> That said, it's possible that there may be an auxiliary linear regulator in > there. That's common > for additional outputs with modest current needs, especially in older > designs where the > switching circuitry takes a lot of individual components. A TO-3 can isn't > what I would expect > to see in a switching-only supply. In other words, that particular > transistor might be the pass > transistor of a linear regulator.
There are plenty of suitable chopper tramsistors in TO3 packages. The BU208 is the first one I think of (being this side of the Pond). I've just looked up the printset for the 11/730 PSU (mine will be on the bench soon I hope...). There are, as I said, 4 SMPSUs in there, 2 of them use choppers in TO220 packages, the other 2 use choppers in TO3 packages. -tony
