Finding datasheet for this MOSFET! (SMS5408 0932)

mosfet

This component carries the markings SMS5408 0932 is busted! It is part of a 1000W psu of a flagship subwoofer of a (very) respectable brand, and I can't find any datasheet at all for it!

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I assume it is a MOSFET because of the G,D and S markings on PCB. Only thing I could find for the SMS was this company:

http://www.siliconmicrosystems.co.uk/contact.html

that seems to provide asic services, doesn't seem to manufacture components. Also couldn't find any reference for 5408 except diodes.

Usual websites like alldatasheet, datasheetcatalog, etc didn't bring anything up. Contacting the manufacturer is no good, they've sent me another unit so no one would have to worry about repairing anything. But I really won't let this off because I can't find a replacing mosfet!! 😉

New image (PCB backside):

PCB backside

Best Answer

If you see G,D and S is likely to be a MOSFET, not a BJT. So this is a precious indication and you are very lucky to find it because these markings are very rare. The other good news is that it's 10 years old, not too new and not too old.

Two things you must find out:

  1. Voltage on the D pin or, on the S pin if D is ground or the low side. And vice versa. You can check the voltage rating of the capacitors which are connected to it, if any. And use the same or higher for the MOSFET. If you can't know the voltage, use 300V or more.
  2. The maximum current which could possibly go through the MOSFET between D and S. This is more difficult. If you know the voltage, it can't be more than 1000W divided by the voltage on D or S (depending which one is not the low side). So take the highest value available.

The absolute maximum voltage rated for G in the datasheet will likely to be same on every MOSFET you will find. Still, check that it's not lower than 20V (You never know). (always read the datasheet pdf before buying)

Frequency shouldn't be an issue with modern MOSFETs. That's why 10 years old is a good age. Any newer MOSFET will be better than the original, granted that you can find the same specification or better. I would even advise NOT to try to find the exact original part since it failed...

Attention: The same model can be fabricated in different packages: D-PAK or something else but the THT variant is often available. Check the datasheet for the exact product code (the last letters define the package, usually). Don't discard or select a model based on the picture on the vendor website.