noob woes: finding an SMD inductor? - Page 1
Forum section: electronics / beginners

author: funbags
author_rank: Contributor
timestamp: April 16, 2018, 05:33:59 pm
content: Hey All,I'm trying to source an SMD inductor (15uH at 1A), but I'm beginning to believe that every manufacturer has different package dimensions. At least I found very little consistency.I'm totally new to this and have just been doing PCB design as a hobby for the last 6 months. I decided to try my hand at making a 12v to 5v step down power regulator with a mp1584en (to hook up to a car battery, and be able to power 1 USB device). The Data sheet tells me the value, and the relative pad dimensions, but not much more than that.When designing the PCB, is there a relatively generic pad design/dimensions that will get me the most versatility for different mnfg's specs? Like 4040/1515? I worry because sourcing the parts that I need has been a battle in the past, and I don't want to be stuck with pads that don't exactly fit the part I have to end up using because my first choice is out of stock.Thanks for any help.

author: ovnr
author_rank: Frequent Contributor
timestamp: April 16, 2018, 05:55:48 pm
content: It's not like you're mass-manufacturing these things. Plop down some pads that are close enough - too big is better than too small - and just deal with it. You don't have to have exactly right pads for large power inductors.

author: funbags
author_rank: Contributor
timestamp: April 16, 2018, 06:39:18 pm
content: Thanks for the input, ovnr. I think you're right. I'll just put down pads I think are big enough... it just doesnt sit well with my OCD. I enjoy looking at the boards after their done, and small errors/hackishness like that drive me crazy.I was just wondering how a professional would go about it? Not that I'll be able to do it that way.. hahaThanks!

author: dmills
author_rank: Super Contributor
timestamp: April 16, 2018, 06:51:44 pm
content: Inductors are a pain in the arse.My usual approach is to find three alternatives with Automotive Qualification (Tends to mean they will stay around a while) from ideally three different vendors (None of which is F&$&!*g Multicomp!) with footprints that I can combine into something that will work.I still get burned by long lead times semi regularly.Wurth have been good to me lately, but it really is a 'who has pissed you off least recently' thing, and Wurth tends to be very expensive thru distribution but not that bad direct.Regards, Dan.

author: funbags
author_rank: Contributor
timestamp: April 16, 2018, 07:22:44 pm
content: awesome, dmills! Thanks for the tip. I'll check out Wurth!I know what you mean. In my noobishness I made the mistake or drawing pads for a PZT3904, but used the pin order from the through hole 2N3904 version, but actually ordered mmb3904 because everything else was out of stock, and on a 6 week lead, and I didnt pay close enough attention to the model number... hopefully a lesson I wont learn twice. I now have 100 transistors I wont be using. hahahaThanks!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 16, 2018, 07:48:17 pm
content: FWIW, the IPC acknowledges that there is no universal inductor footprint, so you have to apply their footprint design rules carefully to come up with a reasonable footprint.In smaller values, conventional chip sizes are typical. 0603, 0805, 1210, 1812; but also nearby sizes, with different terminations (usually bottom pads instead of wraparound metallization), 0806, 1212, 1816, etc.For footprints, bigger is usually better, yes. As long as you can get a soldering iron around the biggest part you expect to use, you're fine!Also watch out for manufacturers using different units for their numbering schemes: Vishay IHLP family are imperial (IHLP2525xxx = 0.25" / 6.3mm square), others are metric (Taiyo Yuden NRS6045 = 6.0 mm square, 4.5mm high). Just name your footprints consistently (choose in or mm)...Tim