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Why are tantalum capacitors required to derate the voltage?

Date: 2022-10-24

The suitable operating conditions of tantalum capacitors are -55-+125 degrees, and the rated voltage can be applied within 85 degrees for testing. It is said that such conditions have shown that the temperature characteristics of tantalum capacitors are very good, but one thing is often overlooked, that is, under this condition, the test is carried out with a protective resistance of 1000 ohms. At the moment when the product is energized, the voltage and current in the circuit have very small surge changes, and the excessive instantaneous current is suppressed by the series resistance. Therefore, the change has an impact on the tantalum capacitor.

In actual use, tantalum capacitors are often used in power circuits without any resistance protection for filtering or charging and discharging. If such circuits use an external power supply, at the moment of switching, the circuit will generate a very high voltage. Surge voltage and current changes, therefore, when used in such circuits, tantalum capacitors will be subjected to voltage and large current surges exceeding the rated value at the moment of switching and breakdown. Therefore, tantalum capacitors used in such circuits , After a lot of experiments, it has been proved that if you want to ensure its sufficient reliability, it must be greatly derated to ensure that the sum of the surge voltage and reverse voltage instantly applied to the product cannot exceed the rated value. Tantalum capacitors in impedance circuits are therefore required to be derated to 1/3 of the rated value to ensure reliability.

Such requirements have brought a lot of inconvenience to actual users; on the one hand, many users do not know such harsh conditions of use of tantalum capacitors in such circuits, so the use voltage is too high, which often causes breakdown, and on the other hand, On the one hand, users cannot achieve chip products with higher withstand voltage capabilities under the condition that the volume and capacitance are strictly limited.

The reason for such harsh conditions in the specific use of tantalum capacitors is actually a dangerous failure mode of tantalum capacitors; when the leakage current of tantalum capacitors is too large, the withstand voltage of the product will decrease rapidly, followed by breakdown. It can cause the rapid collapse of the dielectric layer and the phenomenon of burning or explosion in an instant. This defect causes the tantalum capacitor to be very fragile in circuits with large surge currents; the surge resistance is the highest among all capacitors.

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