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Apologies:
? Perhaps the? practical? aspects of my thread were not well stated.
?
(? ... after all,??? who would want to lose the Cal Constants of their fine instrument,
?????? due to a prematurely dead Sram battery, .... caused by exponentially failing? Schottky diodes ?
?
a)
? ** ? Has anyone replaced their Schottky's **?
?????? in Sram (non Dallas) battery backed-up instruments,
?
to prevent? Cal Data? loss ?
?
&
?
b)
? ** ? Has anyone found any other Service Bulletins for other instruments
describing Schottky >> Si? replacement suggestion **? for? Sram battery improvement? ?
?
?? --? if so, ? I'd like to see the .pdf's.
?
?
That some Schottky's fail over time;? ( ion migration, barrier puncture, etc. )? is not in question.
?? This has been documented in semiconductor failure research papers.?
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For this particular application, replacement with Si diodes might very well be good insurance in the Sram Battery back-up circuit:
?
Most of the Srams themselves,? of the day, were Cmos +5V Vcc types( working range of 5V to 2V ), so a back-up battery type having 3.0V Li+ ( i.e., BR-2/3a? , common at that time) was commonly used with Schottky's chosen to have a lower voltage drop,? within a Mains Power Down/Up/Down (On/Off) switch-over circuit, from Batt > PS > Batt,? ... to preserve the Sram Cal Constants.
?
-- A 3.0V Battery & Schottky replacement,? today, to preserve the Sram Cal Constants, with? a 3.6V Li+ Tadiran or SAFT LSH-14 cell, using the suggested replacement Si diodes might be warranted,
in light of the now known Schottky failures over time.
?
( ' Having a thought, Barbossa ' ... arrrgh ):
New 3.6V Battery voltage up by ~ the amount of the ( more stable ) Si diode voltage drop, down.
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As for 30+ year old instruments, having Sram battery backed-up Cal Constants:
-- Many of these invaluable, precious instruments continue to be? used, as Standards, by Semiconductor Fab test labs, military, university research, and national metrology labs worldwide.
Some are still manufactured and sold,?? such as the GR Digibridge? LCR meters ( IET 1689, 1693, etc. ).
?
??? 10k$ today;?? &? " the US Army's Impedance Bridge "
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Of course, we now have the Quantum Hall standards, ... but not everyone can afford that one (& good luck running it in your basement without costly LHe/LN2 on tap ! ) , but the national metrology labs still use and calibrate the older 1693, & other older great Hp equipment. And we still receive such instruments to be calibrated by clients.
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Thank you elder Hp Engineers, for the Schottky Service Notes and insight, certainly helps !
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On Sun, Sep 1, 2024 at 11:58 AM, gren wrote:
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