Re: TO-220 pinout standard?

mrdarrett@[EMAIL PROTECTED]
 wrote:
> 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

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

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