🚀 go-pugleaf

gude@uniwa.uwa.edu.au (David J W Emrich) writes:

(about driving a stepper; winding ct to +V, sides to NPN's)
>reversed! The only thing to watch is that you put swamping diodes
>across the NPN transistors, so that back- emf from the coils doesn't
>shoot them!

But you should return the diodes to +2V, at least (and have
transistors that will stand off that voltage).  You want to
change direction of the current as fast as you can for fast
stepping, and a diode directly across 1/2 the winding will
keep current going in that winding for some time.  Also, if
there is transformer action between the two halves of the
winding, the newly-on transistor will be trying to drive
current into that diode, if it's returned to +V, and make 
the transistor's collector current higher than you planned 
(possibly by quite a bit!).