[Amps] HV Diodes

[Steven Katz]

Actually, the SCH5000s found their way into the old ETO/Alpha amps when Ehrhorn was in Florida and we had a good Semtech sales engineer there.  Dick had previous experience working for NASA and ECI and other places using hi-rel parts and was comfortable with them.



Semtech HV rectifier assemblies were also widely used in Henry amps, right after they got rid of 3B28s and stuff.  That's because we had a good Semtech sales engineer there also, who was Mel WB6FDR (now W6FDR).  Same assemblies were also widely used in Harris/RF high power transmitters and amplifiers, because we had a good Semtech sales engineer there as well, WB2WIK.  :)



But they were "mostly" used in defense/aerospace programs where the same design assemblies would be 100% X-rayed, serialized, and burned in for 168 hours at high temperature reverse bias (usually 10% above rated PRV and at 100 degrees C), with "life test" samples running in parallel at full power for 1000 hours and data collected.  If anything failed during these tests, the whole batch would be rejected or subject to 100% re-screening.



Since they were designed to withstand all that, the "commercial" versions are pretty good, as they used the same parts and the same designs.



Circular dice reduce voltage gradient stresses at the edges of the die (no corners for them to build up).  Yes, it wastes some silicon.  They're not "sawed" they're ultrasonically cut and have very smooth edges with no corners - another thing that added to reliability under reverse stress condx.



73



WB2WIK





Steve,



your account of the SCH-5000 is really interesting! So these were very high quality diodes for special high-rel applications. Using circular dies must be a pretty rare thing, I guess, because of the additinal etching and the lower amount of parts per wafer.



How did those high cost parts find their way into ham equipment? I mean, a power rectifier in an amp's power supply really doesn't need to have such ultra low reverse current specs! As long as the better diodes in a string can handle the leakage of the worst ones in avalanche mode, without failing, that should be good enough!



Could it be that at some point these quality diode modules became available as surplus at low cost, and then the amplifier manufacturer grabbed them?



Just guessing again. Darn. Carl told me to stop guessing! ;-)



Manfred







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