On Mon, 23 Jan 2012 17:27:32 -0500, "Charles P. Steinmetz" <charles_steinm...@lavabit.com> wrote:
>Stan wrote: > >>The 5328A manual I have shows a 3.5 V supply (looks like it is used just >>for the display). But with a bit lower Vce sat drops, I'd guess you >>get around >>1 V across the 10 ohm segment resistors. Or only about 900 mA when all >>9 segments are on (but at a low duty cycle). Did HP also use a 5 V version >>of the driver in some 5328A counters? > >Interesting. I have 3 different sets of schematics for the >5328A. The most legible of these (thus the one I consult first) >shows a 5 V supply for the display. The other two show 3.5 V, as >yours does. I cannot recall ever measuring the display supply >voltage in a 5328. > >Even with 900 mA per digit, I'd want a transistor with >/=2 A maximum >collector current for the digit drivers -- so I still think the >ZTX949 may be the best readily-available choice. I am surprised the LED current is so high. I always found diminishing returns above 20 mA but some LED types are better than others for multiplexed applications where the peak to average current is high. 8 x 20 mA also conveniently stays below the bond wire limit if you drive 7 segments plus the decimal point directly with a single IC without multiplexing. I would use a 2 amp or greater transistor just to keep the gain high although I know those Zetex transistors much better about that. I think Fairchild has a similar line of high beta, high current, low dissipation transistors now as well. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
