> >> - Bargain-price/cheapie/fallout zeners diodes are basically units that
>
> >> fail to pass the manufacturer's final test. I was given a box of them
> >> which was marked "semiconductor scrap". Some were usuable. Some were
> >> not. None were first class.
> >
> > <snip>
> >
> >> quality semiconductors.
> >>
> > <snip>
> >
> > ::I wonder: What is the difference in "quality" between fallout and
> >first-class, in Zeners?
>
> A mixed bag.
>
> >Having fabricated a lot of these (starting with
> >undoped silicon), the "fallout" in manufacturing is usually -- oops!
> missed
> >the target avalanche voltage! -- or -- oops! failed to meet another
> >parameter such as leakage current below avalanche, or dynamic impedance
> >(slope of Vz/Iz).
>
> Inability to maintain constant V with <> I is the sticky wicket.
>
::Well, dynamic impedance, which is the parameter of which you speak
(write), is a function of only three variables: Avalanche voltage; junction
construction; junction cross-section (die area). If one desires low Zz
(dynamic impedance), it's easy to find in very large-area devices, such as
100W stud devices. Placing a bunch of low voltage avalanche devices in
series increases Zz by a factor of how many diodes are placed in series. (I
call these avalanche devices instead of Zeners, because, technically, all
"zener" devices having an avalanche voltage above about 5.6V are not really
Zeners; their coefficient of breakdown voltage is proper for an avalanche
diode, but reversed from that of a Zener device.)
-WB2WIK/6
> cheers, Steve
>
> >...
>
> - R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
> www.vcnet.com/measures.
> end
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