On Sun, Jan 22, 2012 at 3:18 PM, Robert LaJeunesse <rlajeune...@sbcglobal.net> wrote: > Specifying the digit scan transistor is a bit tricky, and often power > dissipation is just not a concern. Why? Consider the duty cycle. A transistor > switching one amp (a LOT for 7+1 segments) with a 0.6V saturation dissipates > 600mW, but only when on. Given a 1/8 duty cycle that's 75mW average. Any > stinkin > TO-92 will handle that power all day long! Only an ultra-conservative design > would use an exposed tab transistor, as expected for HP!
Ultra-conservative and "overkill" but two of the nine failed. OK it is 30 years old (made is '83, I think) These were in air. The tabs were not screwed to anything. I think looking at how this display works it was likely used for many different instruments, not just the hp5328. They must have sold many thousands of these > Chris Albertson Redondo Beach, California _______________________________________________ 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.