Re: Value of Zener diodes

Grant:

The value of the zener must be higher than the peak output of your
transformer. I use about 10% - 20% higher. So, for example with a
24V transformer you'd get a peak output of 1.414 * 24V = 33.96V peak,
use a 39 or 42 Volt zener. The purpose of the zener is not to
regulate the power supply, but to absorb the excess energy returned
by the stepper motor.

Tony


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "grantfair2001"
<grant.fair@s...> wrote:

> Jon-
>
> How is the value of the zener established? I am using a current
> limiting power supply which operates at up to about 30 volts.
>
> Grant
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...>

wrote:

> > A unipolar drive has
> > several ways to deal with the voltage and current in the
> "turned-off" half
> > of the winding. The most common scheme is to have a freewheel

diode

> > that sends the current back into the power supply. This

effectively

> shorts
> > out the winding, and a shorted winding changes current only

slowly.

> > To get faster charging of the winding, resistors, or Zener diodes

can be

> > put in series, so a large voltage is developed across the winding,
> thereby
> > draining the magnetic field quickly. This, however, burns

substantial

> > energy as heat every time the driver makes a step.
> >
> > Jon