For motor control,  the ideal is up above 15KHz simple because the noise
(whine is more like it) can drive people to do unatural acts.)  But I've
just done some PWM on a 10A 48V solenoid where I drive it at 100% until
the current approaches my cuttoff point and then I bring the current
down to about 5%.  That pulls the solenoid in really quickly with
maximum torque but holds it at a much lower current using far less
power.

John


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of michael brown
> Sent: Wednesday, March 20, 2002 12:25 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE] PWM frequency
>
>
> > The best PWM frequency is usually the highest frequency you
> can afford
> > when you consider the efficiency of any chokes or coils you use the
> > PWM voltage on (they have a maximum efficiency rated
> frequency). Also
> > because high frequency requires lower value filter capacitors and
> > inductors for the same smoothing, and the design should be cheaper
> > like this.
>
> Peter,
>
> I don't disagree with you, but I have a question.  Don't
> FET's generate most of their internal heating during the
> transition phase (turning off or turning on, just not quite
> all the way on or off yet).  If so, wouldn't this make a case
> for a lower PWM frequency?
>
> michael brown
>
> --
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>
>
>

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