Power module performance requirements for electrolytic capacitors

The electrolytic capacitor is one of the tense components in the primary and secondary loop filter circuits in the module power supply. Its equivalent circuit can be considered as the series connection of an ideal capacitor, parasitic inductance and equivalent series resistance. Most of the electrolytic capacitors adopt the winding structure, which is easy to expand the volume. The capacitance per unit volume is very large, several to several tens of times larger than other capacitors. The capacitance is proportional to the volume, and the switching power supply is becoming more and more highly obedient and modular. It is necessary to explore new methods to obtain large capacitance and small volume capacitors.
Once the active filter circuit is used on the primary side of the switching power supply, the use environment of aluminum electrolytic capacitors will become more severe. For example, the high-frequency pulse current is mainly a pulsating current of 20 kHz to 100 kHz, and it will increase greatly. The main switch tube of the power converter heats up, which will cause the surrounding temperature of the aluminum electrolytic capacitor to rise.

Most power converters use boost circuits and require high-voltage aluminum electrolytic capacitors. If you use the past technology to manufacture aluminum electrolytic capacitors, you have to choose a large-size capacitor because you want to draw a larger pulsating current than before. As a result, the volume of the power supply increases, making it difficult to use in small electronic devices. Therefore, in order to meet the needs of module power supply, new electrolytic capacitors must be developed, which require small size, large capacity, high voltage resistance, high frequency and low impedance, and ripple current resistance. And working in a high temperature environment requires a long life.

The life of an electrolytic capacitor is also related to the ratio of the AC current of the capacitor working for a long time to the rated pulse current. Normally refers to the measured value at an ambient temperature of 85°C, or the data measured at 125°C for a high-temperature electrolytic capacitor. The larger the ratio, the shorter the life of the electrolytic capacitor. When the current flowing through the electrolytic capacitor is 3.8 times the rated current, the electrolytic capacitor is usually damaged. For ordinary applications, when the ratio of AC current to rated pulse current is less than 3.0 times, the life expectancy is satisfied.
As usual, the electrolytic capacitor in the ACDC module power supply is an indispensable key component, but problems such as large internal loss, large electrostatic capacitance deviation, large leakage current, and poor high and low temperature characteristics of the electrolytic capacitor will lead to poor reliability and short life. The ACDC module power supply without electrolytic capacitor is usually replaced by ceramic capacitors, thereby enhancing the reliability of the power supply and extending the service life.