This is my first post here but I've been involved in electronic circuit design for many decades. As part of a current design effort I take an unconditioned AC voltage, put it through a bridge and large capacitor to get maybe 9 volts, then I pass that through a linear regulator to get 5 volts, then I send that to a (typically Chinese-made) 1 watt isolated dual +/-12 volt DC-DC power converter module. (Please note I'm NOT looking for circuit design help so I'm not posting schematics or anything else that isn't relevant.) The trouble is on the (typically) second or third power cycle the device outputs will be zero and the module will be burned out, EVEN IF I HAVEN'T EVEN HOOKED UP THE OUTPUTS YET, the linear regulator (typically LD1117) is never harmed, nor is a second module across the SAME input that's generating isolated +5 for another purpose! The vendors I've identified for this type of product are aimtec, CUI, Mornsun, gaptec, Mean Well, XP and Cincon, so far I've blown out two from each of the first two vendors (I don't even have parts from all these brands, still waiting on my distributor for delivery for some of them). A representative part # (aimtec) would be AM1DS-0512DJZ. So far when I talk to any of their "support people" all I get is "what is your company name and website?" as if big customers are the only ones "entitled to" application and reliability support. It seems to me all these parts basically come out of some windowless factory in China and NONE of these vendors know anything about the product design or application! The only "clue" I have is SOME vendors say the modules OUGHT to be "protected" from "undervoltage conditions" but there isn't an actual spec at which they admit the module would self-destruct! Is there some "minimum level of product" below which it just isn't advisable nowadays to expect any level of reliability or support AT ALL? (These aren't for DOD application so I don't have an infinite budget, it's a consumer product with an extended warranty so I can't afford gold-plated stuff but it DOES have to be generally reliable.) When did the market change so that power supply modules can be so goll-darned unreliable but somehow they still meet the requirements of the market? Has anyone had the same level of frustration with this type of product, and how did you resolve it?
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