New-Tech Europe Magazine | May 2018

Figure 1. Internal structure of a generic Peltier element

Figure 2. The Peltier element, aluminum block and heat sink are assembled to create the cooling system

Module and Controller Selection A complete thermoelectric cooling system comprises the Peltier element and heat sink assembly, temperature sensors to monitor the hot and cold plates and a controller unit to ensure the correct current is supplied to maintain the desired temperature difference across the module. The controller and Peltier module are chosen to ensure the heat from the cooled component combined with the joule-heating effect of the

the substrate on the opposite side. Therefore, the surface where energy is absorbed becomes cold and the opposite surface, where the energy is released, becomes hot. Constructing a Cooling Unit To create a practical thermoelectric cooling unit, the Peltier module is built into a system that usually comprises a metal block of high thermal conductivity, such as an aluminum alloy, and a finned heat sink (figure 2). The metal block is used to attach the device to be cooled – such as the laser diode or image sensor – to the cold side of the cooling element. The thickness of the block is selected to maintain flatness and so ensure consistent thermal connection with the cold plate of the Peltier element, noting that excessive thickness will introduce unwanted thermal inertia. The heat sink is attached to the opposite side, or hot plate, of the Peltier element, to dissipate the extracted heat into the ambient environment. A thin layer of thermal grease, or other thermal interface material (TIM), is applied to each surface.

supplied current can be dissipated without exceeding the maximum thermal capacity (Qmax) or maximum temperature difference (ΔTmax) indicated in the Peltier module datasheet. The maximum temperature difference and maximum current should also be considered, to ensure the chosen Peltier module can maintain the desired temperature difference when operating at a suitable current. This should typically be less than 70% of the maximum rated current, to ensure that joule heating remains within manageable limits and

Figure 3. Calculation of setting using datasheet function diagrams

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