Re: Stepper controllers

"Ian W. Wright" wrote:

> From: "Ian W. Wright" <Ian@...>
>
> Thansk Dave,
>
> Do you mean that your diodes are in series with the wires to the motors?
> The circuit I am using has diodes from each motor wire to ground but it
> would seem safer to put some in the motor wires as well. The only worry
> I would have is the breakdown voltage of the diodes - as I understand
> it, the voltage spikes produced by such motors can be many times the
> operating voltage so I'm not sure how I should choose the diodes working
> voltage to be on the safe side.

No, this is all wrong. You don't want to 'block voltage', you want to
recirculate current. The inductance of the motor causes voltages to be
produced when you abruptly try to stop the current. Generally, in the
case of the resistor-fed unipolar stepper driver, you have a diode's anode
at each end of the motor winding, (where the transistor also is connected)
and the cathodes connect back to the motor's center tap. You can connect
a small value resistor in series with the diode to allow the current in the
motor winding to collapse faster.

In your scheme, you need not worry about the diode's blocking capacity,
you'd better worry about the motors' voltage capability. You could
easily develop several hundred volts of flyback when the current is
abruptly stopped, and it could arc over inside the motor.

Jon