SOT sizes - Page 1
Forum section: electronics / beginners

author: bitman
author_rank: Unknown
timestamp: December 22, 2018, 08:28:42 pm
content: Is there a good chart where I can figure out what SOT sizes are available? Or rather, how they relate to one another? This pagehttps://en.wikipedia.org/wiki/Small-outline_transistorconfuses me.I needed to replace a DMMT5401 which had gone bad on my Raspberry Pi. I ordered SOT26 which was the smallest I could find, but it turns out to be almost twice as large as the original and is a hard fit in the same space. When I try to find out what "twice as small" would be, I don't get consistent responses, SOT23 comes in all kinds of odd derivations of 23 and I have no clue if that makes a difference. What I would like to do is measure the old component and determine what size it is.On a different note, searching on something SOT-23* on Digikey only gives me "obsolete" versions of this dual BJT - I wonder if that's just this component or that size just makes no sense? (It's very very small - I can imagine the issues getting something that small soldered on correctly).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 23, 2018, 01:02:33 am
content: Technically, this should do,https://www.diodes.com/design/support/packaging/diodes-packaging/diodes-package-outlines-and-pad-layouts/but it's rather verbose for a beginner question.Oddly, I have a (promotional?) card hanging on the wall of my cube with examples of the most common packages shrink-wrapped to it. I don't remember its title, and don't see a picture of one online, offhand. Hmm.If it helps, SOT-23 is almost always SOT-23. Digikey is very good about collecting the various mfg-specific designations into the right package. The higher numbers and letters and gibberish designations tend to be the microscopic unsolderable packages, which you'll probably want to avoid as a beginner.If all else fails, read the datasheet and check the dimensions. Designations don't mean a thing, what did they actually make?And yes, shopping for, and footprinting, components is no easier as a professional. Welcome to the real world...Tim

author: Nerull
author_rank: Frequent Contributor
timestamp: December 23, 2018, 01:55:15 am
content: SOT-23 is an extremely common size for transistors, it's certainly not "too small to solder".SOT-26 is just another name for a 6 pin SOT-23U14 on this board is the DDMT5401, and it looks like SOT-23 to me, and is about twice the size as the smaller SOT-523 transistors on the board.

author: bitman
author_rank: Unknown
timestamp: December 23, 2018, 03:07:03 am
content: Quote from: Nerull on December 23, 2018, 01:55:15 amThat's the B+ model - the B model (see attached) is using a much smaller version. I've soldered those small suckers before - it's not impossible - it's just not easy. You really have to watch for temperature and airflow but it's workable.

author: spec
author_rank: Frequent Contributor
timestamp: December 23, 2018, 08:31:30 am
content: Hi bitmanQuote from: bitman on December 22, 2018, 08:28:42 pmQuote from: bitman on December 23, 2018, 03:07:03 amThe chip that you want to replace U14 is the BCM857BS, which has an SOT363 case (same function as the DMMT5401).https://assets.nexperia.com/documents/data-sheet/BCM857BV_BS_DS.pdfhttps://www.diodes.com/assets/Datasheets/BCM857BS.pdfI think this is the circuit for your Pi, which must be a B3 model:https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_3b_1p2_reduced.pdfAs for rationalizing/understanding surface-mount case sizes, pin-outs, etc, forget it. It is a complete shambles in all respects, and is the cause of endless confusion, both in the amateur and professional worlds. The situation is a disgrace.

author: fouad2008
author_rank: Newbie
timestamp: December 23, 2018, 12:05:05 pm
content: Quote from: spec on December 23, 2018, 08:31:30 amMy first bench PSU was a single lead like yours are. That served me well for about a year or so, but slowly things started getting more complex and I needed to do negative voltages and other stuff, so I ended up having to purchase a second PSU with 3 outputs. While most of my stuff is very low voltage, the 3 feed allows you to do really cool things on the bread-board

author: t1d
author_rank: Super Contributor
timestamp: December 23, 2018, 12:18:18 pm
content: There are many, many, manufacturers of "electronic component rulers." They vary, greatly, with the type of information they each provide... component types, mounting hole sizes, etc... and price. So, you have to know what types of components you are most likely to be working with, to make a purchase decision... Here are Ebay examples, because they are likely to be the cheapest... But, some are down-right pricey, IMO, for what they are...https://www.ebay.com/sch/i.html?_from=R40&_nkw=electronic+component+ruler&_sacat=0&_sop=15&rt=nc&LH_BIN=1

author: bitman
author_rank: Unknown
timestamp: December 23, 2018, 03:58:13 pm
content: Quote from: spec on December 23, 2018, 08:31:30 amThat's what I'm finding out. The confusion I have/had on Wikipedia was all the different "sizes" that seem to cover the same unit size. I think I finally figured out how to read it, so by measuring the component I can "guestimate" the size I need.Thanks for explaining.

author: bitman
author_rank: Unknown
timestamp: December 23, 2018, 04:02:50 pm
content: Quote from: fouad2008 on December 23, 2018, 12:05:05 pmWhy are you quoting my post from a different thread as your own? I noticed you posted another of my posts in a different thread too as if it was written by you?