Hi all,
I'm considering binning several thousand jfets with a view to selling matched sets. Given the scale of the task, some thought around best practice seemed wise.
At one end I could buy a curve tracer and individually mark every part, in a climate controlled environment... at the other end, I could sit at the kitchen table, measure Idss and bin in particular ranges, say to 0.1 mA.
What would be the 'pragmatic best practice' for this sort of task? In a home environment...
Cheers,
A.
I'm considering binning several thousand jfets with a view to selling matched sets. Given the scale of the task, some thought around best practice seemed wise.
At one end I could buy a curve tracer and individually mark every part, in a climate controlled environment... at the other end, I could sit at the kitchen table, measure Idss and bin in particular ranges, say to 0.1 mA.
What would be the 'pragmatic best practice' for this sort of task? In a home environment...
Cheers,
A.
according to Pa, second one is pragmatic best practice
and I know some of Greedy Boyz will tell you different
and I know some of Greedy Boyz will tell you different
Cheers ZM, in the back of my mind I'm wondering if I test at a notional current, or build a jig that makes it easy to do say Vp and idss and then bin in a 2 dimensional way.
I'd hate to get to the end of it all and have someone suggest a minor time addition that would make a big difference to saleability.:ROFL:
I'd hate to get to the end of it all and have someone suggest a minor time addition that would make a big difference to saleability.:ROFL:
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Hahahaha. Indeed 🙂
Idss matching has been good enough for me, and certainly is fastest in the end.
I suspect after 2k or 3k of them I'll be heartily sick of any additional steps...
I'm recently unemployed and I thought this might be a way to make a bit of pocket money whilst interviewing. Going to the beach also seems pretty compelling... 🙂
Idss matching has been good enough for me, and certainly is fastest in the end.
I suspect after 2k or 3k of them I'll be heartily sick of any additional steps...
I'm recently unemployed and I thought this might be a way to make a bit of pocket money whilst interviewing. Going to the beach also seems pretty compelling... 🙂
with 9V battery , you can do matching on da beach .......
though , better in shade ...... some porch, cold beer , biiig table
though , better in shade ...... some porch, cold beer , biiig table
As soon as you have measured ten of them you will need some kind of software to tell you which of them you'll need to pack together.
with 9V battery , you can do matching on da beach .......
though , better in shade ...... some porch, cold beer , biiig table
Hahahahha. Sounds excellent, although I suspect I'd come back with a tan, empty beers and a smile, and not a lot else.
Not really. I'd thought to bin then by some arbitrary range, say 0.1mA and anything in that bin is within 0.1mA of each other. After 2K of them if there's some outliers, then so be it.
Of course I could bin by the 0.01, and have a truly enormous collection of bins (for 4mA variance that would be 400 bins vs 40 for 0.1), but then I'd have to decide on the time/additional price charged math.
Bear in mind also usually NP might only match to 1mA for signal jFets, so 0.1mA matching is 10 times better than what NP normally does.
Good luck with measuring and grouping thousands - what device's are you looking at?
Good luck with measuring and grouping thousands - what device's are you looking at?
The usual suspects. I've a sample set of k170's to work through the kinks and verify the parts and how long the process takes before I get too carried away.
After all, if it only nets me below minimum wage, I could just go flip burgers for fun for a while instead. :Clown:
After all, if it only nets me below minimum wage, I could just go flip burgers for fun for a while instead. :Clown:
Pass DIY Addict
Joined 2000
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My experience with matching shows that just a few seconds (10-15s) is enough to get good data and make good matches. Just be consistent with your timing as self-heating plays a role.
Test them with a 12v wall wart or power supply so voltage stays consistent, with a DVM in series. Let them heat up until the measurement stabilizes to somewhat simulate in circuit conditions. May take a minute or so but results are pretty accurate. They will change over this period and some more than others. What you measure initially and after they warm up can be significant. Consistent room temp is important too.
TJ
TJ
I find that matching Idss to .5ma-1ma is adequate in most cases. Better Idss matching might not give closer Vgs match at running current, which is the most important for lowest DC offset.
BTW, perhaps I should share a couple observations about testing large
quantities.
Obviously test conditions should be relatively constant. Room temperature
is a factor also.
My test rig settles in about a second, and I take the voltage then. The
value will drift as the seconds go by, but it works if you are consistent.
Obviously high Idss values will heat more, so at values above 15 mA
or so consider using the Vp pinch-off test instead.
If you are doing .1mA resolution, it's best to sort them into 1 mA bins
and then retest those bins at .1mA. Gets the human and other error
factor way down. Once you are confronted with accidentally tossing
a fet into the wrong bin which has a couple hundred parts, you will see
that it's worth the extra effort.
quantities.
Obviously test conditions should be relatively constant. Room temperature
is a factor also.
My test rig settles in about a second, and I take the voltage then. The
value will drift as the seconds go by, but it works if you are consistent.
Obviously high Idss values will heat more, so at values above 15 mA
or so consider using the Vp pinch-off test instead.
If you are doing .1mA resolution, it's best to sort them into 1 mA bins
and then retest those bins at .1mA. Gets the human and other error
factor way down. Once you are confronted with accidentally tossing
a fet into the wrong bin which has a couple hundred parts, you will see
that it's worth the extra effort.
I have been using this simple test rig, Fig 9. All on breadboard, with connectors for fresh batteries and sockets for transistors. And two multimeters.
Biasing JFETS
Biasing JFETS