Re: Medium power transistor question

Windell Oskay

When we designed in the part, it was an active production part, easily found in distribution, and not remotely overkill.  Unfortunately (1) they have now been discontinued in the through-hole package, and (2) most of the comparable parts do not have the same pin order. 

The actually important spec– the reason that we were using this type — is the saturation voltage.  If the board needs to be able to run from 4.5 V (as do the Peggy 2 and Meggy Jr RGB), and the LED drivers drop a certain voltage, and you need to be able to drive blue or white LEDs that take up to 3.6 V to run, then there’s only about 0.5 V (or less…) available for the high-side driver to take up.  
So, your high-side driver needs to be able to handle roughly 25 LEDs * 25 mA = 625 mA (25 LEDs for a Peggy 2 row, or 24 LEDs for a Meggy Jr RGB row), and have low saturation voltage, hopefully spec at < 0.5 V at 1 A.  And, if you search for those two requirements (plus packaged in a through-hole package), you’ll find very few options.  One is the “big expensive brother” of the 2stx2220, the stx790A (also now discontinued).  Another is the BC640TA, which might be a good choice for you.