AVR-Chat

This is absolutely true and is a point worth making.

Some loads work well directly driven by PWM. Heaters and
motors are good examples. Typically, these are devices with
a long mechanical time-constant compared to the PWM period.

When you can do this, it it typically more efficient
(power-wise). Fewer or no heat-sinks. Switching devices are
used instead of analog things where linearity may be an
issue. All of these create a cost benefit for PWM. 

All of that said, the cases where you can use PWM in this
way are limited. But, where you can, it really helps.

Jim

On Mon, 09 Jan 2006 23:59:34 -0500
 Robert Adsett <subscriptions@aeolusdevelopment.com> wrote:
> At 11:18 PM 1/8/06 +0530, Anurag Chugh wrote:
> >why only PWM?.. why not use an R2R ladder instead with
> precision resistors...
> >i know they would hog a whole PORT but arent they easier
> to implement ??
> >and they can do DC output values too... a simple opam in
> front (voltage 
> >follower) will boost current output too...
> 
> Not quite in the same line of thought but no one has
> mentioned the other 
> reason to prefer PWM over R2R in some situations and that
> is power.  Feed 
> the PWM into a power device rather than an RC filter and
> with a slowly 
> responding load like a heater tank or a motor the load
> itself acts as the 
> low pass filter and you avoid the losses that a linear
> solution would 
> entail.  At the cost of ending up with high frequency
> current transients of 
> course.
> 
> Robert
> 
> " 'Freedom' has no meaning of itself.  There are always
> restrictions,   be 
> they legal, genetic, or physical.  If you don't believe
> me, try to chew a 
> radio signal. "  -- Kelvin Throop, III
> http://www.aeolusdevelopment.com/
> 
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