Why is the tantalum capacitor derated?

The optimum conditions for use of tantalum capacitors are -55-+125 degrees, and the rated voltage can be applied to test within 85 degrees. It is said that such conditions have shown that the temperature characteristics of tantalum capacitors are very good, but one thing that is often overlooked is that the test is carried out under a protective resistance of 1000 ohms. At the moment when the product is energized, the surges in the voltage and current in the circuit are very small. The excessively large instantaneous current is suppressed by the series resistance, so the change causes 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, the circuit will generate very high voltage at the moment of switching. Surge voltage and current change, therefore, in such circuits, tantalum capacitors will withstand voltages and high current surges exceeding the rated value at the moment of switching and breakdown failure. Therefore, tantalum capacitors used in such circuits After a lot of experiments, it is proved that if you want to ensure its sufficient reliability, it must be greatly derated, so that the sum of the surge voltage and the reverse voltage applied to the product in an instant cannot exceed the rated value. Tantalum capacitors used in such low-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 the harsh conditions of use of tantalum capacitors in such circuits, so the use of high voltages often leads to breakdown, and therefore, breakdown On the one hand, users cannot achieve a sheet product with higher withstand voltage capability under conditions where the volume and capacity are strictly limited.

The reason why the tantalum capacitor has such a harsh condition in the specific use is actually a dangerous failure mode of the tantalum capacitor; when the leakage current is too large, the withstand voltage of the product will rapidly decrease, and the breakdown will occur soon. Instantly, it can cause rapid collapse of the dielectric layer and cause combustion or explosion. Its defects cause the tantalum capacitor to exhibit very fragile characteristics in circuits with large inrush currents; surge resistance is among all capacitors. the worst.