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[The_Almighty_Bacon_Lord]

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[Andy Watson]

The limitation is probably due to the choice of the value of the inductor. Higher voltage means that the current in the inductor will rise quicker - the regulator IC must be able to react fast enough to control that current, i.e. turn-off. The value of the inductor has probably been chosen to optimise other operating parameters - allowing for a high voltage input would be a compromise too far. You would have to reverse-engineer the schematic know for sure.

[Audioguru]

It is Chinese and it is cheap. Then maybe its parts are poor copies of the real ones. Maybe its parts are rejected real ones that fail at more than 30V.
Maybe its heatsink is big enough to cool its hot parts at 10A only if the voltage is at 30V or less. Try 38V input but a load current of no more than 7.9A.

[Brumby]

It could be because of circuit design where the choice of components means something would exceed some parameter in it's SAO ... or it could be something as stupidly simple as the manufacturer having a bucket load of 35V caps and they limited the circuit to 30V so they could use them.

The bottom line is - just because a component can handle a range of parameters doesn't mean it will always be used to those limits.



I'll go for a thermal limitation.  (Cheap heatsink with questionable mounting.)