[SOLVED] Is it ok to substitute XF smd with 1G smd transistor? - Page 1
Forum section: electronics / repair

author: Chriss
author_rank: Frequent Contributor
timestamp: November 07, 2020, 07:48:30 pm
content: Hi!I'm repairing a sort of small relay controlling board where the drivers are some sort of XF smd transistors.One or two outputs are gone and the transistors are shorted out.I'm not really sure does these XF labeled part is maybe an N type mosfet?At the moment, I have in my stock 1G smd transistors which should be BC847C transistors if I'm not wrong.Is that ok to substitute these XF transistors with my 1G transistors?Or is it a better option to use a BC337 transistor instead the BC847C one?Thank you for any suggestion or help.

author: Yansi
author_rank: Super Contributor
timestamp: November 07, 2020, 07:51:10 pm
content: Based on the circuitry around, identify what part of circuit it is in."XF" marked SOT23 device can be anything from a zener diode up to an IC.http://www.s-manuals.com/smd/xfAlso, if it got faulty, there are probably more faults in the circuitry around. So you need to investigate further.

author: Chriss
author_rank: Frequent Contributor
timestamp: November 07, 2020, 08:16:59 pm
content: Thanks for the quick replay, I stumbled also in that infos like you posted. It could be anything based just by the marking.After a while of investigation on the board, definitely it is driving the relais witch are thes one from these datasheet:https://media.digikey.com/pdf/Data%20Sheets/Panasonic%20Electric%20Works%20PDFs/CV(ACV)_Series.pdfThe marking on the board where the XF part's are ( there are around 10 relays on the board ) are labeled wit Qxx ( like Q12, Q28... ).That told me does it should be a sort of transistor or mosfet.If I investigate forder and compare the legs orientation of my XF part with one of the datasheet from here:http://www.s-manuals.com/pdf/datasheet/r/n/rn1101f-rn1106f_toshiba.pdfThen I get a circuit like this:the B goes to the CPU output pin through a resistor.The E is connected to GND.The C is connected to the relay.And I know for sure does the cpu is switching gnd and the +12v is constantly on the relay coil other terminal.Based on this, this could be a sort of transistor but I'm a bit afraid cos the Ic = 100mA by the datasheet.In the datasheet of the relay it stand it will consume around 67 mA or 84 mA depending if the relay is fitted with a resistor or not.Maybe IC=100mA is a bit low...The part I repair is the fusebox in the engine bay from a Renault Clio 3.https://www.google.com/search?q=356%20231e&tbm=isch&tbs=rimg:CTAYpt_1Ed2_1_1Ycz1oVf7yM2x&hl=en&sa=X&ved=0CAIQrnZqFwoTCPDl-qKi8ewCFQAAAAAdAAAAABAH&biw=1263&bih=881

author: fzabkar
author_rank: Super Contributor
timestamp: November 07, 2020, 08:41:13 pm
content: Here's a possible candidate:2SK3408, NEC/Renesas, N-ch MOSFET for switching, 43V, 1A, 195mOhm Rdson, marking XF, SC-96:https://docs.rs-online.com/38c6/0900766b811ae31e.pdfThe datasheet dates back to 2003.

author: Chriss
author_rank: Frequent Contributor
timestamp: November 07, 2020, 09:08:14 pm
content: WoW!How Dave say "Bingo!"I would say you hit the head!Here is my circuit how it looks like.I think it is the same as the test circuit shown in the datasheet on page 2 "TEST CIRCUIT 2 GATE CHARGE"In my area it is complicated to get the 2SK3408 mosfet, can I substitute it with this one:https://www.mouser.at/datasheet/2/115/ZXMN6A07F-74814.pdfIt is much easier to order for me now.Thanks.

author: fzabkar
author_rank: Super Contributor
timestamp: November 07, 2020, 10:33:08 pm
content: The substitute seems OK to me. Just check whether there is a snubber diode across the relay coil.

author: Chriss
author_rank: Frequent Contributor
timestamp: November 12, 2020, 12:50:54 pm
content: Just to notify about my repairing progres of this device.The mentioned substitution and suggested part is fine to use in this circuit.Job done and the unit is working perfect.Thanks guys for helping.My best regards.

author: florentbr
author_rank: Contributor
timestamp: February 18, 2022, 09:08:12 pm
content: I had the exact same issue.The relay of a Renault Clio 3 was stuck closed, leaving the lights on.Thanks to this thread, I managed to identify the dead XF transistor (mosfet 2SK3408).I replaced it with a Si2308DS which is more widely available.What's strange is that the original relay ACV31012 had no flywheel diode or resistor and I didn't find any on the board.Since the relay was dead, I replaced it with a BOSCH 0986ah0090 (with 1k resistor on the coil).The original relay was drawing 70mA. The new relay is drawing 100mA.Since the Si2308DS supports up to 2A with a lower RDS(on), there's still plenty of room.