I was there searching for resistors the other day. In the past, my experience was that Mouser had a larger selection of R's, I don't know if that's still true.
Anyway I couldn't find what I wanted. (I've gotten spoiled by 0.1% R's, but above ~ 1 Meg they become expensive.)
George H.
On Mon, 28 Sep 2015 06:20:07 -0700 (PDT), George Herold Gave us:
For most designs, the cheap 1% stuff is quite sufficient.. In "spoiling" yourself, you also "spoiled" your grasp of proper engineering technique. Ooops.
Well in this case the 1% resistor will determine the error. (It's just this "silly" current source.) I've got a 0.1% voltage reference, and for higher ranges of current I'll have 0.1% R's. It's not a big deal to have the lower range less accurate. But it would be nice if it wasn't. For less than a buck I could put five 1 meg's in series. (You get addicted to all those 9's or 0's on the voltmeter during testing too... makes you feel like you know what you're doing :^)
George H.
The tempco will getcha on 0.1% thickfilms. We use mostly Susumu 0.1 and 0.05% thinfilm parts for precise stuff. They sell resistors at 25 and 10 PPM.
The Susumu resistors often come in weird values, and don't come in high values. But even the 25 PPM parts have typical TCs in the single digits.
One of my guys has found some high value "fine film" resistors rated for 25 PPM.
On Mon, 28 Sep 2015 07:04:09 -0700 (PDT), George Herold Gave us:
You could buy ten or a hundred 1% devices and 80% of them would test out at just as close, i.e. 0.1%
Yeah I always worry a bit about the TC values. Unless there is a plot on the data sheet you are not sure what to make of it. Is this guys 100 ppm better or worse than someone else's spec. (I'm not going to measure it!)
Good to know that the susumu's are typically better than the spec.
I was hand selecting (well a minion does it.) 10 Meg metal films, (100 ppm/C). But one gotcha I found was that the value goes up by a few ppt when you solder them onto the pcb.
No they don't. It's not like you'd expect. From my experience if you get a batch of 10Meg 1% MF resistors you'll find that they will mostly measure a bit high ... 0.4-0.6%. Which sorta makes sense if you think about setting up a resistor machine, and trimming the value till you get to the right number.. you'd make it stop when it was just a bit high. Anyway I think we found (maybe) 5% that were within 0.2% of the nominal resistance.
George H.
Are you sure you have explored all the abilities of the engine? Have your read their help section on it?
It only allows 100 filters, and it's happy to create over 100 filters for a reasonable search.
Have
No, I bail and go to Digikey, or to the manufacturers. Some of the manufacturers have decent search, some don't. The worst ones require me to open dozens of .pdf files to see what they have. Or force me to choose an application area, or make me decide if I want a precision opamp, or a fast opamp, or a general-purpose opamp.
As my old mentor Melvin Goldstein used to say, "the easiest thing in the world is not to sell."
Why would you stop when the value is still high? Are you saying the machine stops as soon as it is in the tolerance range?
I remember checking out an Asian MCU maker's web site and couldn't find any overview of their parts. They had charts with lots of part numbers in bubbles, but no info on what these parts had and those parts didn't. I emailed them asking for a selection guide and they told me to download the data sheets. They have all the info I was looking for. Yeah, some 100+ data sheets!
This is a 22 Meg resistor!
We did outsource a lot of production. That's why we spent a half megabuck or so for our own automated assembly and inspection gear. Our batches are too small to make a contract assembler care very much.
But the sales rep for the equipment also runs a winery in Murphys
and every equipment equipment order comes with some really good wine. The guy and his wife served wine at our last company BBQ, for free. Kept everybody's glasses full. I didn't think I liked Viognier, but he snuck a refill into my glass, and I declared it to be really good before I figured out what he'd done.
For trimming, you want the resistance to be a bit lower than the spec, so you can trim by removing material.
Sounds like they're just saving a small amount of material in the sputtering target.
Cheers
Phil Hobbs
That's a nice resistor, what's the TC spec? 25 ppm?
George H.
We have a couple of CMs that do our prototype builds but that may be larger than your production runs (usually ~25 boards). One of the CMs just opened a "local" line so I can deliver parts myself.
One of our CMs ships chocolate or popcorn with each order. The other took me out for a great Italian lunch (dinner, really).
I just tell the FAEs what specs I need and what I want to pay. They come back with what they have. ...and I get a few lunches out of it, in the mean time. ;-)
Seriously, there are so damned many opamps it's almost impossible to sift through them all, particularly since the listed prices are bogus.
Sure. FAEs have families who like to eat, though.
I find the Asian semi manufacturers to be difficult to work with, with the possible exception of Rohm. They do some of the dumbest things, too.
Yes.
I like the dry whites. Tasty.
Will do. I wonder how that wine made it to Occupied TN. They can't make much of it.
Let's hope that he keeps his solder paste away from his grapes.
Have something to add? Share your thoughts — no account required.
Ask the community — no account required