Re: Microstepping thru the Tulips

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
<mariss92705@...> wrote:

>
> I have thought a little about the relationships you mentioned over
> the years.:-) I'll just cover the step frequency vs. PWM frequency
> thing:
>
> I think you misunderstand how PWM works. Microstepping frequency and

PWM

> frequency are completely unrelated. This thought experiment may help
> to straighten it out:
>
> I think you agree that 400 Hz step rate on a full-step drive results
> in a 100Hz current waveform frequency. The full-step sequence repeats
> after 4 full steps after all. This modulates OK on a 20kHz PWM for a
> motor speed of 120RPM.
>
> A 250-microstep drive needs a 100kHz step pulse frequency to get a
> speed of 120RPM. The current waveform frequency is still the same and
> it still modulates OK.
>
> 100kHz is way above the PWM frequency but the PWM never sees it. It
> only sees the resulting 100Hz reference, the same as for the full-
> step drive. This also modulates OK on a 20kHz PWM.
>
> Mariss
>

It sounds like the chopping and PWM and microstepping are all
unrelated (isn't de-coupled a better word?), yet doing a very
choreographed dance.

In your post, you didn't describe chopping and it's part.

I have always thought chopping was a separate circuit from the pulse
rate and also the PWM.

Can you elaborate a little on the chopping ?

Dave