Hi The HC series of parts is way past being state of the art for this sort of thing. Even the AC series is getting a bit old. There are a number of high speed / high current parts out there the NC7SZ125 is one of many many devices out there.
Bob > On Oct 5, 2021, at 7:04 PM, ed breya <[email protected]> wrote: > > My plan has been to go with it being a 50 ohm source. My go to driver setup > for these sorts of things is a 74HC/AC 500 series octal bus device, so you > get all the ins and outs across each row of pins - easy to parallel. > > For now, it's looking like a 74HCT541, with the outputs ballasted with series > 220 R, contained in a SIP R package. Depending on how many outs will be used, > this gets it into the 30 ohm ballpark, not including the device output > resistances. The rest of the 50 ohms is a PTC, about 10 ohms, plus a tweak > resistance selected to set it about right overall. So, it will deliver about > +2.5 V into 50 ohms, or 100 mA into a short. Any external fault input applied > will get clamped behind the PTC and tweak R, and the PTC will limit the > current. The HC541 will be in a socket too - just in case - and allow for > experimenting with AC541. Also, because of the possible high output demand, > this section will run on a shunt regulator. like I did long ago for the > digital clock LED supply to eliminate pattern dependent loading. The same > goes for the circulation fan ripple current - I just finished that part > yesterday. > > Presuming this "pseudo-ECL" is just PECL, I'll be using a comparator to shift > it to TTL/CMOS. I have some nice high speed ones like LT1016, but > unfortunately it won't quite work out, PS-wise, without more complexity. > After looking around, I determined that the good old LM311 will do the job > directly, but maybe ten times slower, unfortunately. I'll probably end up > using an HCT541, just to get the threshold down a bit more for better > matching with the LM311. I'm really cramped for board space, so simple and > compact is the goal, even if it could be much better. I'm still thinking > about a possible discrete circuit, but it's hard to beat just one comparator > IC for space. > > > BTW, this unit does have the RS-232 mod, which I did many years ago. I think > the last time I had it hooked to a PC and talked to it was around 2008. > Sometime around then is when I decided to rebuild it into the 5065A carcass > (I think I've mentioned this before). The original Z3801A layout is hardly > recognizable, since I had to make extreme mechanical changes to cram it in > there. I have to plan carefully which things I do together, to minimize the > number of times I have to take things apart for access. > > So anyway, this 1 PPS thing is up now, next will be the clock, then > communication, then the battery system (two 12 V 12 A-hr SLAs built in), then > the control panel, clock setting system, instrumentation, thermal control, > etc - it goes on and on. Every so often, I get a burst of enthusiasm and get > a bunch of things done on it - but certainly not all, so it will wait until > next time. At least this time, I think I'll be able to shove all the loose > ends inside, and put the covers on. > > Ed > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
