Is it standard that a TO-220 transistor package is, with the tab up, with the markings facing you, Base, Collector, Emitter? (for example, on the TIP31A)
I noticed the TO-92 2N3904 I have is (with the markings facing me) E B C, and a TO-92 2N2222 data sheet even shows C B E !!!
Michael
The TO-220 package is used for many devices not just transistors. The pinout is what the data sheet says it is. Always consult the data sheet if the leads are not marked.
Tom
So does this mean it is NOT standard that a TO-220 *transistor* package is BCE? (with the markings facing you)
Michael
You will find some that are not that way.
Tom
Thanks.
Michael
For pcb layout ? I like to make the central pin 0.1" ? Forward of the other two. When unheatsunk it also gives greater mechanical stability.
It gives greater pad clearance too.
Graham
BCE to me, then which way are you looking at it ? READ THE DATASHEET.
Grahan
Like FETS !
Graham
It is _common_ for a TO-220 transistor to be wired that way, but not universal.
The manufacturer will pin out the transistor in the way they think is best; usually this means connecting the collector to the tab for good heat dissipation, and to the center pin because that's what wants to connect to the tab (I don't know why center pin = tab; I assume it's for some sound mechanical reason).
For a while (and perhaps still) there were budget TO-220 RF transistors that put the emitter on the tab, to reduce the capacitance to ground from the collector.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html
It's the bulk of the die substrate.
Graham
OK, but why does the mounting tab have to go to the center pin? If it's all being stamped out of sheet anyway, why not have the mounting tab connected to the right pin, or the left?
I assume there's a good reason, because AFAIK the center pin = tab is just about universal.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html
I think it is all about physical stability of the base and emitter lead frames. If they are tucked into a notched corner of the collector frame, they are stronger than if they are just hung off the side of the collector frame, as the far corner lead would be with the base and emitter in the center and corner positions. Since they are held in place only with the epoxy cast, having metal around two sides of the end of the base and emitter lead gives added rigidity and strength. At least, after blowing a few up and seeing how they are made, this has been my assumption.
Perhaps Phil or someone who does investigation of explosive failure has some good photos of the exploded construction. A dental X-ray or two would be neat to see, also. I know that a common failure mode I have seen with the TO-126 (smaller than the TO-220 power tab, with the hole through the epoxy and no exposed metal tab) is the base or emitter lead frame breaking lose from the epoxy so the bond between the lead frame and the die breaks.
The TO-202, however seems to be fine.
But they do put the beveled (weaker) end of the epoxy over the collector pin, and have the full epoxy thickness over the emitter on the far corner. Still more rugged than the TO-126.
-- Regards, John Popelish
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