Paul B said
+AD4-  I'm not sure what you're saying here?  Wouldn't you want to tie it
to
+AD4-a 2xVcc rail like you just described?


Tying to 2Vcc+- would be SAFEST.
What I am saying is that if you can tolerate the ringing voltage it has
least effect on operation if you leave the diodes open (or with a very
light load).

Operate the circuit  - look at the diode common point on an oscilloscope -
decide whether the result is tolerable for your driver. Depending on your
switching waveforms, relative on and off times and the amount of leakage
inductance you may see very little ringing here as the other end of the
same winding is clamped to ground. This is what produces the 2:1
transformer action but also limits the voltage excursion. Be sure that what
you do is OK in all circuit configurations - eg do you ever suddenly turn
it off rather than stepping? (yes, you do :-)).



RM


-----Original Message-----

+AD4-Russell McMahon wrote:
+AD4-
+AD4APg- In one design I drive a small unipolar stepper similar to this one
+AD4APg- with a ULN2803 darlington driver with built in diodes and I leave
the
+AD4APg- common diode point open. In this case the driver is happy. YMMV
:-).
+AD4-