Testing H7864 (MicroVAX II) PSU With No Load

tony duell ard at p850ug1.demon.co.uk
Sun Nov 1 12:54:23 CST 2015

> 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. 


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