An Engineer's Logical Disconnect

This passed by me on an email list and frankly I’m not shocked to see this particular logical disconnect. (Emphasis mine)

I once had a vacation canceled because all 150 of the high tech switching power supplies that had been 100% qualified at 50C for 24 hours were shipped to the integrator where all 150 failed spectacularly near simultaneously after 72 hours at 40C.

The fault was an opto isolator in the current feedback path. It was a an expensive full mil spec part specified for 5000V RMS AC, but carried no DC rating. At 500VDC …

This was a supply design that had been rigorously reviewed and subjected to extreme testing…

That is NOT a rigorous review when you don’t pay attention to the specifications for a part in your design! Sadly I’ve encountered these kinds of problems far too many times in the past 25 years. It seems to be a common problem that engineers will say they’ve made a careful review of a design and when I review the design I find they either failed to read or ignored a components specification. I’ve seen this exact mistake on switch applications where AC vs. DC operational differences are missed or ignored. IME, a more commonly ignored specification is component operating temperature range, it seems many people think that all electric components have no lower limit on operating temperature, RTFM!

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