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Thread: Load Table and Temp. Ratings

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    Default Load Table and Temp. Ratings

    How the heck do these companies come up with their load table and rated temperature values? I mean, clearly units can be overloaded past those points, so for a typical power supply OEM, how does the decision-making process go when coming to a load table. Are they throwing numbers out of their pants? Same goes for temperature ratings. You see 40C rated units but they clearly handle higher temps even under max load until they shut off from OCP or OPP. I just don't understand where these numbers all come from; I typically ignore them since they don't really mean much of anything other than being simply what they are: ratings. You know, you got those people who analyze the numbers, "you got x watts on y rail" but really it's not even true since they can clearly surpass their rated amperages (except cheap junk, which can't quite meet it).

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    The amperage is a combination of at least two factors.

    One is knowing the absolute limitations (at which the parts break down) of the parts used; from the transformer, via the traces and rectifiers, to the coils and wires.
    The other is having a set limit of acceptable performance. Meaning, if the goal is to have 1% regulation, and you achieve that on the 12V rail up until 45A, then that's your limit. If the parts and topology can provide 55A @ 2% V-reg, or even 65A at 3.5%, then you could choose 55A as the label number and 65A as the OPP cutoff, for example...

    As for temperature ratings... Well temperature influences the internal resistance of the rectifiers as well as the wires and traces. At a certain point you have to derate the parts due to this, and that calculates into the above points about target v-reg and absolute limit (before breakdown). Basically the manufacturer only guarantees the load table to be correct at or under the rated temps.
    Careful what you wish for... You just might get it.

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    Default

    Makes sense, thank you!

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