> >
> >
> >
> >
> >
> >
>
> >> >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.
>
> If the delta V for one diode ia 2%, the delta V for 100 of them in series
> is 2% even though the regulated V is 100x higher.
::Absolutely true, although Zz is expressed in Ohms, not percentage;
however, if you do the math, it comes out the same. The problem is that Zz,
and thus regulation, is not held well by small-area junctions. The Zz of a
small device might be 10-20-30 Ohms, so dynamic regulation (in V) is "I"
(current) x Zz. If you place 10 devices in series, each having a Zz of 10
Ohms, the resultant Zz is 100 Ohms. V = I * 100. However a large die
device having a Zz of 1 Ohm, when placed in a series string of ten, has a
resultant Zz of 10 Ohms. V = I * 10. Obviously, ten times better dynamic
regulation. That was my only point.
-WB2WIK/6
> >(Icall these avalanche devices instead of Zeners, because, technically,
> all
> >"zener" devices having an avalanche voltage above about 5.6V are not
> really
> >Zeners;
>
> Good point, Steve.
>
> > 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
> >
> >--
> >FAQ on WWW: http://www.contesting.com/FAQ/amps
> >Submissions: amps@contesting.com
> >Administrative requests: amps-REQUEST@contesting.com
> >Problems: owner-amps@contesting.com
> >
> >
>
>
> - R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
> www.vcnet.com/measures.
> end
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