The capacitor medium cannot be absolutely non-conductive. The capacitor is applied with a DC voltage, the capacitor will have leakage current（LC).
- Electrolytic capacitor
The two poles of the electrolytic capacitor are made of a dense insulating film that is electrochemically formed with an insulating medium in the middle. There will be leakage current when voltage is applied. And because the insulating medium is electrochemically formed, the insulating film will continue to be repaired when the two poles of the capacitor are pressed, so the leakage current will continue to decrease. But if the voltage is not applied, the leakage current of the electrolytic capacitor will rise. This is the self-healing nature of electrolytic capacitors.
- Tantalum capacitor
The capacitor medium cannot be absolutely non-conductive. When the capacitor is applied with a DC voltage, the capacitor will have leakage current. If it is too large, the capacitor will be damaged by heat. Except for electrolytic capacitors, the leakage current of other capacitors is extremely small. Tantalum capacitor is also a kind of electrolytic capacitor, so the leakage current is relatively large. When the voltage is too high, the LC becomes very large. For capacitors of the same brand and series, when the capacity and withstand voltage are the same, the lower the ESR, the greater the LC. When the withstand voltage is the same, the greater the capacity, the greater the LC. When the capacity is the same, the higher the withstand voltage, the greater the LC.
- Ceramic capacitor
The ceramic chip capacitor MLCC should be highly insulated under normal circumstances, with an insulation value of up to 1.0E+9 ohms. A variety of factors can cause the insulation of MLCC to drop and cause leakage.
(1) Surface insulation decline caused by surface dirt, this kind of leakage current is not very large, generally microampere level. The insulation value will increase when hot air blows.
(2) Internal cracks, there are cracks caused by welding and MLCC manufacturing is not good. The leakage current caused by this kind of cracks will continue to rise, and in severe cases will cause local explosions and fires.