[time-nuts] HP5328A LEDS driver transistor
Chris Albertson
albertson.chris at gmail.com
Mon Jan 23 04:51:34 UTC 2012
On Sun, Jan 22, 2012 at 3:18 PM, Robert LaJeunesse
<rlajeunesse at 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
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