Key words
TEC
TEC Cooler
Article contents
The selection of thermoelectric refrigerator is an iterative process. In addition to the basic size information, a typical TEC specification contains the following basic information:
Qcmax: The amount of heat that a thermoelectric cooler can transfer when the temperature difference between hot and cold surfaces is 0℃.
Imax: The maximum current allowed through the thermoelectric cooler;
Vmax: the voltage at both ends of the thermoelectric cooler when it passes the maximum current;
DTmax: The maximum temperature difference reached between the two ends of the thermoelectric cooler when the maximum current is passed through the thermoelectric cooler and, at the same time, the heat loaded by the thermoelectric cooler is zero.
COP: the coefficientof complex performance, which is the ratio of the heat value of cooling to the input energy Qc/(V*I);
Th: thermoelectric cooler hot end temperature;
RAC: Resistance of thermoelectric cooler
The following figure shows the basic parameter table of Laird TEC:
For TEC, when the operating temperature is different, the key parameters mentioned above will also be different due to the change of electrical performance. In this example, the performance parameter is set to 50℃ at the hot end. Suppose the demand scenario is: the power consumption of the heating chip is 20W, and the temperature is required to be controlled at 26℃. Based on this, the working point (working current and working voltage) of the TEC is calculated. When the chip temperature is controlled at 26℃, the temperature rise is required to be 24℃. According to the refrigerating capacity, current and temperature difference chart in the specification, the working current should be 4A:
The current of 4A here refers to the current when TEC works stably. When starting, the working current is slightly higher. In some TEC specifications, voltage, current and temperature difference diagrams are also provided. In this case, the corresponding voltage line can be found in this diagram, and the temperature difference is zero (in the initial state, the temperature difference between hot and cold surfaces is zero), and the initial current value can be obtained retrospectively. If this diagram is not provided in the specification, it is usually set at ~1.2 times the steady-state current value. According to the current, voltage, temperature difference chart, check the working voltage is 4.5V. According to the working voltage and current, in order to achieve the current heat transfer and maintain the required temperature difference, the required input power is Pin = I * V = 4A * 4.5V = 18W. The comprehensive efficiency coefficient of TEC was COP = 20W/18W= 1.11.
From this figure, not only the COP value can be checked, but also the highest efficiency point of TEC working under this operating temperature difference and voltage can be determined. As this figure shows, the COP value is clearly not optimal. This TEC achieves 20W power consumption. When the ambient temperature is 24℃ and the chip junction temperature is 26℃, the additional power input is 18W. In order to achieve this effect, the following two pieces of information should be satisfied:
The setting of the circuit should be able to support the current demand of TEC;
The heat sink assembled on the hot surface of TEC can steadily lose 38W heat (the calorific value of chip is 20W+ the input power of TEC is 18W) under the premise of maintaining the temperature of the hot surface at 50℃.
Therefore, it is not difficult to see that the design and selection of TEC requires the matching design of circuit and radiator. Moreover, the heat load of the radiator is equal to the sum of the heat of the chip and the input power of the TEC. When the COP value of TEC is not high, TEC needs higher input power in order to transfer the specific power of the chip in time, which not only reduces the energy efficiency of the design scheme, but also increases the heat load of the radiator, bringing difficulties to the final heat transfer. Therefore, the selection of TEC is an iterative process. Before the final selection of TEC, the above methods should be used to compare the comprehensive efficiency values of multiple TEC, and the thermoelectric cooler with the highest energy efficiency ratio should be selected to achieve the most energy saving scheme and the minimum design requirements of external cooling system.
Therefore, it is not difficult to see that the design and selection of TEC requires the matching design of circuit and radiator. Moreover, the heat load of the radiator is equal to the sum of the heat of the chip and the input power of the TEC. When the COP value of TEC is not high, TEC needs higher input power in order to transfer the specific power of the chip in time, which not only reduces the energy efficiency of the design scheme, but also increases the heat load of the radiator, bringing difficulties to the final heat transfer. Therefore, the selection of TEC is an iterative process. Before the final selection of TEC, the above methods should be used to compare the comprehensive efficiency values of multiple TEC, and the thermoelectric cooler with the highest energy efficiency ratio should be selected to achieve the most energy saving scheme and the minimum design requirements of external cooling system.
