Question from a new user - possibly fake Mosfets - Page 1
Forum section: electronics / beginners

author: Chalcogenide
author_rank: Regular Contributor
timestamp: December 04, 2015, 07:43:17 pm
content: Hello everybody,I am student of Electronics Engineering in Milan, Italy, and a fan of only giving negative feedback :-)I have been lurking around for quite some time but have just registered to ask you an opinion about a small lot of NMOS that I have just received from China (yes, I know - but I'm not making any mission critical device so I go for the cheapest stuff for my home experiments).Now, the "device under question" should be an IRL540N, logic level family, good for a few tens of amps. (Datasheethttp://www.irf.com/product-info/datasheets/data/irl540n.pdf), but the markings didn't look all that legit, so...I first put one of these Mosfets on an el cheapo component tester that reported a 3.5V threshold (but it's not accurate in any way) - this definitely rang a bell, since the IRL series should have a threshold below 2V.I then connected the FET in transdiode configuration, injecting some current via a self-made constant current source, which I was able to dial down to a minimum of 290uA (close enough to the specified 250uA in the datasheet) and got a reading of 2.88V.I then dialed up the current, keeping the transistor in transdiode configuration (but only connecting it briefly, not to overheat it), and found the curve attached to the post.I guess that I got a batch of fake devices, didn't I?From the curve they look similar to an IRF540, possibly. A real IRL540N should be pushing more than 10A at 4V-ish Vgs.I also attached a picture showing the markings as well as I could.

author: c4757p
author_rank: Super Contributor
timestamp: December 04, 2015, 07:49:22 pm
content: Agreed, they behave like IRF540. Also, the font on the markings is different from all the International Rectifier devices I've had.

author: M4trix
author_rank: Frequent Contributor
timestamp: December 04, 2015, 08:05:43 pm
content: Well, there's no other solution... smash it carefully with a hammer and let us see how the die looks like. If it's covered with white glue, it's 100% fake.

author: Chalcogenide
author_rank: Regular Contributor
timestamp: December 04, 2015, 08:18:43 pm
content: I might as well do it with one of them, after I get the money back from the seller.I have a 2kg hammer that should do the trick.Or I could slowly crack it open in a vice...

author: fivefish
author_rank: Frequent Contributor
timestamp: December 04, 2015, 10:04:15 pm
content: MOSFETs you buy from eBay/China don't achieve the full rating of the part# they're supposed to be. They're all damn fakes.

author: dom0
author_rank: Super Contributor
timestamp: December 04, 2015, 10:22:11 pm
content: Components bought from Chinese suppliers on eBay are very often fakes, especially for easy to fake parts (e.g. transistors).It's simply not worth buying these. Check if there are really no active electronics suppliers in your country.

author: Chalcogenide
author_rank: Regular Contributor
timestamp: December 04, 2015, 10:50:40 pm
content: I would never use Chinese mosfets in any critical circuit, but I just couldn't resist the low price. I just needed some jellybean logic level mosfets for a couple of amps worth of current.However, I assumed that fake devices would have lower curent rating and/or breakdown voltage, but at least be of the same kind of the real one. I mean, if I were to drive these "IRL" mosfets on a 3.3V logic, I would hardly get enogh current to light an LED, vs 10+A on a real one.This kind of fake is pretty darn easy to spot.

author: Ian.M
author_rank: Super Contributor
timestamp: December 04, 2015, 11:03:26 pm
content: ASS-U-ME.You got the high quality fakes. At least they started off with something approximating to an N channel power MOSFET rather than some random river-washed TO-220 BJT, no two the same.

author: M4trix
author_rank: Frequent Contributor
timestamp: December 05, 2015, 12:03:26 am
content: Quote from: fivefish on December 04, 2015, 10:04:15 pmWell, we can't say all are fakes. There are some honest China/Hong Kong sellers who sell only genuine stuff. So far I found one reliable seller, Electronics Salon/Audiowind. I was often buying from him bunch of power transistors like 2SC3264/2SA1295, 2SC5200/2SA1943 and IRFP240/IRFP9240 etc. All transistors tested under heavy load. No problems at all ! Even hammered some, just in case! Well, it's still the best way so far to see if it's fake or nothttp://stores.ebay.com/Electronics-Salon

author: fivefish
author_rank: Frequent Contributor
timestamp: December 05, 2015, 12:16:51 am
content: You're right. I generalized by using the word "ALL".Amended: Majority 99.99999% of them are fakes/rebadged/relabeled.

author: Falcon69
author_rank: Super Contributor
timestamp: December 05, 2015, 06:31:46 am
content: Quote from: M4trix on December 04, 2015, 08:05:43 pmOr smash it, and if there is a SIP-3 (TO-92?) cased mosfet in there, then let us know. 100% sure it's fake then.

author: Chalcogenide
author_rank: Regular Contributor
timestamp: December 05, 2015, 10:37:00 am
content: As per request, I tried to smash one of those fake transistors (the seller refunded me instantly, so he clearly knew he was selling crap), but it turns out that the 2 kg hammer was a bit too much and I couldn't even find the die within the powdered stuff. Accidental Widlarization, I guess.So I took a second sample to destroy with a much smaller hammer, and while the die still shattered, it can be seen from the remainance that at least the die looks like a resonable size, and that it is actually a DMOS, since the drain is contacted directly at the bottom. So I guess that I was lucky since now I'm left with 18 free unknown-but-probably-good-for-low-power-stuff mosfets.I took the macro shot with a Canon 40D, 50mm 1.8 @f/8 with a 34mm extension tube.

author: M4trix
author_rank: Frequent Contributor
timestamp: December 05, 2015, 11:40:26 am
content: Hmm, looks like genuine. Dunno what to suggest anymore.

author: Chalcogenide
author_rank: Regular Contributor
timestamp: December 05, 2015, 12:22:28 pm
content: I even tested them to check the leakage current at 100V (ish), and I got less than 10uA (room temperature), so my guess of them being relabeled IRF540 (or something in the same ballpark) may be true after all.They are definitely not IRL due to high threshold voltage, but at least they appear to meet their voltage specification.Being still a reasonable quality transistor might also explain why the seller reviews were OK... Most people using them for low power Arduino-ish stuff woldn't bother to check for the threshold voltage, and as long as they don't overheat they may fall unnoticed.

author: ice595
author_rank: Regular Contributor
timestamp: April 25, 2020, 07:01:28 pm
content: at least they gave you the right kind of crappy MOSFET, I got a P channel MOSFET that was labeled as an IRF540!!!