> When the voltage across the current sensing resistors reaches the
> Vref level the outputs are then driven to either a high or low as set
> by the Control line.  The idea is that the power to the stepper motor
> windings is either cut off and grounded or set to the supply potential
> which can result in less current drain and allow for smaller sensing
> resistors.

Andy, thanks for paraphrasing what chopping is about. I'm getting parts
from discarded Nokia RF tuners. Basically the stepper moves a copper
disc into a cavity, via a screw thread

Anyhoo, I notice on these boards that Vref seems to be mid-supply
(DMM resistance reading with no power), and the sense resistors are
10 ohms. With V+ of only 5V for 10V motors, even with my limited
knowledge it seemed the drive would be quite weak. My "junk"
supplier called around today with another load and told me that it
wasn't unknown for these tuners to stick and you'd have to give them
a wallop

Just a little anecdote I thought I'd pass on. It's one of those handy
insights to help understand how the circuit does what it does. Or
occassionally doesn't



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