colin wrote:

> "Jon Elson" <jmelson@artsci.wustl.edu> wrote in message
> news:45B7C3B6.5040909@artsci.wustl.edu...
> > colin wrote:
> > 
> > > "Jon Elson" <elson@pico-systems.com> wrote in message
> > > news:KNednYBbqKlBZSnYnZ2dnUVZ_vipnZ2d@giganews.com...
> > > 
> > > 
> > > > This is a real problem.  I haven't come up with any way to build
> > > > a good output filter for traditional PWM schemes like synchronous
> > > > antiphase, in which either the high-side or low-side transistor
> > > > are always on. I have a DC motor drive that uses sign-magnitude
> > > > 
> > > > 
> > > instead, and it works MUCH better.
> > > 
> > > 
> > > 
> > > Thanks, Im not familiar with those terms, but all my 3 outputs are
> > > always switching,
> > > thus at idle each is at 50% pwm.
> > > 

<Big Snip>

> yes I had considered that if I couldnt find what I wanted.
> also gate drive transformers driven from a HF chopped signal and
> rectified, as some mcu have PWM outputs wich can do this directly.
> 
> thanks for all the help and ideas, its clearer now.
> 
> Colin =^.^=

Please do not shoot the messenger, but i do not think that hobby 3-phase
motor controllers do not do any PWM at all.   Except at stop, to prevent
burning the motor up.  You can get one at any RC hobby shop, or on the
Internet.

I think that running the waveforms look like this:

A.     |-----_      |-----_      |-----_      |-----_
              _____-       _____-       _____-

B.     ---_      |-----_      |-----_      |-----_   
           _____-       _____-       _____-       ___

C.     -_      |-----_      |-----_      |-----_      
         _____-       _____-       _____-       _____


This is intended to represent "square waves" with a little dead time.

-- 
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller