When choosing the operating temperature range of a capacitor, the first thing to consider is environmental factors. If the maximum ambient temperature of your product is 100 ℃, then capacitors with a rated temperature of only 85 ℃ will definitely not work. Similarly, if the minimum ambient temperature is -30 ℃, then you cannot use the temperature of a -20 ℃ capacitor.
So, what temperature range of capacitors should be selected reasonably? For example, if a capacitor operates at very high ripple currents, it will generate internal heating, which will cause the temperature of the capacitor to continue to rise and exceed the ambient temperature. Therefore, we need to consider capacitors with more operating temperature margin.
Generally speaking, capacitors used after rectifier bridges will have significant ripple currents. At this point, considering the ESR of the capacitor, the internal heating of the capacitor will be more severe, and on the one hand, a larger rated temperature range needs to be reserved for the capacitor.
On the other hand, when conducting temperature rise tests, we need to pay attention to the temperature of the capacitor. For example, the maximum ambient temperature for the product to be installed is 60 ℃. Do not only select 60 ℃, but also choose 105 capacitors. According to the first version of the temperature rise test data, the rated temperature range of the capacitors needs to be reduced or continued to increase.
In summary, when selecting the rated temperature of capacitors, we cannot simply leave a large margin for all capacitors. We should pay attention to the self heating of capacitors (the influence of ripple current) and determine a reasonable temperature rise range through temperature rise tests. For some filters or decoupling capacitors with small ripple currents, a derating of 80% or 70% can be chosen.
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