[AMPS] Shunt regulated high voltage psu

[rich]

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>> >> >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.
>
Agreed

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
end


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