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From: dbell@cup.portal.com (David J Bell)
Newsgroups: sci.electronics
Subject: Re: Thermoelectric coolers - how do they work - in English plea
Message-ID: <34081@cup.portal.com>
Date: 20 Sep 90 01:54:38 GMT
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Simply, the Peltier effect gives a correlation between thermoelectric
generation and electrical *pumping* of heat. Consider it analogous to
the way a DC motor can be used as a generator: with a Peltier device
(usually a P-N semiconductor junction, but I believe any two dissimilar
conductors), if you heat one junction (remember, there are always
effectively *two* junctions, but one may be made with copper wires
between the active materials), it will produce a current, just like
any thermocouple. If you drive a current into the device, though,
one junction will get hot, and the other will get cold. Reverse the
polarity of the driving current, and the hot and cold ends switch, too.

So: to cool a diode laser, bond the laser die to one junction of a
Peltier device, and bond the other junction to a heat sink or radiator.
Add current and you have instant cool. If you need more temperature
difference between "ends", stack the element with the laser attached
onto a few others (in a layer), and stack themin turn on a number
of *others* in a larger layer, on the heat sink; basically, build
a pyramid, with the coldest end at the tip, the hottest at the base.
You need the extra devices in each successive layer because they are
definately *not* 100% efficient - they produce waste heat as well as
pumping heat, just like a refrigerator...

Dave            dbell@cup.portal.com