Re: Stepper Voltage and Current question

Here is something I just came up with. I'll have to do more reading
on the data sheet but if anyone is interested check it out.
www.allegromicro.com SLA7026 High current PWM Unipolar stepper motor
controller/driver. Looks like it does everything and I can get them
for $8.23 a piece. If anyone cares to comment I'd appreciate your
thoughts.

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> starcast82 wrote:
>
> > I plan on limiting the current through transistors not resistors.
> > This way when I pull 25 volts or 50 volts it will be limited to 2
> > amps to the motor. I may also use FET's to keep the heat down.
>
> If you do this linear, FETS or bipolar transistors will dissipate
the same
> heat as a resistor. (They will allow a faster current rise,
however.)
> So, don't think that without switching technology, that magically
> putting FETs in the circuit will make the heat go away.
> (25 -3 V) * 2 A = 66 W for each phase of each motor.
>
> > I just
> > need to know if each winding is rated for 2 amps or is it divided
> > between the 4. I was just curious performance wise how much
voltage I
> > needed. I may add a chopper cicuit by adding a 555 timer to the
> > tranistor circuit but am working on the basic circuit first and
try
> > to make sure what I need voltage and current wise.
>
> A 555 timer is not a good choice for a chopper drive. You need to
> allow current to rise to the setpoint, and then turn off the high-
side
> transistor and allow the current to circulate until it falls below
a setpoint.
> You can do it with other components, but eventually the 555 is just
the
> wrong part (I think).
>
> > Gecko drives are nice but at $130 a piece I figure I can design my
> > own a lot cheaper since this will be my first table and can always
> > upgrade if the need be.
>
> Unless you are an electrical engineer with some experience in power
> circuits, I'm afraid you will smoke a lot more than $130 x 3 before
you
> get it right.
>
> Jon