At 03:01 PM 2/5/2003 +0100, you wrote:
> > By the way, Peltier devices are badly suited to be driven via
> > PWM.
>
>IIRC Peltier devices are heat pumps? If so their action is inherently
>slow due to thermal inertia, so you can PWM at a *very* low frequency,
>like N seconds on each minute. Easy in software, and would probably
>avoid the inefficiency Olin mentions.

No, Olin is correct, the problem is I^2R heating in the device.
Consider the ratio of average current (determines heat pumped) to RMS
(determines heat loss). It is 1:1 for DC, whereas at 50% duty cycle
PWM it is 1:2.  You can, of course, *increase* the frequency and put a
relatively small gapped inductor in series with the Peltier device so that
the current it sees has low ripple- you don't *have* to use an inefficient
linear regulator.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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