I want to power this Nucleo board by a 5V external source using E5V pin. But regarding the external power supply choice there is the following section:

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I was planning to use this 5V SMPS. I didn't get what is meant by SELV in this case and whether this supply can be used. Can someone explain this in plain language?


1 Answer 1


SELV means Separated or Safety Extra-Low Voltage.

The manual just means you must use a isolated and safe power supply so you don't damage your equipment or get electrocuted by using for example non-isolated supply.

So basically, it is common sense, but it is good to explictly mention that in the manual, because if you don't know what you are doing, and use an non-isolated supply, and you damage something or get killed, it means board manufacturer has no liability because you used it against warnings in the manual.

The power supply is safe and isolated.

  • \$\begingroup\$ Kind of depends if these boards are sold as stand-alone products or as evaluation boards. Engineering prototypes are exempt from things like the Low Voltage Directive. As in: you are assumed to know what you are doing. I don't think the board manufacturer has much in the way of legal responsibility at all, as long as they are clear with it being an evaluation board. \$\endgroup\$
    – Lundin
    Sep 6 at 13:11
  • \$\begingroup\$ @Lundin ST makes it clear it is for evaluation only. They specifically forbid using eval boards as part of a commercial or household products and if your prototype has one, the prototype should be used by you only, selling/leasing/lending it to another party is forbidden. I understand it is not their responsibility, but they have to make clear it isn't, as they could get bad publicity if someone uses dev boards commercially and the product happens to be dangerous. \$\endgroup\$
    – Justme
    Sep 6 at 13:26

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