Re: [CAD_CAM_EDM_DRO] RE: Stepper questions

Phil Mattison wrote:

><snip>
>The most common technique is to place diodes to return the current to the
>power supply, but this basically leaves the coil short-circuited.
><snip>
>
>>From all I have read and all the schematics I have looked at, the porpose of
>the diodes is to protect the power supply from harmful reverse current cased
>by inductive kick-back as the field collapses. Shorting out the coil is
>precisely the objective. Otherwise the switching transistors can become
>reverse-biased and burn out.
>
>

Actually, it is to protect the power TRANSISTORS, not the supply. But,
if you put a
little resistance in series with it, the field will collapse faster. If
you used transistors
rated at several hundred volts, you could allow the field to collapse
very quickly with
larger value resistors, but the resistors would then dissipate a lot of
heat all the time,
whenever the chopping circuit turned the transistors off. That is why
most simple drives
just use the diode without any added resistance.

Jon