I'm attempting to make a system where I mirror a single voltage across multiple diodes and get roughly the same current in each. I've had excellent luck using the PHPT610035 PNPs, but if I want to mirror the current more than one time, I need to daisy chain these devices. Does anyone know if there are matched BJT or diodes that come three or more to a pack?
Posted Mar 10, 2018, 12:02 AM UTC
Perhaps MMPQ2222?
Ooh, good find! They don't spec any matching characteristics on the datasheet, though. So I wonder if sometimes you might get multiple dies from different runs.
I highly doubt that they are putting more than one die in the device.
But if you absolutely must know the transistors are matched:
https://www.mouser.com/ds/2/407/300data-180007.pdf
https://www.mouser.com/ds/2/609/MAT14-879573.pdf
The list goes on. The key words you are looking for are "matched array".
They're... They're beautiful.
I really don't know, but I would imagine that transistors next to each other on the reel were made in the same batch, and are likely to be pretty decently matched.
So maybe try, and just thermally bond them if they're going to be dissipating enough to self-heat. ?
?
i don't know, just an idea.
Yeah, but I used to work in ic design, and even the variation from one end of the Silicon wafer to the other is too much. Just guaranteeing that they are from the same batch gives you some measure of stability, and would probably work in most cases, but I'm aiming for tighter matching than that.
Thanks, though.
geez i had no idea. i figured the doping would match, any contaminants would be similar, and a similar tolerance W & L would be achieved?
what, exactly, changes from one edge of the wafer to the other?
The doping itself can actually vary from one side to the other, and contaminants and silicon structure are more likely to have subtle differences the farther apart you go on the surface. The tiniest misalignment of masks can cause apertures to be ever so slightly different, meaning one PN Junction gets made slightly deeper than the other, or one Gap is slightly narrower than another. That's the idea.
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Better solution: add small resistors in series with the emitter; then, matching doesn't matter so much.