Re: current set resistor

Peter,

Good evening! The current set resistor forms the bottom half of a
voltage divider. The top half is a 47.5K resistor that goes to a
16.5V reference. The motor current is proportional to the voltage
formed by this voltage divider. You would indeed use no resistor at
all if 7A per phase is required. A 1/4W 5% resistor is OK.

Mariss

--- In CAD_CAM_EDM_DRO@y..., cadcamcenter@y... wrote:
> Hi,
>
> In the unipolar drives, the current limiting resitor is used to
limit
> the current to the motor when back emf is zero or very low. Knowing
> this it is easy for one to calculate what resistor to use given the
> coil resistance.
>
> I hope to understand the use of the current set resistor for the
> gecko stepper drive. Is the current set resistor put there
to "sense"
> when current need to be chopped off or something? Understanding it
> will make one more confident in calculating a suitable resistor to
be
> used with a particular motor, rather than just plugging specs into
a
> given formula without understanding the formula
>
> R = (47,500 * I)/(7 - I)
>
> It would help to know where the 47,500 and the 7 came from. What
> should one do, for example, if the motor rated current is 7 amp (R
=
> infinity) keep the teminals 11 and 12 open?
>
> Thanks
>
> Peter