 2020, 02:41:19 am
content: Oh well, sorry for being less than useless with my first reply.I thought about how to build something, but it still might be too large. Take your BCD to 7-segment driver and put the output to aULN2803transistor driver, rated for 50 volts, then take the 8 outputs of that and run through an array ofcurrent regulator diodes. Unfortunately, I don't think the current regulator diodes come in an array. From what I saw just now while searching, they only come in DO-7 (regular through-hole diode), MELF, and sometimes SOD-123 packages.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 15, 2020, 05:46:10 am
content: You have :DI270B, DS7880, DS8880This one(s) seems available ??K155ID1 as low as 1$ usd on ebay ??Maxim MAX6922 Digikey ??

author: Clear as mud
author_rank: Regular Contributor
timestamp: August 15, 2020, 10:07:03 pm
content: I just happened to run across another method of limiting current, rather than a current regulating diode, which are mostly obsolete I think.Using 2 depletion-mode N-channel MOSFETs and a resistor as in the picture.

author: TheMG
author_rank: Frequent Contributor
timestamp: August 16, 2020, 06:29:44 pm
content: Interesting, I had no idea there was such a thing as a current regulating diode!I managed to find some DS8889 in the stash. Maybe DS8889+74LS47 combo would do the trick without too much fuss?I would definitely have to get a little creative to squeeze it into the limited space available. Maybe make a little board with the DS8889 (DIP package) on the top and the 74LS47 in SOIC package on the bottom side.

author: james_s
author_rank: Super Contributor
timestamp: August 17, 2020, 12:54:31 am
content: You know the supply voltage, you should be able to use resistors (or a resistor network) to limit the current. I have built numerous clocks around nixie and similar gas discharge displays and I always just used resistors. Actually for the clock built with B-7971 segmented tubes I used a single anode resistor and it works fine, the resistor is sized to not overdrive the display when a '1' is displayed and the brightness change with an '8' displayed is nearly imperceptible.

author: FransW
author_rank: Frequent Contributor
timestamp: August 17, 2020, 09:06:54 am
content: There are quite some equivalent drivers around, such as"DI-8884A High Voltage Cathode Decoder/DriverDirect Replacement for National DM-8884A = DIONICS, INC.Further reading in National Semiconductor AN-84:Driving 7-Segment Gas, Discharge Display Tubes with National Semiconductor Drivers (April 1986).Are you sure the 8884 is the culprit and not the Panaplex (?) display.Philips used these displays and drivers in their frequency counter seriesPM6611, PM6613, PM6614, PM6615, PM6622, PM6624 and PM6625 .The driver were DI, DS & DM8884AN's. How sure are you it is the driver and not the neon displaywhich, to my knowledge, is more common. They succeeded the Nixies initially, some 40-50 years ago.First in calculators.Two of my counters show the display performance differences. I did not check the driver performance by exchanging the drivers.Pic 2 is the faulty and pic 1 the correct display.When needed I can include the application note and the driver specs I have.Regards, Frans

author: TheMG
author_rank: Frequent Contributor
timestamp: August 18, 2020, 02:26:33 am
content: Quote from: FransW on August 17, 2020, 09:06:54 amPretty sure. For one thing, the IC is missing (someone else had removed it), so it will need to be replaced regardless. The clock is also designed using 3 socketed two-digit modules (Babcock SP-352) and I have several spare modules. I interchanged them into one of the fully working positions and they all test good.The DI-8884A doesn't seem any easier to find than the DM-8884A.

author: FransW
author_rank: Frequent Contributor
timestamp: August 18, 2020, 07:49:05 am
content: You might want to have a look at:http://embedded-lab.com/blog/tag/hv-seven-segment-led-driver/or Google: HV-display driversor just replace the display by 7 - 14 segment leds, which seems to be more practiclefor this day & age.That's what I am doing with my PM counters. Buying cheap faulty ones is not that difficult and repairing straight forward.Not needing high voltage drivers simplifies the problem.However, this is not exactly what you are after.Success, FransAttached AN-84 and HV Display Drivers - Dionics-USA Incorporated