> The one I bought came with a warning NOT to use
> PWM under 2kHz, apparently that produces too much
> thermal stress. Very low frequencies (like you
> mentioned) may be ok and are used in some cheap
> car fridges, but a slowly ramping PWM at higher
> than 2kHz will give the longest life, possibly
> run from a nicely filtered buck converter even
> better still always providing DC to the device.

So you need a 'hybrid' approach, with the real PWM at a very low
frequency, and the edges of that PWM smoothed by a high frequency PWM?
Does not sound to difficult, especially because the ramp-up time of the
higher frequency PWM is not critical.

Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products

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