MOSFET with Drain, Gate, Source pinout? - Page 1
Forum section: electronics / beginners

author: JaseG
author_rank: Contributor
timestamp: December 10, 2015, 09:34:31 pm
content: Hi,I've designed and printed a circuit board which uses a few mosfets but I messed up the footprint on them. Instead of Gate Drain Source (from left to right), it is Drain, Gate, Source.Does anyone know of a N-Channel MOSFET that has the pinout to suit? D, G, S. The gate needs to have a low enough Vgs to work with logic level input and needs to be able to pass at least 5v @ 1.5amps from Drain to Source.Any help would be greatly appreciated!Cheers,Jasep.s. Here's the board - it looks sexy so I thought i'd share. Too bad it doesn't work.http://jasongilholme.com/wordpress/wp-content/uploads/2015/12/wpid-wp-1449695505474.jpg

author: dom0
author_rank: Super Contributor
timestamp: December 10, 2015, 09:54:02 pm
content: Won't happen with normal vertical power FETs. Lateral ones might have a different pin out, but they're rare today.

author: Zero999
author_rank: Super Contributor
timestamp: December 10, 2015, 10:00:34 pm
content: In other words, the reason why MOSFETs have this type of pin out is the way they're physically constructed so, unless you use a different type of MOSFET, you won't get a different pin out.

author: JaseG
author_rank: Contributor
timestamp: December 10, 2015, 10:05:19 pm
content: doh! That's understandable.I have some other non-critical design issues with the board anyway so it was going to have a rev B at some point.Danke für dein hilfe!

author: Halfdead
author_rank: Contributor
timestamp: December 10, 2015, 10:07:27 pm
content: I'd just trim the leads and solder some solid wires on.

author: Ian.M
author_rank: Super Contributor
timestamp: December 10, 2015, 10:08:21 pm
content: Plenty of space, good size pads, so why not cut and patch it?

author: JaseG
author_rank: Contributor
timestamp: December 10, 2015, 10:15:58 pm
content: Quote from: Ian.M on December 10, 2015, 10:08:21 pmIt's definitely re-workable. Ultimately I'd like a non hacked final version but I'll hack this one to ensure that the rest of the circuit works. It's quite simple (yet i still managed to screw it up! haha)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 11, 2015, 02:06:38 am
content: Twist the leads around (use some spaghetti tube if you can't finagle the bends by pliers alone).Here's a hack I did in an SMPS. Boned the TL431 pinout somehow. TO-92's have plenty of lead length though.Tim

author: Ian.M
author_rank: Super Contributor
timestamp: December 11, 2015, 02:17:37 am
content: Why mangle the MOSFETs? If you are a parsimonious git of expatriate Scots ancestry like myself, you will patch the board with the expectation that if all goes well you will be able to transplant the MOSFETs cmpete with heatsinks to the final board.

author: JaseG
author_rank: Contributor
timestamp: December 11, 2015, 02:44:59 am
content: Quote from: Ian.M on December 11, 2015, 02:17:37 amYeah, I agree completely. My preference is to maintain the mosfet & heatsink condition and hack the board. it's already busted anyway and theres no need to break a perfectly good fet. It did nothing wrong.I'm a noob and never done it before but I'd imagine it's just a matter of cutting the traces that are no good and replacing them with some jumper wires. Is that right? Preferably on the back side of the board to hide the hackery as much as possible. What people don't know won't hurt them. :p

author: alsetalokin4017
author_rank: Super Contributor
timestamp: December 11, 2015, 03:17:05 am
content: 2n7000 in TO-92 is DGS.https://www.fairchildsemi.com/datasheets/2N/2N7000.pdf

author: JaseG
author_rank: Contributor
timestamp: December 11, 2015, 04:14:45 am
content: Quote from: alsetalokin4017 on December 11, 2015, 03:17:05 amoooo thanks!!I don't think i'd use this in the final design because i'd be pushing it's upper limits for current through put. I would also have to figure out a way of heatsinking that thing. It's 300+ degrees per watt as well! ouch.

author: miguelvp
author_rank: Super Contributor
timestamp: December 11, 2015, 04:16:06 am
content: Or mount them on the other side of the board, that is if you can mount the heatsinks under as well.Edit, of course you probably have to flip the board to install it where it was intended (hopefully there is clearance for the other components once the board is flipped.Edit2: nevermind, Drain, Gate, Source I though you just flipped the footprint, my bad.

author: Richard Head
author_rank: Frequent Contributor
timestamp: December 11, 2015, 05:43:41 am
content: Therefore, it is either GDS or SDG. The industry prefers GDS/BCE configuration, for whatever reason over SDG/ECB configuration.Unless you're using RF MOSFETs such as the RD range where the sequence is GSD so that the tab is at ground potential.

author: Zero999
author_rank: Super Contributor
timestamp: December 11, 2015, 08:47:57 am
content: Quote from: JaseG on December 11, 2015, 04:14:45 amYes, the old 2N7000 is really no good for power. It has an on resistance of 5 Ohm when the gate voltage is 10V, a maximum continuous current of 200mA. When the gate voltage is just 4.5V, the resistance increases to 6 Ohm and the drain current is only specified to 75mA.https://www.fairchildsemi.com/datasheets/2N/2N7000.pdfThe 2N7000 is only good for small signal amplifiers and as an analogue switch.

author: dom0
author_rank: Super Contributor
timestamp: December 11, 2015, 09:05:14 am
content: Quote from: Richard Head on December 11, 2015, 05:43:41 amRF MOSFETs are probably lateral FETs with a single or very few parallel cells...--ECB <-> BCE is arbitrary. BD139/140 are ECB for example.I don't use TO-3, how is the "pin out" situation there? The pins are probably arbitrary, too... ?

author: amyk
author_rank: Super Contributor
timestamp: December 11, 2015, 10:32:19 am
content: Quote from: dom0 on December 11, 2015, 09:05:14 amThe substrate is always the case, so it could never be a base or gate.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 11, 2015, 07:42:13 pm
content: Some parts, mostly RF, are arranged 'backwards', with E/S on the case and B/G and C/D on leads. I understand some of these are actually done with the substrate being E/S, though I'm not real clear on how.All power packages, that I'm aware of, have the center pin not only connected to the tab/case, but made as a part of it (from the same stamping or whatever). This is awkward for some components (e.g., TO-263-5 case gate drivers; the IXDD614CI for example has the 'selling point' of being grounded case, unlike others, IIRC)."EBC" TO-92s I guess were common enough that they went to the trouble to make a suitable leadframe: if you've ever cracked one open, you should see a coined blob on the side (collector) terminal -- just like a power device, except the back plate is fully encapsulated. (There's also a TO-92 variant with the tab brought out, TO-237. See also the TO-202, which is like a TO-220 with a similarly flimsy tab.)Tim