Which Mosfet it could be? - Page 1
Forum section: electronics / beginners

author: tpd
author_rank: Contributor
timestamp: April 14, 2024, 09:04:26 am
content: Hi,In pics there is an unknown Mosfet, it has body of plastic and text at the front side of it is covered (missing) with black sticker (maybe it is just transistor itself, it can't be peeled off).Next to it 2N70 Mosfet, a PCB of a cheap chinese switcher 5V 6 A is in question. I suppose unknown Mosfet is used to avoid repairment by "nasty people".Can someone say which Mosfet it could be, or to suggest a possible replacement for it?Thanks

author: Ian.M
author_rank: Super Contributor
timestamp: April 14, 2024, 09:30:45 am
content: Impossible to tell. There are lots of semiconductors in isolated TO-220 packages, not just MOSFETs. The 'D6' marking next to it suggests it *may* be a diode or dual diode . . .

author: tpd
author_rank: Contributor
timestamp: April 14, 2024, 09:53:03 am
content: Quote from: Ian.M on April 14, 2024, 09:30:45 amThanks, I didn't pay attention to D6 marking.

author: Ian.M
author_rank: Super Contributor
timestamp: April 14, 2024, 11:36:22 am
content: Looking at it more closely, J2 shorts its outer legs, so its definitely a dual diode, with both sections in parallel for a higher current rating. Desolder the middle pin to isolate it and it should measure as a diode between that and the joined end pins. In circuit measurements are complicated by the winding feeding it providing a path to ground and the reservoir capacitor it feeds. Its probably a Schottky so expect Vf <0.5V

author: Psi
author_rank: Super Contributor
timestamp: April 14, 2024, 11:53:59 am
content: Being a diode is good, it's much easier to guess at what sort of diode will work than it is trying to guess a replacement transistor.

author: tpd
author_rank: Contributor
timestamp: April 14, 2024, 11:56:10 am
content: Quote from: Psi on April 14, 2024, 11:53:59 amFor me it is the same - I can't guess the sort niether of them.

author: Psi
author_rank: Super Contributor
timestamp: April 14, 2024, 12:03:08 pm
content: For a replacement diode you really only need to know* Roughly what amps it needs to handle. And you can just overspec it to be safe, just costs little more* Is it Schottky or silicone diode, if it's on the output side of a switchmode its going to be Schottky for speed and low vdrop. If its part of a input mains bridge rectifier it could be either but probably doesn't matter anyway. And since its a dual package one of them is probably ok so you can just test it to see if it's Schottky or silicone* What voltage does it need to handle. Easy to figure out based on voltage of the circuit plus a safety margin. Again plenty of room to overspec it.Then just need to source one with the same diode common terminal / pinout. And insulated case of course too.

author: Ian.M
author_rank: Super Contributor
timestamp: April 14, 2024, 01:01:28 pm
content: Its certainly possible to find a replacement that way, but I'd bet that as there are no signs of physical damage, that whatever measurements it failed as a 'MOSFET' are correct for a diode, so its probably fine. The only reason to pull it and investigate further is if its actually shorted.

author: tpd
author_rank: Contributor
timestamp: April 15, 2024, 12:23:09 pm
content: It is not Mosfet, it is MBRF10100CT Schottky Rectifier

author: Ian.M
author_rank: Super Contributor
timestamp: April 15, 2024, 01:16:50 pm
content: How did you determine that part number? Did you manage to see it on the surface of the component, or did you find a schematic?

author: tpd
author_rank: Contributor
timestamp: April 15, 2024, 01:25:42 pm
content: Quote from: Ian.M on April 15, 2024, 01:16:50 pmI bought another switcher and desoldered rectifier after I saw that it is labeled. I bought it so I can compare destroyed componets in exploded and a new one.I am practicing repairment on it.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: April 15, 2024, 01:41:48 pm
content: "I bought another switcher and desoldered rectifier after I saw that it is labeled. I bought it so I can compare destroyed componets in exploded and a new one.I am practicing repairment on it"I like his thinking