The full name of tantalum capacitor is tantalum electrolytic capacitor, which is also a kind of electrolytic capacitor. For polar tantalum capacitors, reverse connection will cause the failure of tantalum capacitors (related to the voltage resistance of tantalum capacitors, such as 25V tantalum capacitors in 5V systems Reverse connection does not necessarily fail immediately, but in a 25V or 16V system, the reverse connection will soon fail), ranging from burning to smoke, and from fire to flame. Therefore, it is very important to distinguish the polarity of the tantalum capacitor when using it: on the chip tantalum capacitor, the positive electrode is marked with a dark colored strip or beveled edge; the long leg of the tantalum capacitor lead of the insert is the positive electrode.
Tantalum capacitors have the following characteristics:
1. Since there is no electrolyte inside the tantalum capacitor, it is very suitable for working at high temperature, that is, the working temperature range is wide, the forms are diverse, and the volume efficiency is excellent.
2. In the working process of tantalum capacitors, it has the performance of automatically repairing or isolating the defects in the oxide film, so that the oxide film medium can be strengthened at any time and its proper insulation capacity can be restored without continuous cumulative damage. This unique self-healing performance guarantees its advantages of long life and reliability. Due to the self-recovery ability of tantalum capacitors, tantalum capacitors do not necessarily fail permanently when working in occasions with large transient currents. Sometimes during board commissioning, you will find that the board suddenly powers off inexplicably, and it can work normally after being re-powered after a while. It may be caused by the temporary failure of the tantalum capacitor.
3. The ESL value is small and the high frequency filtering characteristics are good.
4. In use, the product working environment and its heating temperature should be considered, and measures such as derating should be taken. Generally, the working voltage of the tantalum capacitor should be derated by more than 50% relative to the rated voltage. One of the following three scenarios is encountered. The rated voltage of the capacitor needs to be derated by more than 70%: the load is strongly inductive, the series resistance is small, and the transient current is large. The reason is that an inductive load or a small series resistance will cause a large transient current, causing the metal dielectric of the tantalum capacitor to be broken down. At the same time, it is necessary to pay attention to the design, and try to avoid the use of tantalum capacitors in the power supply filter circuit involving hot swap.
5. The working medium of the tantalum capacitor is an extremely thin tantalum pentoxide film formed on the surface of the tantalum metal. This layer of oxide film dielectric is combined with one end of the capacitor to form a whole, and cannot exist alone. Therefore, it has a very high working electric field strength per unit volume, and has a particularly large electric capacity, that is, a very high specific capacity, so it is particularly suitable for miniaturization.
6. The price of tantalum capacitor is higher, the capacity is smaller, the voltage resistance and current capacity are weaker (the larger the capacitor capacity, the more stored charge, the more charge, the higher the voltage required).
Generally speaking, the larger the tantalum capacitor, the smaller the ESR value. According to the equivalent circuit of the capacitor, ESR is equivalent to the series resistance of the capacitor device. The smaller the series resistance, the easier it is to cause the capacitor to fail. Therefore, it is necessary to pay attention to the application. For large-capacity tantalum capacitors, voltage derating is more required. In terms of cost, the price of tantalum capacitors is proportional to the product of the capacitance value and the rated voltage. When using a tantalum capacitor with a large capacitance value, it is necessary to increase the ratio of voltage derating, which will cause the cost to rise. Therefore, in the design, several tantalum capacitors with small capacitances can be connected in parallel to provide the same capacity as the tantalum capacitors with large capacitances. This is not only beneficial to the reliability of the design, but also to cost reduction.
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