Re: Microstepping - Constant freq. vs constant off-time.

Hi,

Constant off-time:

+ Very simple, effective circuit.
+ Stable operation.
- Frequency varies with current.
- Annoying hissing and squealing because of phase-locking.
- Asymmetrical current slopes cause "tailing" distortion.

Constant frequency:

+ Silent; no hissing, squealing, etc.
+ Lower distortion, no current "tailing".
+ Electrical noise is synchronous and is easily rejected.
- More complex circuit.
- Overconstrained current loop; requires feed-forward compensation.

Most people don't like the audible noise, so my choice is constant
frequency. I'm also a fanatic about accuracy, so again, same choice.
Finally, it's a lot of fun to design "difficult" circuits.

Mariss


--- In CAD_CAM_EDM_DRO@y..., "Henrik Olsson" <henrik-olsson@t...>
wrote:

> Hi all,
> Here's a question for the electronic guys.
> Looking at some datsheets for stepper controller IC's i read that

it's

> better to use a constant off-time chopper instead of a constant

frequency

> chopper in a microstepping drive.
> What is the difference and what difference does it make? Would it

be a bad

> idea to use the L6506 in a microstepping circuit just because it's a
> constant
> frequency controller?
>
> Thanks!
> /Henrik Olsson. Sweden.
>
> PS. For those of you interested in stepper driving circuits I can

recomend

> the ST app-notes and datasheet site at:

http://www.st.com/stonline/books/