Replacement for MOSFET 2SK3502 in Dell Monitor(2407WFPb) PSU - Page 1
Forum section: electronics / repair

author: Trurl
author_rank: Regular Contributor
timestamp: January 01, 2020, 02:20:07 pm
content: Recently my Dell Monitor(2407WFPb) PSU failed. Many parts need to be replaced. One part seems to be not available(at least with reputable distributors like Digikey. There are offerings on AliExpress, Ebay, Amazon, etc. but I am concerned that these may be fakes).This part is the power MOSFET2SK3502byFuji Electric.I have searched and narrowed down to 2 possible alternatives:1. ON Semiconductor(Fairchild)FDPF17N60NT2. Alpha & OmegaAOTF12T60P1. Would any ‘alternative’ mentioned above be suitable for the task?2. If both are suitable which would be the better choice and why?[Notes and References]1. Dell Monitor(2407WFPb) Schematic-Diagramhttps://www.scribd.com/doc/207782153/Dell-2407-WFP-Power-Supply-Rev-A11-Schematic-DiagramNote:In the schematic, the MOSFET’s part number is Q651 and is located on the 1st page, to the right of the PFC (IC651) connected to the GD(Gate Drive) pin.2. Original part datasheetsA.2SK3502-01MR(from Fuji Electric’s website)https://americas.fujielectric.com/files/2SK3502-01MR.PDFB.2SK3502(from ALLDATASHEET.COM) Note: The specs are slightly different(lower) than the above, and I’m not sure if this is an official datasheet ‘approved’ by Fuji Electric. Some notable difference is 12A vs 10A (Continuous Drain Current), and 70W vs 50W (Max Power Dissipation)https://html.alldatasheet.com/html-pdf/88508/FUJI/2SK3502/81/1/2SK3502.html3. Possible alternative parts datasheetsA. ON Semiconductor(Fairchild)FDPF17N60NThttps://www.onsemi.com/pub/Collateral/FDPF17N60NT-D.pdfB. Alpha & OmegaAOTF12T60Phttp://aosmd.com/res/data_sheets/AOTF12T60P.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 01, 2020, 03:04:48 pm
content: I would prefer the AOS part: closer Rds(on), Qg(tot) and meets or exceeds everything else. The Fairchild part is a little too big (higher Qg, lower Rds(on)) but there may be a similar, next-size-down version which would also be fine.Don't forget to check the gate drive circuitry, I imagine the controller/driver is toast but don't overlook resistors and stuff either. Transistors fail as three-way shorts, so 200V+ goes everywhere.Tim

author: Trurl
author_rank: Regular Contributor
timestamp: January 01, 2020, 03:22:14 pm
content: Much thanks Tim!Yeah, my first option(by it showing up first in a search) was the AOS, but the 70W vs 50W power dissipation rating kept me a little nervous and searching for other options with a higher power dissipation rating (closer to the Fuji Electric's 70W or more).If you or anyone else has an opinion on the power dissipation difference, comments would be welcome.Thanks!P.S.If anyone can confirm whether the ALLDATASHEET.COM's datasheet for the 2SK3502 (indicating power dissipation as 50W) is indeed legit, that would be great, as I can then just go ahead with the Alpha & Omega AOTF12T60P.

author: keymaster
author_rank: Regular Contributor
timestamp: January 01, 2020, 05:24:01 pm
content: i thing that the package is limiting all of them at 35watt.70 watt from a to-220f package is a bit to much .the real number is hiding in the graphs of the datasheet .

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 01, 2020, 05:43:30 pm
content: If that poor thing is running more than about 20W, it would have died a hell of a lot sooner.Yes, 30W is about the practical limit for fullpacks; and that assumes excellent heatsinking. If it's bolted to a small heatsink with no fan, maybe 5 or 10W is typical. RthJC of the component will make much less difference in that case -- that is, because RthHS-A is much greater.Tim

author: Trurl
author_rank: Regular Contributor
timestamp: January 01, 2020, 06:39:50 pm
content: keymaster & Tim,Thank ya'll so much for easin' my nerves.I feel much more at ease about goin' ahead with the Alpha & Omega AOTF12T60P (50W) MOSFET.The monitor's PSU lasted about 12 years, so I cannot complain. Apparently the reason that these PSUs fail is usually(as is the case with mine) because of the main(450V 120uF) capacitor eventually leakin' from base of the positive lead then POOF (fails), which causes a domino effect knocking out sooo many other parts including the power MOSFET mentioned.Now I can finish up by movin' onto shoppin' for all the resistors out of tolerance!Thanks again!

author: Trurl
author_rank: Regular Contributor
timestamp: January 02, 2020, 05:55:34 pm
content: With the pointers received from keymaster and Tim,I reexamined my initial choice(s) for the other MOSFET(Q601 : Fuji 2SK3548-01SC)https://www.datasheetq.com/datasheet-download/139786/1/Fuji/2SK3548which also needs an alternative replacement.My initial choices were:ON Semi(Fairchild) FQA11N90_F109https://www.onsemi.com/pub/Collateral/FQA11N90_F109-D.PDForON Semi(Fairchild) FQA11N90C-F109https://www.onsemi.com/pub/Collateral/FQA11N90C_F109-D.PDFThe options above were considered on 'redundancy'(slightly higher specs) such as 11A Drain Current vs 10A , compared with the original 2SK3548-01SC, but I noticed that their Rds(On) are quite lower and Qg are quite higher.So now I'm considering a slightly more conservative sibling model which is rated at 9A Drain Current vs 10A, but the Rds(On) and Qg are much closer to the original.ON Semi(Fairchild) FQA9N90C_F109https://www.onsemi.com/pub/Collateral/FQA9N90C_F109-D.PDFI'm thinkin' that the 9A Drain Current spec is conservative as there are references to 11A in the Turn On Times and Gate Charges Test Conditions.Oh and the thermal specs seem to be better with the alternatives so that is not a concern for this part.I think the 9A version would be a closer match to the original part than the 11A version. What do you think?

author: keymaster
author_rank: Regular Contributor
timestamp: January 10, 2020, 07:21:18 pm
content: yes the 9A (FQA9N90C_F109 ) is a better match to the original , the other two are a bit more difficult to drive .