Chris wrote:
HP does drive all the segments at once. They multiplex one digit at a time. So worst case is the transistor has to drive all 7 segments and a decimal point.
Six or seven of them (depending on the model variation) also drive an annunciator LED, for a total of 9 "segments" on those digit drivers.
I checked after running for a while and these transistors don't get even close to warm. I think they were selected for peak current, not average.
I think you may mean they were selected for current rating, not power rating. In the 5328A digit driver circuit, the required current rating is the more demanding spec because it is harder to meet with a small transistor than the required power rating.
Some transistors are rated for greater peak current than average current, some are not -- it depends on the particular current breakdown mechanism of each transistor, and what kinds of applications it was designed for. The MPSU51 is not rated for peak current in excess of average current, the ZTX949 is. But this should not be a factor in the 5328 digit driver circuit for either the MPSU51 or the ZTX949, assuming a 3.5 V supply, because both are rated >= 2 A continuous and the load is < 1 A maximum -- even if this load were continuous, both transistors should survive (if your 5328 has a 5 V display power supply, the MPSU51's 2 A rating would be cutting it close).
Best regards, Charles _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
