[sebhc] The 8-bit Runt of the Litter: ET-3400
leeahart at earthlink.net
Wed Sep 8 02:40:58 CDT 2004
Dwight K. Elvey wrote:
> I'd often wondered why myself. A 1N4148 is spec by spec
> identical with a 1N914. I looked into this and found that
> the difference was in the process used to create the diode.
The 1N914 was a gold-doped "very fast" switching diode. But optimizing
switching speed makes its forward voltage drop vs. current higher; their
forward voltage drop rises over 100mv per decade current increase.
Time passed, and semiconductor technology improved. The 1N4148 was an
improved, more expensive version of the 1N914, with more standard doping
and thus less forward voltage drop.
More time passed. As 1N4148 sales volume became higher, its price
dropped. The 1N914 sales dropped, until its price was higher than the
better 1N4148. At this point, manufacturers just dropped production of
the "real" 1N914 and used the same 1N4148 die in both parts. So today,
both parts are really the same.
This behaviour has continued. Huge numbers of today's diodes and
transistors are in fact all the same few chip; just marked, packaged,
and sorted differently.
Once in a while, you will run across a high-performance circuit that
really *does* care what you use in it. But design engineers know that
their Purchasing dept. will buy whatever is cheap from whatever
manufacturer promises fast delivery. So, they don't design their circuit
to depend on parts that truly meet their specs.
"Never doubt that the work of a small group of thoughtful, committed
citizens can change the world. Indeed, it's the only thing that ever
has!" -- Margaret Mead
Lee A. Hart 814 8th Ave N Sartell MN 56377 leeahart_at_earthlink.net
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